€•O      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$/translations/zh_CN/filesystems/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ$/translations/zh_TW/filesystems/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ$/translations/it_IT/filesystems/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ$/translations/ja_JP/filesystems/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ$/translations/ko_KR/filesystems/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ$/translations/sp_SP/filesystems/fuse”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”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$]”h&]”Œ	xml:space”Œpreserve”uh1h¡hhhžhhŸŒ>/var/lib/git/docbuild/linux/Documentation/filesystems/fuse.rst”h KubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒFUSE”h]”hŒFUSE”…””}”(hh»hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒDefinitions”h]”hŒDefinitions”…””}”(hhÌhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hhÉhžhhŸh³h KubhŒdefinition_list”“”)”}”(hhh]”(hŒdefinition_list_item”“”)”}”(hŒ´Userspace filesystem:
A filesystem in which data and metadata are provided by an ordinary
userspace process.  The filesystem can be accessed normally through
the kernel interface.
”h]”(hŒterm”“”)”}”(hŒUserspace filesystem:”h]”hŒUserspace filesystem:”…””}”(hhçhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h Khháubh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hühžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Khh÷ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhháubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KhhÜubhà)”}”(hŒVFilesystem daemon:
The process(es) providing the data and metadata of the filesystem.
”h]”(hæ)”}”(hŒFilesystem daemon:”h]”hŒFilesystem daemon:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h Khj  ubhö)”}”(hhh]”hû)”}”(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+  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Khj(  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KhhÜhžhubhà)”}”(hX&  Non-privileged mount (or user mount):
A userspace filesystem mounted by a non-privileged (non-root) user.
The filesystem daemon is running with the privileges of the mounting
user.  NOTE: this is not the same as mounts allowed with the "user"
option in /etc/fstab, which is not discussed here.
”h]”(hæ)”}”(hŒ%Non-privileged mount (or user mount):”h]”hŒ%Non-privileged mount (or user mount):”…””}”(hjI  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h KhjE  ubhö)”}”(hhh]”hû)”}”(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jZ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KhjW  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjE  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KhhÜhžhubhà)”}”(hXR  Filesystem connection:
A connection between the filesystem daemon and the kernel.  The
connection exists until either the daemon dies, or the filesystem is
umounted.  Note that detaching (or lazy umounting) the filesystem
does *not* break the connection, in this case it will exist until
the last reference to the filesystem is released.
”h]”(hæ)”}”(hŒFilesystem connection:”h]”hŒFilesystem connection:”…””}”(hjx  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h Khjt  ubhö)”}”(hhh]”hû)”}”(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‰  hžhhŸNh NubhŒemphasis”“”)”}”(hŒ*not*”h]”hŒnot”…””}”(hj“  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‘  hj‰  ubhŒi break the connection, in this case it will exist until
the last reference to the filesystem is released.”…””}”(hj‰  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Khj†  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjt  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KhhÜhžhubhà)”}”(hŒ-Mount owner:
The user who does the mounting.
”h]”(hæ)”}”(hŒMount owner:”h]”hŒMount owner:”…””}”(hj»  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h K hj·  ubhö)”}”(hhh]”hû)”}”(hŒThe user who does the mounting.”h]”hŒThe user who does the mounting.”…””}”(hjÌ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K hjÉ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj·  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h K hhÜhžhubhà)”}”(hŒ8User:
The user who is performing filesystem operations.
”h]”(hæ)”}”(hŒUser:”h]”hŒUser:”…””}”(hjê  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h K#hjæ  ubhö)”}”(hhh]”hû)”}”(hŒ1The user who is performing filesystem operations.”h]”hŒ1The user who is performing filesystem operations.”…””}”(hjû  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K#hjø  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjæ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h K#hhÜhžhubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhhÉhžhhŸh³h Nubeh}”(h]”Œdefinitions”ah ]”h"]”Œdefinitions”ah$]”h&]”uh1h´hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒWhat is FUSE?”h]”hŒWhat is FUSE?”…””}”(hj&  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj#  hžhhŸh³h K&ubhû)”}”(hŒ–FUSE is a userspace filesystem framework.  It consists of a kernel
module (fuse.ko), a userspace library (libfuse.*) and a mount utility
(fusermount).”h]”hŒ–FUSE is a userspace filesystem framework.  It consists of a kernel
module (fuse.ko), a userspace library (libfuse.*) and a mount utility
(fusermount).”…””}”(hj4  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K(hj#  hžhubhû)”}”(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jB  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K,hj#  hžhubhû)”}”(hŒjThe userspace library and utilities are available from the
