€•®     Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ)/translations/zh_CN/filesystems/fuse/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ)/translations/zh_TW/filesystems/fuse/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ)/translations/it_IT/filesystems/fuse/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ)/translations/ja_JP/filesystems/fuse/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ)/translations/ko_KR/filesystems/fuse/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒPortuguese (Brazilian)”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ)/translations/pt_BR/filesystems/fuse/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh–sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ)/translations/sp_SP/filesystems/fuse/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒcomment”“”)”}”(hŒ SPDX-License-Identifier: GPL-2.0”h]”hŒ SPDX-License-Identifier: GPL-2.0”…””}”hh·sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1hµhhh²hh³ŒC/var/lib/git/docbuild/linux/Documentation/filesystems/fuse/fuse.rst”h´KubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒFUSE Overview”h]”hŒFUSE Overview”…””}”(hhÏh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhhÊh²hh³hÇh´KubhÉ)”}”(hhh]”(hÎ)”}”(hŒDefinitions”h]”hŒDefinitions”…””}”(hhàh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhhÝh²hh³hÇh´KubhŒdefinition_list”“”)”}”(hhh]”(hŒdefinition_list_item”“”)”}”(hŒ´Userspace filesystem:
A filesystem in which data and metadata are provided by an ordinary
userspace process.  The filesystem can be accessed normally through
the kernel interface.
”h]”(hŒterm”“”)”}”(hŒUserspace filesystem:”h]”hŒUserspace filesystem:”…””}”(hhûh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´KhhõubhŒ
definition”“”)”}”(hhh]”hŒ	paragraph”“”)”}”(hŒA filesystem in which data and metadata are provided by an ordinary
userspace process.  The filesystem can be accessed normally through
the kernel interface.”h]”hŒA filesystem in which data and metadata are provided by an ordinary
userspace process.  The filesystem can be accessed normally through
the kernel interface.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Khj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hhõubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´Khhðubhô)”}”(hŒVFilesystem daemon:
The process(es) providing the data and metadata of the filesystem.
”h]”(hú)”}”(hŒFilesystem daemon:”h]”hŒFilesystem daemon:”…””}”(hj.  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´Khj*  ubj
  )”}”(hhh]”j  )”}”(hŒBThe process(es) providing the data and metadata of the filesystem.”h]”hŒBThe process(es) providing the data and metadata of the filesystem.”…””}”(hj?  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Khj<  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj*  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´Khhðh²hubhô)”}”(hX&  Non-privileged mount (or user mount):
A userspace filesystem mounted by a non-privileged (non-root) user.
The filesystem daemon is running with the privileges of the mounting
user.  NOTE: this is not the same as mounts allowed with the "user"
option in /etc/fstab, which is not discussed here.
”h]”(hú)”}”(hŒ%Non-privileged mount (or user mount):”h]”hŒ%Non-privileged mount (or user mount):”…””}”(hj]  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´KhjY  ubj
  )”}”(hhh]”j  )”}”(hŒÿA userspace filesystem mounted by a non-privileged (non-root) user.
The filesystem daemon is running with the privileges of the mounting
user.  NOTE: this is not the same as mounts allowed with the "user"
option in /etc/fstab, which is not discussed here.”h]”hX  A userspace filesystem mounted by a non-privileged (non-root) user.
The filesystem daemon is running with the privileges of the mounting
user.  NOTE: this is not the same as mounts allowed with the â€œuserâ€
option in /etc/fstab, which is not discussed here.”…””}”(hjn  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Khjk  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjY  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´Khhðh²hubhô)”}”(hXR  Filesystem connection:
A connection between the filesystem daemon and the kernel.  The
connection exists until either the daemon dies, or the filesystem is
umounted.  Note that detaching (or lazy umounting) the filesystem
does *not* break the connection, in this case it will exist until
the last reference to the filesystem is released.
”h]”(hú)”}”(hŒFilesystem connection:”h]”hŒFilesystem connection:”…””}”(hjŒ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´Khjˆ  ubj
  )”}”(hhh]”j  )”}”(hX:  A connection between the filesystem daemon and the kernel.  The
connection exists until either the daemon dies, or the filesystem is
umounted.  Note that detaching (or lazy umounting) the filesystem
does *not* break the connection, in this case it will exist until
the last reference to the filesystem is released.”h]”(hŒÌA connection between the filesystem daemon and the kernel.  The
connection exists until either the daemon dies, or the filesystem is
umounted.  Note that detaching (or lazy umounting) the filesystem
does ”…””}”(hj  h²hh³Nh´NubhŒemphasis”“”)”}”(hŒ*not*”h]”hŒnot”…””}”(hj§  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¥  hj  ubhŒi break the connection, in this case it will exist until
the last reference to the filesystem is released.”…””}”(hj  h²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Khjš  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjˆ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´Khhðh²hubhô)”}”(hŒ-Mount owner:
The user who does the mounting.
”h]”(hú)”}”(hŒMount owner:”h]”hŒMount owner:”…””}”(hjÏ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´K hjË  ubj
  )”}”(hhh]”j  )”}”(hŒThe user who does the mounting.”h]”hŒThe user who does the mounting.”…””}”(hjà  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K hjÝ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjË  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´K hhðh²hubhô)”}”(hŒ8User:
The user who is performing filesystem operations.
”h]”(hú)”}”(hŒUser:”h]”hŒUser:”…””}”(hjþ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´K#hjú  ubj
  )”}”(hhh]”j  )”}”(hŒ1The user who is performing filesystem operations.”h]”hŒ1The user who is performing filesystem operations.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K#hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjú  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´K#hhðh²hubeh}”(h]”h ]”h"]”h$]”h&]”uh1hîhhÝh²hh³hÇh´Nubeh}”(h]”Œdefinitions”ah ]”h"]”Œdefinitions”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´KubhÉ)”}”(hhh]”(hÎ)”}”(hŒWhat is FUSE?”h]”hŒWhat is FUSE?”…””}”(hj:  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhj7  h²hh³hÇh´K&ubj  )”}”(hŒ–FUSE is a userspace filesystem framework.  It consists of a kernel
module (fuse.ko), a userspace library (libfuse.*) and a mount utility
(fusermount).”h]”hŒ–FUSE is a userspace filesystem framework.  It consists of a kernel
module (fuse.ko), a userspace library (libfuse.*) and a mount utility
(fusermount).”…””}”(hjH  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K(hj7  h²hubj  )”}”(hŒáOne of the most important features of FUSE is allowing secure,
non-privileged mounts.  This opens up new possibilities for the use of
filesystems.  A good example is sshfs: a secure network filesystem
using the sftp protocol.”h]”hŒáOne of the most important features of FUSE is allowing secure,
non-privileged mounts.  This opens up new possibilities for the use of
filesystems.  A good example is sshfs: a secure network filesystem
using the sftp protocol.”…””}”(hjV  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K,hj7  h²hubj  )”}”(hŒjThe userspace library and utilities are available from the
`FUSE homepage: <https://github.com/libfuse/>`_”h]”(hŒ;The userspace library and utilities are available from the
”…””}”(hjd  h²hh³Nh´NubhŒ	reference”“”)”}”(hŒ/`FUSE homepage: <https://github.com/libfuse/>`_”h]”hŒFUSE homepage:”…””}”(hjn  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”Œname”ŒFUSE homepage:”Œrefuri”Œhttps://github.com/libfuse/”uh1jl  hjd  ubhŒtarget”“”)”}”(hŒ <https://github.com/libfuse/>”h]”h}”(h]”Œfuse-homepage”ah ]”h"]”Œfuse homepage:”ah$]”h&]”Œrefuri”j  uh1j€  Œ
referenced”Khjd  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K1hj7  h²hubeh}”(h]”Œwhat-is-fuse”ah ]”h"]”Œwhat is fuse?”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´K&ubhÉ)”}”(hhh]”(hÎ)”}”(hŒFilesystem type”h]”hŒFilesystem type”…””}”(hj¡  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhjž  h²hh³hÇh´K5ubj  )”}”(hŒBThe filesystem type given to mount(2) can be one of the following:”h]”hŒBThe filesystem type given to mount(2) can be one of the following:”…””}”(hj¯  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K7hjž  h²hubhŒblock_quote”“”)”}”(hX=  fuse
  This is the usual way to mount a FUSE filesystem.  The first
  argument of the mount system call may contain an arbitrary string,
  which is not interpreted by the kernel.

fuseblk
  The filesystem is block device based.  The first argument of the
  mount system call is interpreted as the name of the device.
”h]”hï)”}”(hhh]”(hô)”}”(hŒ­fuse
This is the usual way to mount a FUSE filesystem.  The first
argument of the mount system call may contain an arbitrary string,
which is not interpreted by the kernel.
”h]”(hú)”}”(hŒfuse”h]”hŒfuse”…””}”(hjÊ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´K<hjÆ  ubj
  )”}”(hhh]”j  )”}”(hŒ§This is the usual way to mount a FUSE filesystem.  The first
argument of the mount system call may contain an arbitrary string,
which is not interpreted by the kernel.”h]”hŒ§This is the usual way to mount a FUSE filesystem.  The first
argument of the mount system call may contain an arbitrary string,
which is not interpreted by the kernel.”…””}”(hjÛ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K:hjØ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjÆ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´K<hjÃ  ubhô)”}”(hŒ…fuseblk
The filesystem is block device based.  The first argument of the
mount system call is interpreted as the name of the device.
”h]”(hú)”}”(hŒfuseblk”h]”hŒfuseblk”…””}”(hjù  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´K@hjõ  ubj
  )”}”(hhh]”j  )”}”(hŒ|The filesystem is block device based.  The first argument of the
mount system call is interpreted as the name of the device.”h]”hŒ|The filesystem is block device based.  The first argument of the
mount system call is interpreted as the name of the device.”…””}”(hj
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K?hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjõ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´K@hjÃ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hîhj¿  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´K9hjž  h²hubeh}”(h]”Œfilesystem-type”ah ]”h"]”Œfilesystem type”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´K5ubhÉ)”}”(hhh]”(hÎ)”}”(hŒMount options”h]”hŒMount options”…””}”(hj;  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhj8  h²hh³hÇh´KCubhï)”}”(hhh]”(hô)”}”(hŒºfd=N
The file descriptor to use for communication between the userspace
filesystem and the kernel.  The file descriptor must have been
obtained by opening the FUSE device ('/dev/fuse').
”h]”(hú)”}”(hŒfd=N”h]”hŒfd=N”…””}”(hjP  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´KHhjL  ubj
  )”}”(hhh]”j  )”}”(hŒ´The file descriptor to use for communication between the userspace
filesystem and the kernel.  The file descriptor must have been
obtained by opening the FUSE device ('/dev/fuse').”h]”hŒ¸The file descriptor to use for communication between the userspace
filesystem and the kernel.  The file descriptor must have been
obtained by opening the FUSE device (â€˜/dev/fuseâ€™).”…””}”(hja  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KFhj^  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjL  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´KHhjI  ubhô)”}”(hŒKrootmode=M
The file mode of the filesystem's root in octal representation.
”h]”(hú)”}”(hŒ
rootmode=M”h]”hŒ
rootmode=M”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´KKhj{  ubj
  )”}”(hhh]”j  )”}”(hŒ?The file mode of the filesystem's root in octal representation.”h]”hŒAThe file mode of the filesystemâ€™s root in octal representation.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KKhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj{  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´KKhjI  h²hubhô)”}”(hŒ2user_id=N
The numeric user id of the mount owner.
”h]”(hú)”}”(hŒ	user_id=N”h]”hŒ	user_id=N”…””}”(hj®  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´KNhjª  ubj
  )”}”(hhh]”j  )”}”(hŒ'The numeric user id of the mount owner.”h]”hŒ'The numeric user id of the mount owner.”…””}”(hj¿  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KNhj¼  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjª  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´KNhjI  h²hubhô)”}”(hŒ4group_id=N
The numeric group id of the mount owner.
”h]”(hú)”}”(hŒ
group_id=N”h]”hŒ
group_id=N”…””}”(hjÝ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´KQhjÙ  ubj
  )”}”(hhh]”j  )”}”(hŒ(The numeric group id of the mount owner.”h]”hŒ(The numeric group id of the mount owner.”…””}”(hjî  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KQhjë  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjÙ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´KQhjI  h²hubhô)”}”(hXq  default_permissions
By default FUSE doesn't check file access permissions, the
filesystem is free to implement its access policy or leave it to
the underlying file access mechanism (e.g. in case of network
filesystems).  This option enables permission checking, restricting
access based on file mode.  It is usually useful together with the
'allow_other' mount option.
”h]”(hú)”}”(hŒdefault_permissions”h]”hŒdefault_permissions”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´KYhj  ubj
  )”}”(hhh]”j  )”}”(hX\  By default FUSE doesn't check file access permissions, the
filesystem is free to implement its access policy or leave it to
the underlying file access mechanism (e.g. in case of network
filesystems).  This option enables permission checking, restricting
access based on file mode.  It is usually useful together with the
'allow_other' mount option.”h]”hXb  By default FUSE doesnâ€™t check file access permissions, the
filesystem is free to implement its access policy or leave it to
the underlying file access mechanism (e.g. in case of network
filesystems).  This option enables permission checking, restricting
access based on file mode.  It is usually useful together with the
â€˜allow_otherâ€™ mount option.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KThj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´KYhjI  h²hubhô)”}”(hŒòallow_other
This option overrides the security measure restricting file access
to the user mounting the filesystem.  This option is by default only
allowed to root, but this restriction can be removed with a
(userspace) configuration option.
”h]”(hú)”}”(hŒallow_other”h]”hŒallow_other”…””}”(hj;  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´K_hj7  ubj
  )”}”(hhh]”j  )”}”(hŒåThis option overrides the security measure restricting file access
to the user mounting the filesystem.  This option is by default only
allowed to root, but this restriction can be removed with a
(userspace) configuration option.”h]”hŒåThis option overrides the security measure restricting file access
to the user mounting the filesystem.  This option is by default only
allowed to root, but this restriction can be removed with a
(userspace) configuration option.”…””}”(hjL  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K\hjI  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj7  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´K_hjI  h²hubhô)”}”(hŒÅmax_read=N
With this option the maximum size of read operations can be set.
The default is infinite.  Note that the size of read requests is
limited anyway to 32 pages (which is 128kbyte on i386).
”h]”(hú)”}”(hŒ
max_read=N”h]”hŒ
max_read=N”…””}”(hjj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´Kdhjf  ubj
  )”}”(hhh]”j  )”}”(hŒ¹With this option the maximum size of read operations can be set.
The default is infinite.  Note that the size of read requests is
limited anyway to 32 pages (which is 128kbyte on i386).”h]”hŒ¹With this option the maximum size of read operations can be set.
The default is infinite.  Note that the size of read requests is
limited anyway to 32 pages (which is 128kbyte on i386).”…””}”(hj{  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kbhjx  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hjf  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´KdhjI  h²hubhô)”}”(hŒ|blksize=N
Set the block size for the filesystem.  The default is 512.  This
option is only valid for 'fuseblk' type mounts.
”h]”(hú)”}”(hŒ	blksize=N”h]”hŒ	blksize=N”…””}”(hj™  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´Khhj•  ubj
  )”}”(hhh]”j  )”}”(hŒqSet the block size for the filesystem.  The default is 512.  This
option is only valid for 'fuseblk' type mounts.”h]”hŒuSet the block size for the filesystem.  The default is 512.  This
option is only valid for â€˜fuseblkâ€™ type mounts.”…””}”(hjª  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kghj§  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj•  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´KhhjI  h²hubeh}”(h]”h ]”h"]”h$]”h&]”uh1hîhj8  h²hh³hÇh´Nubeh}”(h]”Œmount-options”ah ]”h"]”Œmount options”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´KCubhÉ)”}”(hhh]”(hÎ)”}”(hŒControl filesystem”h]”hŒControl filesystem”…””}”(hjÕ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhjÒ  h²hh³hÇh´Kkubj  )”}”(hŒ@There's a control filesystem for FUSE, which can be mounted by::”h]”hŒAThereâ€™s a control filesystem for FUSE, which can be mounted by:”…””}”(hjã  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KmhjÒ  h²hubhŒliteral_block”“”)”}”(hŒ.mount -t fusectl none /sys/fs/fuse/connections”h]”hŒ.mount -t fusectl none /sys/fs/fuse/connections”…””}”hjó  sbah}”(h]”h ]”h"]”h$]”h&]”hÅhÆuh1jñ  h³hÇh´KohjÒ  h²hubj  )”}”(hŒoMounting it under the '/sys/fs/fuse/connections' directory makes it
backwards compatible with earlier versions.”h]”hŒsMounting it under the â€˜/sys/fs/fuse/connectionsâ€™ directory makes it
backwards compatible with earlier versions.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KqhjÒ  h²hubj  )”}”(hŒ[Under the fuse control filesystem each connection has a directory
named by a unique number.”h]”hŒ[Under the fuse control filesystem each connection has a directory
named by a unique number.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KthjÒ  h²hubj  )”}”(hŒDFor each connection the following files exist within this directory:”h]”hŒDFor each connection the following files exist within this directory:”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KwhjÒ  h²hubj¾  )”}”(hXg  waiting
  The number of requests which are waiting to be transferred to
  userspace or being processed by the filesystem daemon.  If there is
  no filesystem activity and 'waiting' is non-zero, then the
  filesystem is hung or deadlocked.