`FUSE homepage: <https://github.com/libfuse/>`_”h]”(hŒ;The userspace library and utilities are available from the
”…””}”(hjP  hžhhŸNh NubhŒ	reference”“”)”}”(hŒ/`FUSE homepage: <https://github.com/libfuse/>`_”h]”hŒFUSE homepage:”…””}”(hjZ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œname”ŒFUSE homepage:”Œrefuri”Œhttps://github.com/libfuse/”uh1jX  hjP  ubhŒtarget”“”)”}”(hŒ <https://github.com/libfuse/>”h]”h}”(h]”Œfuse-homepage”ah ]”h"]”Œfuse homepage:”ah$]”h&]”Œrefuri”jk  uh1jl  Œ
referenced”KhjP  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K1hj#  hžhubeh}”(h]”Œwhat-is-fuse”ah ]”h"]”Œwhat is fuse?”ah$]”h&]”uh1h´hh¶hžhhŸh³h K&ubhµ)”}”(hhh]”(hº)”}”(hŒFilesystem type”h]”hŒFilesystem type”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjŠ  hžhhŸh³h K5ubhû)”}”(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›  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K7hjŠ  hžhubh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]”hÛ)”}”(hhh]”(hà)”}”(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]”(hæ)”}”(hŒfuse”h]”hŒfuse”…””}”(hj¶  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h K<hj²  ubhö)”}”(hhh]”hû)”}”(hŒ§This is the usual way to mount a FUSE filesystem.  The first
argument of the mount system call may contain an arbitrary string,
which is not interpreted by the kernel.”h]”hŒ§This is the usual way to mount a FUSE filesystem.  The first
argument of the mount system call may contain an arbitrary string,
which is not interpreted by the kernel.”…””}”(hjÇ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K:hjÄ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj²  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h K<hj¯  ubhà)”}”(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]”(hæ)”}”(hŒfuseblk”h]”hŒfuseblk”…””}”(hjå  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h K@hjá  ubhö)”}”(hhh]”hû)”}”(hŒ|The filesystem is block device based.  The first argument of the
mount system call is interpreted as the name of the device.”h]”hŒ|The filesystem is block device based.  The first argument of the
mount system call is interpreted as the name of the device.”…””}”(hjö  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K?hjó  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjá  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h K@hj¯  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhj«  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h K9hjŠ  hžhubeh}”(h]”Œfilesystem-type”ah ]”h"]”Œfilesystem type”ah$]”h&]”uh1h´hh¶hžhhŸh³h K5ubhµ)”}”(hhh]”(hº)”}”(hŒMount options”h]”hŒMount options”…””}”(hj'  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj$  hžhhŸh³h KCubhÛ)”}”(hhh]”(hà)”}”(hŒºfd=N
The file descriptor to use for communication between the userspace
filesystem and the kernel.  The file descriptor must have been
obtained by opening the FUSE device ('/dev/fuse').
”h]”(hæ)”}”(hŒfd=N”h]”hŒfd=N”…””}”(hj<  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h KHhj8  ubhö)”}”(hhh]”hû)”}”(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jM  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KFhjJ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj8  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KHhj5  ubhà)”}”(hŒKrootmode=M
The file mode of the filesystem's root in octal representation.
”h]”(hæ)”}”(hŒ
rootmode=M”h]”hŒ
rootmode=M”…””}”(hjk  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h KKhjg  ubhö)”}”(hhh]”hû)”}”(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|  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KKhjy  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjg  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KKhj5  hžhubhà)”}”(hŒ2user_id=N
The numeric user id of the mount owner.
”h]”(hæ)”}”(hŒ	user_id=N”h]”hŒ	user_id=N”…””}”(hjš  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h KNhj–  ubhö)”}”(hhh]”hû)”}”(hŒ'The numeric user id of the mount owner.”h]”hŒ'The numeric user id of the mount owner.”…””}”(hj«  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KNhj¨  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj–  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KNhj5  hžhubhà)”}”(hŒ4group_id=N
The numeric group id of the mount owner.
”h]”(hæ)”}”(hŒ
group_id=N”h]”hŒ
group_id=N”…””}”(hjÉ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h KQhjÅ  ubhö)”}”(hhh]”hû)”}”(hŒ(The numeric group id of the mount owner.”h]”hŒ(The numeric group id of the mount owner.”…””}”(hjÚ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KQhj×  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjÅ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KQhj5  hžhubhà)”}”(hXq  default_permissions
By default FUSE doesn't check file access permissions, the
filesystem is free to implement its access policy or leave it to
the underlying file access mechanism (e.g. in case of network
filesystems).  This option enables permission checking, restricting
access based on file mode.  It is usually useful together with the
'allow_other' mount option.
”h]”(hæ)”}”(hŒdefault_permissions”h]”hŒdefault_permissions”…””}”(hjø  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h KYhjô  ubhö)”}”(hhh]”hû)”}”(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	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KThj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjô  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h KYhj5  hžhubhà)”}”(hŒòallow_other
This option overrides the security measure restricting file access
to the user mounting the filesystem.  This option is by default only
allowed to root, but this restriction can be removed with a
(userspace) configuration option.