abort
  Writing anything into this file will abort the filesystem
  connection.  This means that all waiting requests will be aborted an
  error returned for all aborted and new requests.

max_background
  The maximum number of background requests that can be outstanding
  at a time. When the number of background requests reaches this limit,
  further requests will be blocked until some are completed, potentially
  causing I/O operations to stall.

congestion_threshold
  The threshold of background requests at which the kernel considers
  the filesystem to be congested. When the number of background requests
  exceeds this value, the kernel will skip asynchronous readahead
  operations, reducing read-ahead optimizations but preserving essential
  I/O, as well as suspending non-synchronous writeback operations
  (WB_SYNC_NONE), delaying page cache flushing to the filesystem.
”h]”hï)”}”(hhh]”(hô)”}”(hŒçwaiting
The number of requests which are waiting to be transferred to
userspace or being processed by the filesystem daemon.  If there is
no filesystem activity and 'waiting' is non-zero, then the
filesystem is hung or deadlocked.
”h]”(hú)”}”(hŒwaiting”h]”hŒwaiting”…””}”(hj6  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´K}hj2  ubj
  )”}”(hhh]”j  )”}”(hŒÞThe number of requests which are waiting to be transferred to
userspace or being processed by the filesystem daemon.  If there is
no filesystem activity and 'waiting' is non-zero, then the
filesystem is hung or deadlocked.”h]”hŒâThe number of requests which are waiting to be transferred to
userspace or being processed by the filesystem daemon.  If there is
no filesystem activity and â€˜waitingâ€™ is non-zero, then the
filesystem is hung or deadlocked.”…””}”(hjG  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KzhjD  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj2  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´K}hj/  ubhô)”}”(hŒ¶abort
Writing anything into this file will abort the filesystem
connection.  This means that all waiting requests will be aborted an
error returned for all aborted and new requests.
”h]”(hú)”}”(hŒabort”h]”hŒabort”…””}”(hje  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´K‚hja  ubj
  )”}”(hhh]”j  )”}”(hŒ¯Writing anything into this file will abort the filesystem
connection.  This means that all waiting requests will be aborted an
error returned for all aborted and new requests.”h]”hŒ¯Writing anything into this file will abort the filesystem
connection.  This means that all waiting requests will be aborted an
error returned for all aborted and new requests.”…””}”(hjv  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K€hjs  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hja  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´K‚hj/  ubhô)”}”(hŒÿmax_background
The maximum number of background requests that can be outstanding
at a time. When the number of background requests reaches this limit,
further requests will be blocked until some are completed, potentially
causing I/O operations to stall.
”h]”(hú)”}”(hŒmax_background”h]”hŒmax_background”…””}”(hj”  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´Kˆhj  ubj
  )”}”(hhh]”j  )”}”(hŒïThe maximum number of background requests that can be outstanding
at a time. When the number of background requests reaches this limit,
further requests will be blocked until some are completed, potentially
causing I/O operations to stall.”h]”hŒïThe maximum number of background requests that can be outstanding
at a time. When the number of background requests reaches this limit,
further requests will be blocked until some are completed, potentially
causing I/O operations to stall.”…””}”(hj¥  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K…hj¢  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´Kˆhj/  ubhô)”}”(hX¦  congestion_threshold
The threshold of background requests at which the kernel considers
the filesystem to be congested. When the number of background requests
exceeds this value, the kernel will skip asynchronous readahead
operations, reducing read-ahead optimizations but preserving essential
I/O, as well as suspending non-synchronous writeback operations
(WB_SYNC_NONE), delaying page cache flushing to the filesystem.
”h]”(hú)”}”(hŒcongestion_threshold”h]”hŒcongestion_threshold”…””}”(hjÃ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hùh³hÇh´Khj¿  ubj
  )”}”(hhh]”j  )”}”(hX  The threshold of background requests at which the kernel considers
the filesystem to be congested. When the number of background requests
exceeds this value, the kernel will skip asynchronous readahead
operations, reducing read-ahead optimizations but preserving essential
I/O, as well as suspending non-synchronous writeback operations
(WB_SYNC_NONE), delaying page cache flushing to the filesystem.”h]”hX  The threshold of background requests at which the kernel considers
the filesystem to be congested. When the number of background requests
exceeds this value, the kernel will skip asynchronous readahead
operations, reducing read-ahead optimizations but preserving essential
I/O, as well as suspending non-synchronous writeback operations
(WB_SYNC_NONE), delaying page cache flushing to the filesystem.”…””}”(hjÔ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K‹hjÑ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j	  hj¿  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hóh³hÇh´Khj/  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hîhj+  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´KyhjÒ  h²hubj  )”}”(hŒ:Only the owner of the mount may read or write these files.”h]”hŒ:Only the owner of the mount may read or write these files.”…””}”(hjú  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K’hjÒ  h²hubhÉ)”}”(hhh]”(hÎ)”}”(hŒ"Interrupting filesystem operations”h]”hŒ"Interrupting filesystem operations”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhj  h²hh³hÇh´K•ubj  )”}”(hŒYIf a process issuing a FUSE filesystem request is interrupted, the
following will happen:”h]”hŒYIf a process issuing a FUSE filesystem request is interrupted, the
following will happen:”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K—hj  h²hubj¾  )”}”(hXÿ  -  If the request is not yet sent to userspace AND the signal is
   fatal (SIGKILL or unhandled fatal signal), then the request is
   dequeued and returns immediately.

-  If the request is not yet sent to userspace AND the signal is not
   fatal, then an interrupted flag is set for the request.  When
   the request has been successfully transferred to userspace and
   this flag is set, an INTERRUPT request is queued.

-  If the request is already sent to userspace, then an INTERRUPT
   request is queued.
”h]”hŒbullet_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒŸIf the request is not yet sent to userspace AND the signal is
fatal (SIGKILL or unhandled fatal signal), then the request is
dequeued and returns immediately.
”h]”j  )”}”(hŒžIf the request is not yet sent to userspace AND the signal is
fatal (SIGKILL or unhandled fatal signal), then the request is
dequeued and returns immediately.”h]”hŒžIf the request is not yet sent to userspace AND the signal is
fatal (SIGKILL or unhandled fatal signal), then the request is
dequeued and returns immediately.”…””}”(hj6  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kšhj2  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj-  ubj1  )”}”(hŒñIf the request is not yet sent to userspace AND the signal is not
fatal, then an interrupted flag is set for the request.  When
the request has been successfully transferred to userspace and
this flag is set, an INTERRUPT request is queued.
”h]”j  )”}”(hŒðIf the request is not yet sent to userspace AND the signal is not
fatal, then an interrupted flag is set for the request.  When
the request has been successfully transferred to userspace and
this flag is set, an INTERRUPT request is queued.”h]”hŒðIf the request is not yet sent to userspace AND the signal is not
fatal, then an interrupted flag is set for the request.  When
the request has been successfully transferred to userspace and
this flag is set, an INTERRUPT request is queued.”…””}”(hjN  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KžhjJ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj-  ubj1  )”}”(hŒRIf the request is already sent to userspace, then an INTERRUPT
request is queued.
”h]”j  )”}”(hŒQIf the request is already sent to userspace, then an INTERRUPT
request is queued.”h]”hŒQIf the request is already sent to userspace, then an INTERRUPT
request is queued.”…””}”(hjf  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K£hjb  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj-  ubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1j+  h³hÇh´Kšhj'  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´Kšhj  h²hubj  )”}”(hŒ…INTERRUPT requests take precedence over other requests, so the
userspace filesystem will receive queued INTERRUPTs before any others.”h]”hŒ…INTERRUPT requests take precedence over other requests, so the
userspace filesystem will receive queued INTERRUPTs before any others.”…””}”(hjˆ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K¦hj  h²hubj  )”}”(hŒ¡The userspace filesystem may ignore the INTERRUPT requests entirely,
or may honor them by sending a reply to the *original* request, with
the error set to EINTR.”h]”(hŒqThe userspace filesystem may ignore the INTERRUPT requests entirely,
or may honor them by sending a reply to the ”…””}”(hj–  h²hh³Nh´Nubj¦  )”}”(hŒ
*original*”h]”hŒoriginal”…””}”(hjž  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¥  hj–  ubhŒ& request, with
the error set to EINTR.”…””}”(hj–  h²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K©hj  h²hubj  )”}”(hŒˆIt is also possible that there's a race between processing the
original request and its INTERRUPT request.  There are two possibilities:”h]”hŒŠIt is also possible that thereâ€™s a race between processing the
original request and its INTERRUPT request.  There are two possibilities:”…””}”(hj¶  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K­hj  h²hubj¾  )”}”(hŒ©1. The INTERRUPT request is processed before the original request is
   processed

2. The INTERRUPT request is processed after the original request has
   been answered
”h]”hŒenumerated_list”“”)”}”(hhh]”(j1  )”}”(hŒLThe INTERRUPT request is processed before the original request is
processed
”h]”j  )”}”(hŒKThe INTERRUPT request is processed before the original request is
processed”h]”hŒKThe INTERRUPT request is processed before the original request is
processed”…””}”(hjÑ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K°hjÍ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjÊ  ubj1  )”}”(hŒPThe INTERRUPT request is processed after the original request has
been answered
”h]”j  )”}”(hŒOThe INTERRUPT request is processed after the original request has
been answered”h]”hŒOThe INTERRUPT request is processed after the original request has
been answered”…””}”(hjé  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K³hjå  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjÊ  ubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ.”uh1jÈ  hjÄ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´K°hj  h²hubj  )”}”(hX.  If the filesystem cannot find the original request, it should wait for
some timeout and/or a number of new requests to arrive, after which it
should reply to the INTERRUPT request with an EAGAIN error.  In case
1) the INTERRUPT request will be requeued.  In case 2) the INTERRUPT
reply will be ignored.”h]”hX.  If the filesystem cannot find the original request, it should wait for
some timeout and/or a number of new requests to arrive, after which it
should reply to the INTERRUPT request with an EAGAIN error.  In case
1) the INTERRUPT request will be requeued.  In case 2) the INTERRUPT
reply will be ignored.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K¶hj  h²hubeh}”(h]”Œ"interrupting-filesystem-operations”ah ]”h"]”Œ"interrupting filesystem operations”ah$]”h&]”uh1hÈhjÒ  h²hh³hÇh´K•ubeh}”(h]”Œcontrol-filesystem”ah ]”h"]”Œcontrol filesystem”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´KkubhÉ)”}”(hhh]”(hÎ)”}”(hŒ Aborting a filesystem connection”h]”hŒ Aborting a filesystem connection”…””}”(hj/  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhj,  h²hh³hÇh´K½ubj  )”}”(hŒoIt is possible to get into certain situations where the filesystem is
not responding.  Reasons for this may be:”h]”hŒoIt is possible to get into certain situations where the filesystem is
not responding.  Reasons for this may be:”…””}”(hj=  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K¿hj,  h²hubj¾  )”}”(hŒya) Broken userspace filesystem implementation

b) Network connection down

c) Accidental deadlock

d) Malicious deadlock
”h]”jÉ  )”}”(hhh]”(j1  )”}”(hŒ+Broken userspace filesystem implementation
”h]”j  )”}”(hŒ*Broken userspace filesystem implementation”h]”hŒ*Broken userspace filesystem implementation”…””}”(hjV  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÂhjR  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjO  ubj1  )”}”(hŒNetwork connection down
”h]”j  )”}”(hŒNetwork connection down”h]”hŒNetwork connection down”…””}”(hjn  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÄhjj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjO  ubj1  )”}”(hŒAccidental deadlock
”h]”j  )”}”(hŒAccidental deadlock”h]”hŒAccidental deadlock”…””}”(hj†  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÆhj‚  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjO  ubj1  )”}”(hŒMalicious deadlock
”h]”j  )”}”(hŒMalicious deadlock”h]”hŒMalicious deadlock”…””}”(hjž  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÈhjš  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjO  ubeh}”(h]”h ]”h"]”h$]”h&]”j  Œ
loweralpha”j  hj  Œ)”uh1jÈ  hjK  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´KÂhj,  h²hubj  )”}”(hŒ*(For more on c) and d) see later sections)”h]”hŒ*(For more on c) and d) see later sections)”…””}”(hjÀ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÊhj,  h²hubj  )”}”(hŒxIn either of these cases it may be useful to abort the connection to
the filesystem.  There are several ways to do this:”h]”hŒxIn either of these cases it may be useful to abort the connection to
the filesystem.  There are several ways to do this:”…””}”(hjÎ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÌhj,  h²hubj¾  )”}”(hX  - Kill the filesystem daemon.  Works in case of a) and b)

- Kill the filesystem daemon and all users of the filesystem.  Works
  in all cases except some malicious deadlocks

- Use forced umount (umount -f).  Works in all cases but only if
  filesystem is still attached (it hasn't been lazy unmounted)

- Abort filesystem through the FUSE control filesystem.  Most
  powerful method, always works.
”h]”j,  )”}”(hhh]”(j1  )”}”(hŒ8Kill the filesystem daemon.  Works in case of a) and b)
”h]”j  )”}”(hŒ7Kill the filesystem daemon.  Works in case of a) and b)”h]”hŒ7Kill the filesystem daemon.  Works in case of a) and b)”…””}”(hjç  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÏhjã  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjà  ubj1  )”}”(hŒpKill the filesystem daemon and all users of the filesystem.  Works
in all cases except some malicious deadlocks
”h]”j  )”}”(hŒoKill the filesystem daemon and all users of the filesystem.  Works
in all cases except some malicious deadlocks”h]”hŒoKill the filesystem daemon and all users of the filesystem.  Works
in all cases except some malicious deadlocks”…””}”(hjÿ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÑhjû  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjà  ubj1  )”}”(hŒ|Use forced umount (umount -f).  Works in all cases but only if
filesystem is still attached (it hasn't been lazy unmounted)
”h]”j  )”}”(hŒ{Use forced umount (umount -f).  Works in all cases but only if
filesystem is still attached (it hasn't been lazy unmounted)”h]”hŒ}Use forced umount (umount -f).  Works in all cases but only if
filesystem is still attached (it hasnâ€™t been lazy unmounted)”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÔhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjà  ubj1  )”}”(hŒ[Abort filesystem through the FUSE control filesystem.  Most
powerful method, always works.
”h]”j  )”}”(hŒZAbort filesystem through the FUSE control filesystem.  Most
powerful method, always works.”h]”hŒZAbort filesystem through the FUSE control filesystem.  Most
powerful method, always works.”…””}”(hj/  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´K×hj+  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjà  ubeh}”(h]”h ]”h"]”h$]”h&]”j€  j  uh1j+  h³hÇh´KÏhjÜ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´KÏhj,  h²hubeh}”(h]”Œ aborting-a-filesystem-connection”ah ]”h"]”Œ aborting a filesystem connection”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´K½ubhÉ)”}”(hhh]”(hÎ)”}”(hŒ"How do non-privileged mounts work?”h]”hŒ"How do non-privileged mounts work?”…””}”(hjZ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhjW  h²hh³hÇh´KÛubj  )”}”(hŒSince the mount() system call is a privileged operation, a helper
program (fusermount) is needed, which is installed setuid root.”h]”hŒSince the mount() system call is a privileged operation, a helper
program (fusermount) is needed, which is installed setuid root.”…””}”(hjh  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KÝhjW  h²hubj  )”}”(hŒ¹The implication of providing non-privileged mounts is that the mount
owner must not be able to use this capability to compromise the
system.  Obvious requirements arising from this are:”h]”hŒ¹The implication of providing non-privileged mounts is that the mount
owner must not be able to use this capability to compromise the
system.  Obvious requirements arising from this are:”…””}”(hjv  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´KàhjW  h²hubj¾  )”}”(hXO  A) mount owner should not be able to get elevated privileges with the
   help of the mounted filesystem

B) mount owner should not get illegitimate access to information from
   other users' and the super user's processes

C) mount owner should not be able to induce undesired behavior in
   other users' or the super user's processes
”h]”jÉ  )”}”(hhh]”(j1  )”}”(hŒbmount owner should not be able to get elevated privileges with the
help of the mounted filesystem
”h]”j  )”}”(hŒamount owner should not be able to get elevated privileges with the
help of the mounted filesystem”h]”hŒamount owner should not be able to get elevated privileges with the
help of the mounted filesystem”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kähj‹  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjˆ  ubj1  )”}”(hŒomount owner should not get illegitimate access to information from
other users' and the super user's processes
”h]”j  )”}”(hŒnmount owner should not get illegitimate access to information from
other users' and the super user's processes”h]”hŒrmount owner should not get illegitimate access to information from
other usersâ€™ and the super userâ€™s processes”…””}”(hj§  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kçhj£  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjˆ  ubj1  )”}”(hŒjmount owner should not be able to induce undesired behavior in
other users' or the super user's processes
”h]”j  )”}”(hŒimount owner should not be able to induce undesired behavior in
other users' or the super user's processes”h]”hŒmmount owner should not be able to induce undesired behavior in
other usersâ€™ or the super userâ€™s processes”…””}”(hj¿  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kêhj»  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjˆ  ubeh}”(h]”h ]”h"]”h$]”h&]”j  Œ
upperalpha”j  hj  j¹  uh1jÈ  hj„  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´KähjW  h²hubeh}”(h]”Œ!how-do-non-privileged-mounts-work”ah ]”h"]”Œ"how do non-privileged mounts work?”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´KÛubhÉ)”}”(hhh]”(hÎ)”}”(hŒHow are requirements fulfilled?”h]”hŒHow are requirements fulfilled?”…””}”(hjë  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhjè  h²hh³hÇh´Kîubj¾  )”}”(hX  A) The mount owner could gain elevated privileges by either:

   1. creating a filesystem containing a device file, then opening this device

   2. creating a filesystem containing a suid or sgid application, then executing this application

   The solution is not to allow opening device files and ignore
   setuid and setgid bits when executing programs.  To ensure this
   fusermount always adds "nosuid" and "nodev" to the mount options
   for non-privileged mounts.

B) If another user is accessing files or directories in the
   filesystem, the filesystem daemon serving requests can record the
   exact sequence and timing of operations performed.  This
   information is otherwise inaccessible to the mount owner, so this
   counts as an information leak.

   The solution to this problem will be presented in point 2) of C).

C) There are several ways in which the mount owner can induce
   undesired behavior in other users' processes, such as:

    1) mounting a filesystem over a file or directory which the mount
       owner could otherwise not be able to modify (or could only
       make limited modifications).

       This is solved in fusermount, by checking the access
       permissions on the mountpoint and only allowing the mount if
       the mount owner can do unlimited modification (has write
       access to the mountpoint, and mountpoint is not a "sticky"
       directory)

    2) Even if 1) is solved the mount owner can change the behavior
       of other users' processes.

        i) It can slow down or indefinitely delay the execution of a
           filesystem operation creating a DoS against the user or the
           whole system.  For example a suid application locking a
           system file, and then accessing a file on the mount owner's
           filesystem could be stopped, and thus causing the system
           file to be locked forever.

        ii) It can present files or directories of unlimited length, or
            directory structures of unlimited depth, possibly causing a
            system process to eat up diskspace, memory or other
            resources, again causing *DoS*.

       The solution to this as well as B) is not to allow processes
       to access the filesystem, which could otherwise not be
       monitored or manipulated by the mount owner.  Since if the
       mount owner can ptrace a process, it can do all of the above
       without using a FUSE mount, the same criteria as used in
       ptrace can be used to check if a process is allowed to access
       the filesystem or not.

       Note that the *ptrace* check is not strictly necessary to
       prevent C/2/i, it is enough to check if mount owner has enough
       privilege to send signal to the process accessing the
       filesystem, since *SIGSTOP* can be used to get a similar effect.
”h]”jÉ  )”}”(hhh]”(j1  )”}”(hXÂ  The mount owner could gain elevated privileges by either:

1. creating a filesystem containing a device file, then opening this device

2. creating a filesystem containing a suid or sgid application, then executing this application

The solution is not to allow opening device files and ignore
setuid and setgid bits when executing programs.  To ensure this
fusermount always adds "nosuid" and "nodev" to the mount options
for non-privileged mounts.
”h]”(j  )”}”(hŒ9The mount owner could gain elevated privileges by either:”h]”hŒ9The mount owner could gain elevated privileges by either:”…””}”(hj	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kðhj 	  ubjÉ  )”}”(hhh]”(j1  )”}”(hŒIcreating a filesystem containing a device file, then opening this device
”h]”j  )”}”(hŒHcreating a filesystem containing a device file, then opening this device”h]”hŒHcreating a filesystem containing a device file, then opening this device”…””}”(hj	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kòhj	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj	  ubj1  )”}”(hŒ]creating a filesystem containing a suid or sgid application, then executing this application
”h]”j  )”}”(hŒ\creating a filesystem containing a suid or sgid application, then executing this application”h]”hŒ\creating a filesystem containing a suid or sgid application, then executing this application”…””}”(hj1	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kôhj-	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj	  ubeh}”(h]”h ]”h"]”h$]”h&]”j  j  j  hj  j  uh1jÈ  hj 	  ubj  )”}”(hŒØThe solution is not to allow opening device files and ignore
setuid and setgid bits when executing programs.  To ensure this
fusermount always adds "nosuid" and "nodev" to the mount options
for non-privileged mounts.”h]”hŒàThe solution is not to allow opening device files and ignore
setuid and setgid bits when executing programs.  To ensure this
fusermount always adds â€œnosuidâ€ and â€œnodevâ€ to the mount options
for non-privileged mounts.”…””}”(hjK	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Köhj 	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjý  ubj1  )”}”(hXX  If another user is accessing files or directories in the
filesystem, the filesystem daemon serving requests can record the
exact sequence and timing of operations performed.  This
information is otherwise inaccessible to the mount owner, so this
counts as an information leak.

The solution to this problem will be presented in point 2) of C).
”h]”(j  )”}”(hX  If another user is accessing files or directories in the
filesystem, the filesystem daemon serving requests can record the
exact sequence and timing of operations performed.  This
information is otherwise inaccessible to the mount owner, so this
counts as an information leak.”h]”hX  If another user is accessing files or directories in the
filesystem, the filesystem daemon serving requests can record the
exact sequence and timing of operations performed.  This
information is otherwise inaccessible to the mount owner, so this
counts as an information leak.”…””}”(hjc	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Kûhj_	  ubj  )”}”(hŒAThe solution to this problem will be presented in point 2) of C).”h]”hŒAThe solution to this problem will be presented in point 2) of C).”…””}”(hjq	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mhj_	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjý  ubj1  )”}”(hXu  There are several ways in which the mount owner can induce
undesired behavior in other users' processes, such as:

 1) mounting a filesystem over a file or directory which the mount
    owner could otherwise not be able to modify (or could only
    make limited modifications).

    This is solved in fusermount, by checking the access
    permissions on the mountpoint and only allowing the mount if
    the mount owner can do unlimited modification (has write
    access to the mountpoint, and mountpoint is not a "sticky"
    directory)

 2) Even if 1) is solved the mount owner can change the behavior
    of other users' processes.

     i) It can slow down or indefinitely delay the execution of a
        filesystem operation creating a DoS against the user or the
        whole system.  For example a suid application locking a
        system file, and then accessing a file on the mount owner's
        filesystem could be stopped, and thus causing the system
        file to be locked forever.

     ii) It can present files or directories of unlimited length, or
         directory structures of unlimited depth, possibly causing a
         system process to eat up diskspace, memory or other
         resources, again causing *DoS*.

    The solution to this as well as B) is not to allow processes
    to access the filesystem, which could otherwise not be
    monitored or manipulated by the mount owner.  Since if the
    mount owner can ptrace a process, it can do all of the above
    without using a FUSE mount, the same criteria as used in
    ptrace can be used to check if a process is allowed to access
    the filesystem or not.

    Note that the *ptrace* check is not strictly necessary to
    prevent C/2/i, it is enough to check if mount owner has enough
    privilege to send signal to the process accessing the
    filesystem, since *SIGSTOP* can be used to get a similar effect.
”h]”(j  )”}”(hŒqThere are several ways in which the mount owner can induce
undesired behavior in other users' processes, such as:”h]”hŒsThere are several ways in which the mount owner can induce
undesired behavior in other usersâ€™ processes, such as:”…””}”(hj‰	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mhj…	  ubj¾  )”}”(hXã  1) mounting a filesystem over a file or directory which the mount
   owner could otherwise not be able to modify (or could only
   make limited modifications).

   This is solved in fusermount, by checking the access
   permissions on the mountpoint and only allowing the mount if
   the mount owner can do unlimited modification (has write
   access to the mountpoint, and mountpoint is not a "sticky"
   directory)

2) Even if 1) is solved the mount owner can change the behavior
   of other users' processes.

    i) It can slow down or indefinitely delay the execution of a
       filesystem operation creating a DoS against the user or the
       whole system.  For example a suid application locking a
       system file, and then accessing a file on the mount owner's
       filesystem could be stopped, and thus causing the system
       file to be locked forever.

    ii) It can present files or directories of unlimited length, or
        directory structures of unlimited depth, possibly causing a
        system process to eat up diskspace, memory or other
        resources, again causing *DoS*.

   The solution to this as well as B) is not to allow processes
   to access the filesystem, which could otherwise not be
   monitored or manipulated by the mount owner.  Since if the
   mount owner can ptrace a process, it can do all of the above
   without using a FUSE mount, the same criteria as used in
   ptrace can be used to check if a process is allowed to access
   the filesystem or not.

   Note that the *ptrace* check is not strictly necessary to
   prevent C/2/i, it is enough to check if mount owner has enough
   privilege to send signal to the process accessing the
   filesystem, since *SIGSTOP* can be used to get a similar effect.
”h]”jÉ  )”}”(hhh]”(j1  )”}”(hX‰  mounting a filesystem over a file or directory which the mount
owner could otherwise not be able to modify (or could only
make limited modifications).

This is solved in fusermount, by checking the access
permissions on the mountpoint and only allowing the mount if
the mount owner can do unlimited modification (has write
access to the mountpoint, and mountpoint is not a "sticky"
directory)
”h]”(j  )”}”(hŒ–mounting a filesystem over a file or directory which the mount
owner could otherwise not be able to modify (or could only
make limited modifications).”h]”hŒ–mounting a filesystem over a file or directory which the mount
owner could otherwise not be able to modify (or could only
make limited modifications).”…””}”(hj¢	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mhjž	  ubj  )”}”(hŒðThis is solved in fusermount, by checking the access
permissions on the mountpoint and only allowing the mount if
the mount owner can do unlimited modification (has write
access to the mountpoint, and mountpoint is not a "sticky"
directory)”h]”hŒôThis is solved in fusermount, by checking the access
permissions on the mountpoint and only allowing the mount if
the mount owner can do unlimited modification (has write
access to the mountpoint, and mountpoint is not a â€œstickyâ€
directory)”…””}”(hj°	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M
hjž	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj›	  ubj1  )”}”(hXü  Even if 1) is solved the mount owner can change the behavior
of other users' processes.

 i) It can slow down or indefinitely delay the execution of a
    filesystem operation creating a DoS against the user or the
    whole system.  For example a suid application locking a
    system file, and then accessing a file on the mount owner's
    filesystem could be stopped, and thus causing the system
    file to be locked forever.

 ii) It can present files or directories of unlimited length, or
     directory structures of unlimited depth, possibly causing a
     system process to eat up diskspace, memory or other
     resources, again causing *DoS*.

The solution to this as well as B) is not to allow processes
to access the filesystem, which could otherwise not be
monitored or manipulated by the mount owner.  Since if the
mount owner can ptrace a process, it can do all of the above
without using a FUSE mount, the same criteria as used in
ptrace can be used to check if a process is allowed to access
the filesystem or not.

Note that the *ptrace* check is not strictly necessary to
prevent C/2/i, it is enough to check if mount owner has enough
privilege to send signal to the process accessing the
filesystem, since *SIGSTOP* can be used to get a similar effect.
”h]”(j  )”}”(hŒWEven if 1) is solved the mount owner can change the behavior
of other users' processes.”h]”hŒYEven if 1) is solved the mount owner can change the behavior
of other usersâ€™ processes.”…””}”(hjÈ	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´MhjÄ	  ubj¾  )”}”(hX-  i) It can slow down or indefinitely delay the execution of a
   filesystem operation creating a DoS against the user or the
   whole system.  For example a suid application locking a
   system file, and then accessing a file on the mount owner's
   filesystem could be stopped, and thus causing the system
   file to be locked forever.

ii) It can present files or directories of unlimited length, or
    directory structures of unlimited depth, possibly causing a
    system process to eat up diskspace, memory or other
    resources, again causing *DoS*.
”h]”jÉ  )”}”(hhh]”(j1  )”}”(hX>  It can slow down or indefinitely delay the execution of a
filesystem operation creating a DoS against the user or the
whole system.  For example a suid application locking a
system file, and then accessing a file on the mount owner's
filesystem could be stopped, and thus causing the system
file to be locked forever.
”h]”j  )”}”(hX=  It can slow down or indefinitely delay the execution of a
filesystem operation creating a DoS against the user or the
whole system.  For example a suid application locking a
system file, and then accessing a file on the mount owner's
filesystem could be stopped, and thus causing the system
file to be locked forever.”h]”hX?  It can slow down or indefinitely delay the execution of a
filesystem operation creating a DoS against the user or the
whole system.  For example a suid application locking a
system file, and then accessing a file on the mount ownerâ€™s
filesystem could be stopped, and thus causing the system
file to be locked forever.”…””}”(hjá	  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´MhjÝ	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjÚ	  ubj1  )”}”(hŒÌIt can present files or directories of unlimited length, or
directory structures of unlimited depth, possibly causing a
system process to eat up diskspace, memory or other
resources, again causing *DoS*.
”h]”j  )”}”(hŒËIt can present files or directories of unlimited length, or
directory structures of unlimited depth, possibly causing a
system process to eat up diskspace, memory or other
resources, again causing *DoS*.”h]”(hŒÅIt can present files or directories of unlimited length, or
directory structures of unlimited depth, possibly causing a
system process to eat up diskspace, memory or other
resources, again causing ”…””}”(hjù	  h²hh³Nh´Nubj¦  )”}”(hŒ*DoS*”h]”hŒDoS”…””}”(hj
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¥  hjù	  ubhŒ.”…””}”(hjù	  h²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mhjõ	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjÚ	  ubeh}”(h]”h ]”h"]”h$]”h&]”j  Œ
lowerroman”j  hj  j¹  uh1jÈ  hjÖ	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´MhjÄ	  ubj  )”}”(hXy  The solution to this as well as B) is not to allow processes
to access the filesystem, which could otherwise not be
monitored or manipulated by the mount owner.  Since if the
mount owner can ptrace a process, it can do all of the above
without using a FUSE mount, the same criteria as used in
ptrace can be used to check if a process is allowed to access
the filesystem or not.”h]”hXy  The solution to this as well as B) is not to allow processes
to access the filesystem, which could otherwise not be
monitored or manipulated by the mount owner.  Since if the
mount owner can ptrace a process, it can do all of the above
without using a FUSE mount, the same criteria as used in
ptrace can be used to check if a process is allowed to access
the filesystem or not.”…””}”(hj,
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´MhjÄ	  ubj  )”}”(hŒïNote that the *ptrace* check is not strictly necessary to
prevent C/2/i, it is enough to check if mount owner has enough
privilege to send signal to the process accessing the
filesystem, since *SIGSTOP* can be used to get a similar effect.”h]”(hŒNote that the ”…””}”(hj:
  h²hh³Nh´Nubj¦  )”}”(hŒ*ptrace*”h]”hŒptrace”…””}”(hjB
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¥  hj:
  ubhŒ« check is not strictly necessary to
prevent C/2/i, it is enough to check if mount owner has enough
privilege to send signal to the process accessing the
filesystem, since ”…””}”(hj:
  h²hh³Nh´Nubj¦  )”}”(hŒ	*SIGSTOP*”h]”hŒSIGSTOP”…””}”(hjT
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¥  hj:
  ubhŒ% can be used to get a similar effect.”…””}”(hj:
  h²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M'hjÄ	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj›	  ubeh}”(h]”h ]”h"]”h$]”h&]”j  j  j  hj  j¹  uh1jÈ  hj—	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´Mhj…	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j0  hjý  ubeh}”(h]”h ]”h"]”h$]”h&]”j  jÙ  j  hj  j¹  uh1jÈ  hjù  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´Kðhjè  h²hubeh}”(h]”Œhow-are-requirements-fulfilled”ah ]”h"]”Œhow are requirements fulfilled?”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´KîubhÉ)”}”(hhh]”(hÎ)”}”(hŒ+I think these limitations are unacceptable?”h]”hŒ+I think these limitations are unacceptable?”…””}”(hj›
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhj˜
  h²hh³hÇh´M-ubj  )”}”(hŒ¼If a sysadmin trusts the users enough, or can ensure through other
measures, that system processes will never enter non-privileged
mounts, it can relax the last limitation in several ways:”h]”hŒ¼If a sysadmin trusts the users enough, or can ensure through other
measures, that system processes will never enter non-privileged
mounts, it can relax the last limitation in several ways:”…””}”(hj©
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M/hj˜
  h²hubj¾  )”}”(hXz  - With the 'user_allow_other' config option. If this config option is
  set, the mounting user can add the 'allow_other' mount option which
  disables the check for other users' processes.

  User namespaces have an unintuitive interaction with 'allow_other':
  an unprivileged user - normally restricted from mounting with
  'allow_other' - could do so in a user namespace where they're
  privileged. If any process could access such an 'allow_other' mount
  this would give the mounting user the ability to manipulate
  processes in user namespaces where they're unprivileged. For this
  reason 'allow_other' restricts access to users in the same userns
  or a descendant.

- With the 'allow_sys_admin_access' module option. If this option is
  set, super user's processes have unrestricted access to mounts
  irrespective of allow_other setting or user namespace of the
  mounting user.
”h]”j,  )”}”(hhh]”(j1  )”}”(hX  With the 'user_allow_other' config option. If this config option is
set, the mounting user can add the 'allow_other' mount option which
disables the check for other users' processes.

User namespaces have an unintuitive interaction with 'allow_other':
an unprivileged user - normally restricted from mounting with
'allow_other' - could do so in a user namespace where they're
privileged. If any process could access such an 'allow_other' mount
this would give the mounting user the ability to manipulate
processes in user namespaces where they're unprivileged. For this
reason 'allow_other' restricts access to users in the same userns
or a descendant.
”h]”(j  )”}”(hŒ¶With the 'user_allow_other' config option. If this config option is
set, the mounting user can add the 'allow_other' mount option which
disables the check for other users' processes.”h]”hŒÀWith the â€˜user_allow_otherâ€™ config option. If this config option is
set, the mounting user can add the â€˜allow_otherâ€™ mount option which
disables the check for other usersâ€™ processes.”…””}”(hjÂ
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M3hj¾
  ubj  )”}”(hXÔ  User namespaces have an unintuitive interaction with 'allow_other':
an unprivileged user - normally restricted from mounting with
'allow_other' - could do so in a user namespace where they're
privileged. If any process could access such an 'allow_other' mount
this would give the mounting user the ability to manipulate
processes in user namespaces where they're unprivileged. For this
reason 'allow_other' restricts access to users in the same userns
or a descendant.”h]”hXè  User namespaces have an unintuitive interaction with â€˜allow_otherâ€™:
an unprivileged user - normally restricted from mounting with
â€˜allow_otherâ€™ - could do so in a user namespace where theyâ€™re
privileged. If any process could access such an â€˜allow_otherâ€™ mount
this would give the mounting user the ability to manipulate
processes in user namespaces where theyâ€™re unprivileged. For this
reason â€˜allow_otherâ€™ restricts access to users in the same userns
or a descendant.”…””}”(hjÐ
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M7hj¾
  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj»
  ubj1  )”}”(hŒÎWith the 'allow_sys_admin_access' module option. If this option is
set, super user's processes have unrestricted access to mounts
irrespective of allow_other setting or user namespace of the
mounting user.
”h]”j  )”}”(hŒÍWith the 'allow_sys_admin_access' module option. If this option is
set, super user's processes have unrestricted access to mounts
irrespective of allow_other setting or user namespace of the
mounting user.”h]”hŒÓWith the â€˜allow_sys_admin_accessâ€™ module option. If this option is
set, super userâ€™s processes have unrestricted access to mounts
irrespective of allow_other setting or user namespace of the
mounting user.”…””}”(hjè
  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M@hjä
  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j0  hj»
  ubeh}”(h]”h ]”h"]”h$]”h&]”j€  j  uh1j+  h³hÇh´M3hj·
  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j½  h³hÇh´M3hj˜
  h²hubj  )”}”(hŒœNote that both of these relaxations expose the system to potential
information leak or *DoS* as described in points B and C/2/i-ii in the
preceding section.”h]”(hŒWNote that both of these relaxations expose the system to potential
information leak or ”…””}”(hj  h²hh³Nh´Nubj¦  )”}”(hŒ*DoS*”h]”hŒDoS”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¥  hj  ubhŒ@ as described in points B and C/2/i-ii in the
preceding section.”…””}”(hj  h²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´MEhj˜
  h²hubeh}”(h]”Œ*i-think-these-limitations-are-unacceptable”ah ]”h"]”Œ+i think these limitations are unacceptable?”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´M-ubhÉ)”}”(hhh]”(hÎ)”}”(hŒKernel - userspace interface”h]”hŒKernel - userspace interface”…””}”(hj3  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÍhj0  h²hh³hÇh´MJubj  )”}”(hŒhThe following diagram shows how a filesystem operation (in this
example unlink) is performed in FUSE. ::”h]”hŒeThe following diagram shows how a filesystem operation (in this
example unlink) is performed in FUSE.”…””}”(hjA  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´MLhj0  h²hubjò  )”}”(hXÞ  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
|                                    |
|                                    |  >sys_read()
|                                    |    >fuse_dev_read()
|                                    |      >request_wait()
|                                    |        [sleep on fc->waitq]
|                                    |
|  >sys_unlink()                     |
|    >fuse_unlink()                  |
|      [get request from             |
|       fc->unused_list]             |
|      >request_send()               |
|        [queue req on fc->pending]  |
|        [wake up fc->waitq]         |        [woken up]
|        >request_wait_answer()      |
|          [sleep on req->waitq]     |
|                                    |      <request_wait()
|                                    |      [remove req from fc->pending]
|                                    |      [copy req to read buffer]
|                                    |      [add req to fc->processing]
|                                    |    <fuse_dev_read()
|                                    |  <sys_read()
|                                    |
|                                    |  [perform unlink]
|                                    |
|                                    |  >sys_write()
|                                    |    >fuse_dev_write()
|                                    |      [look up req in fc->processing]
|                                    |      [remove from fc->processing]
|                                    |      [copy write buffer to req]
|          [woken up]                |      [wake up req->waitq]
|                                    |    <fuse_dev_write()
|                                    |  <sys_write()
|        <request_wait_answer()      |
|      <request_send()               |
|      [add request to               |
|       fc->unused_list]             |
|    <fuse_unlink()                  |
|  <sys_unlink()                     |”•“.      h]”hXÞ  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
|                                    |
|                                    |  >sys_read()
|                                    |    >fuse_dev_read()
|                                    |      >request_wait()
|                                    |        [sleep on fc->waitq]
|                                    |
|  >sys_unlink()                     |
|    >fuse_unlink()                  |
|      [get request from             |
|       fc->unused_list]             |
|      >request_send()               |
|        [queue req on fc->pending]  |
|        [wake up fc->waitq]         |        [woken up]
|        >request_wait_answer()      |
|          [sleep on req->waitq]     |
|                                    |      <request_wait()
|                                    |      [remove req from fc->pending]
|                                    |      [copy req to read buffer]
|                                    |      [add req to fc->processing]
|                                    |    <fuse_dev_read()
|                                    |  <sys_read()
|                                    |
|                                    |  [perform unlink]
|                                    |
|                                    |  >sys_write()
|                                    |    >fuse_dev_write()
|                                    |      [look up req in fc->processing]
|                                    |      [remove from fc->processing]
|                                    |      [copy write buffer to req]
|          [woken up]                |      [wake up req->waitq]
|                                    |    <fuse_dev_write()
|                                    |  <sys_write()
|        <request_wait_answer()      |
|      <request_send()               |
|      [add request to               |
|       fc->unused_list]             |
|    <fuse_unlink()                  |
|  <sys_unlink()                     |”…””}”hjO  sbah}”(h]”h ]”h"]”h$]”h&]”hÅhÆuh1jñ  h³hÇh´MPhj0  h²hubhŒnote”“”)”}”(hŒ9Everything in the description above is greatly simplified”h]”j  )”}”(hja  h]”hŒ9Everything in the description above is greatly simplified”…””}”(hjc  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mxhj_  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j]  hj0  h²hh³hÇh´Nubj  )”}”(hŒ¢There are a couple of ways in which to deadlock a FUSE filesystem.
Since we are talking about unprivileged userspace programs,
something must be done about these.”h]”hŒ¢There are a couple of ways in which to deadlock a FUSE filesystem.
Since we are talking about unprivileged userspace programs,
something must be done about these.”…””}”(hjv  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mzhj0  h²hubj  )”}”(hŒ#**Scenario 1 -  Simple deadlock**::”h]”(hŒstrong”“”)”}”(hŒ!**Scenario 1 -  Simple deadlock**”h]”hŒScenario 1 -  Simple deadlock”…””}”(hjŠ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jˆ  hj„  ubhŒ:”…””}”(hj„  h²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M~hj0  h²hubjò  )”}”(hXQ  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
|                                    |
|  >sys_unlink("/mnt/fuse/file")     |
|    [acquire inode semaphore        |
|     for "file"]                    |
|    >fuse_unlink()                  |
|      [sleep on req->waitq]         |
|                                    |  <sys_read()
|                                    |  >sys_unlink("/mnt/fuse/file")
|                                    |    [acquire inode semaphore
|                                    |     for "file"]
|                                    |    *DEADLOCK*”h]”hXQ  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
|                                    |
|  >sys_unlink("/mnt/fuse/file")     |
|    [acquire inode semaphore        |
|     for "file"]                    |
|    >fuse_unlink()                  |
|      [sleep on req->waitq]         |
|                                    |  <sys_read()
|                                    |  >sys_unlink("/mnt/fuse/file")
|                                    |    [acquire inode semaphore
|                                    |     for "file"]
|                                    |    *DEADLOCK*”…””}”hj¢  sbah}”(h]”h ]”h"]”h$]”h&]”hÅhÆuh1jñ  h³hÇh´M€hj0  h²hubj  )”}”(hŒ?The solution for this is to allow the filesystem to be aborted.”h]”hŒ?The solution for this is to allow the filesystem to be aborted.”…””}”(hj°  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mhj0  h²hubj  )”}”(hŒ **Scenario 2 - Tricky deadlock**”h]”j‰  )”}”(hjÀ  h]”hŒScenario 2 - Tricky deadlock”…””}”(hjÂ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jˆ  hj¾  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mhj0  h²hubj  )”}”(hŒ¥This one needs a carefully crafted filesystem.  It's a variation on
the above, only the call back to the filesystem is not explicit,
but is caused by a pagefault. ::”h]”hŒ¤This one needs a carefully crafted filesystem.  Itâ€™s a variation on
the above, only the call back to the filesystem is not explicit,
but is caused by a pagefault.”…””}”(hjÕ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M’hj0  h²hubjò  )”}”(hX  |  Kamikaze filesystem thread 1      |  Kamikaze filesystem thread 2
|                                    |
|  [fd = open("/mnt/fuse/file")]     |  [request served normally]
|  [mmap fd to 'addr']               |
|  [close fd]                        |  [FLUSH triggers 'magic' flag]
|  [read a byte from addr]           |
|    >do_page_fault()                |
|      [find or create page]         |
|      [lock page]                   |
|      >fuse_readpage()              |
|         [queue READ request]       |
|         [sleep on req->waitq]      |
|                                    |  [read request to buffer]
|                                    |  [create reply header before addr]
|                                    |  >sys_write(addr - headerlength)
|                                    |    >fuse_dev_write()
|                                    |      [look up req in fc->processing]
|                                    |      [remove from fc->processing]
|                                    |      [copy write buffer to req]
|                                    |        >do_page_fault()
|                                    |           [find or create page]
|                                    |           [lock page]
|                                    |           * DEADLOCK *”h]”hX  |  Kamikaze filesystem thread 1      |  Kamikaze filesystem thread 2
|                                    |
|  [fd = open("/mnt/fuse/file")]     |  [request served normally]
|  [mmap fd to 'addr']               |
|  [close fd]                        |  [FLUSH triggers 'magic' flag]
|  [read a byte from addr]           |
|    >do_page_fault()                |
|      [find or create page]         |
|      [lock page]                   |
|      >fuse_readpage()              |
|         [queue READ request]       |
|         [sleep on req->waitq]      |
|                                    |  [read request to buffer]
|                                    |  [create reply header before addr]
|                                    |  >sys_write(addr - headerlength)
|                                    |    >fuse_dev_write()
|                                    |      [look up req in fc->processing]
|                                    |      [remove from fc->processing]
|                                    |      [copy write buffer to req]
|                                    |        >do_page_fault()
|                                    |           [find or create page]
|                                    |           [lock page]
|                                    |           * DEADLOCK *”…””}”hjã  sbah}”(h]”h ]”h"]”h$]”h&]”hÅhÆuh1jñ  h³hÇh´M–hj0  h²hubj  )”}”(hŒ,The solution is basically the same as above.”h]”hŒ,The solution is basically the same as above.”…””}”(hjñ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M®hj0  h²hubj  )”}”(hŒçAn additional problem is that while the write buffer is being copied
to the request, the request must not be interrupted/aborted.  This is
because the destination address of the copy may not be valid after the
request has returned.”h]”hŒçAn additional problem is that while the write buffer is being copied
to the request, the request must not be interrupted/aborted.  This is
because the destination address of the copy may not be valid after the
request has returned.”…””}”(hjÿ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´M°hj0  h²hubj  )”}”(hX  This is solved with doing the copy atomically, and allowing abort
while the page(s) belonging to the write buffer are faulted with
get_user_pages().  The 'req->locked' flag indicates when the copy is
taking place, and abort is delayed until this flag is unset.”h]”hX  This is solved with doing the copy atomically, and allowing abort
while the page(s) belonging to the write buffer are faulted with
get_user_pages().  The â€˜req->lockedâ€™ flag indicates when the copy is
taking place, and abort is delayed until this flag is unset.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  h³hÇh´Mµhj0  h²hubeh}”(h]”Œkernel-userspace-interface”ah ]”h"]”Œkernel - userspace interface”ah$]”h&]”uh1hÈhhÊh²hh³hÇh´MJubeh}”(h]”Œfuse-overview”ah ]”h"]”Œfuse overview”ah$]”h&]”uh1hÈhhh²hh³hÇh´Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”hÇuh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(hÍNŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”jN  Œerror_encoding”Œutf-8”Œerror_encoding_error_handler”Œbackslashreplace”Œlanguage_code”Œen”Œrecord_dependencies”NŒconfig”NŒ	id_prefix”hŒauto_id_prefix”Œid”Œdump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”hÇŒ_destination”NŒ_config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒfile_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œpep_references”NŒpep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒrfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ	tab_width”KŒtrim_footnote_reference_space”‰Œsyntax_highlight”Œlong”Œsmart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œdocinfo_xform”KŒsectsubtitle_xform”‰Œimage_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”Œnameids”}”(j(  j%  j4  j1  j›  j˜  j‹  jˆ  j5  j2  jÏ  jÌ  j)  j&  j!  j  jT  jQ  jå  jâ  j•
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  jè  j*  j˜
  j  j0  uŒfootnote_refs”}”Œcitation_refs”}”Œautofootnotes”]”Œautofootnote_refs”]”Œsymbol_footnotes”]”Œsymbol_footnote_refs”]”Œ	footnotes”]”Œ	citations”]”Œautofootnote_start”KŒsymbol_footnote_start”K Œ
id_counter”Œcollections”ŒCounter”“”}”…”R”Œparse_messages”]”Œtransform_messages”]”Œtransformer”NŒinclude_log”]”Œ
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