”h]”(hæ)”}”(hŒallow_other”h]”hŒallow_other”…””}”(hj'  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h K_hj#  ubhö)”}”(hhh]”hû)”}”(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j8  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K\hj5  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj#  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h K_hj5  hžhubhà)”}”(hŒÅmax_read=N
With this option the maximum size of read operations can be set.
The default is infinite.  Note that the size of read requests is
limited anyway to 32 pages (which is 128kbyte on i386).
”h]”(hæ)”}”(hŒ
max_read=N”h]”hŒ
max_read=N”…””}”(hjV  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h KdhjR  ubhö)”}”(hhh]”hû)”}”(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jg  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kbhjd  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjR  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h Kdhj5  hžhubhà)”}”(hŒ|blksize=N
Set the block size for the filesystem.  The default is 512.  This
option is only valid for 'fuseblk' type mounts.
”h]”(hæ)”}”(hŒ	blksize=N”h]”hŒ	blksize=N”…””}”(hj…  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h Khhj  ubhö)”}”(hhh]”hû)”}”(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j–  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kghj“  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h Khhj5  hžhubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhj$  hžhhŸh³h Nubeh}”(h]”Œmount-options”ah ]”h"]”Œmount options”ah$]”h&]”uh1h´hh¶hžhhŸh³h KCubhµ)”}”(hhh]”(hº)”}”(hŒControl filesystem”h]”hŒControl filesystem”…””}”(hjÁ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj¾  hžhhŸh³h Kkubhû)”}”(hŒ@There's a control filesystem for FUSE, which can be mounted by::”h]”hŒAThereâ€™s a control filesystem for FUSE, which can be mounted by:”…””}”(hjÏ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kmhj¾  hžhubh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jß  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jÝ  hŸh³h Kohj¾  hžhubhû)”}”(hŒoMounting it under the '/sys/fs/fuse/connections' directory makes it
backwards compatible with earlier versions.”h]”hŒsMounting it under the â€˜/sys/fs/fuse/connectionsâ€™ directory makes it
backwards compatible with earlier versions.”…””}”(hjí  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kqhj¾  hžhubhû)”}”(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jû  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kthj¾  hžhubhû)”}”(hŒDFor each connection the following files exist within this directory:”h]”hŒDFor each connection the following files exist within this directory:”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kwhj¾  hžhubjª  )”}”(hX¬  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.
”h]”hÛ)”}”(hhh]”(hà)”}”(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]”(hæ)”}”(hŒwaiting”h]”hŒwaiting”…””}”(hj"  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h K}hj  ubhö)”}”(hhh]”hû)”}”(hŒÞThe number of requests which are waiting to be transferred to
userspace or being processed by the filesystem daemon.  If there is
no filesystem activity and 'waiting' is non-zero, then the
filesystem is hung or deadlocked.”h]”hŒâThe number of requests which are waiting to be transferred to
userspace or being processed by the filesystem daemon.  If there is
no filesystem activity and â€˜waitingâ€™ is non-zero, then the
filesystem is hung or deadlocked.”…””}”(hj3  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kzhj0  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h K}hj  ubhà)”}”(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]”(hæ)”}”(hŒabort”h]”hŒabort”…””}”(hjQ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1håhŸh³h K‚hjM  ubhö)”}”(hhh]”hû)”}”(hŒ¯Writing anything into this file will abort the filesystem
connection.  This means that all waiting requests will be aborted an
error returned for all aborted and new requests.”h]”hŒ¯Writing anything into this file will abort the filesystem
connection.  This means that all waiting requests will be aborted an
error returned for all aborted and new requests.”…””}”(hjb  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K€hj_  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hõhjM  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hßhŸh³h K‚hj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÚhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h Kyhj¾  hžhubhû)”}”(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jˆ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K„hj¾  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ"Interrupting filesystem operations”h]”hŒ"Interrupting filesystem operations”…””}”(hj™  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj–  hžhhŸh³h K‡ubhû)”}”(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§  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K‰hj–  hžhubjª  )”}”(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]”hû)”}”(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jÄ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KŒhjÀ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj»  ubj¿  )”}”(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]”hû)”}”(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jÜ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KhjØ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj»  ubj¿  )”}”(hŒRIf the request is already sent to userspace, then an INTERRUPT
request is queued.
”h]”hû)”}”(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jô  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K•hjð  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj»  ubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1j¹  hŸh³h KŒhjµ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h KŒhj–  hžhubhû)”}”(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j  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K˜hj–  hžhubhû)”}”(hŒ¡The userspace filesystem may ignore the INTERRUPT requests entirely,
or may honor them by sending a reply to the *original* request, with
the error set to EINTR.”h]”(hŒqThe userspace filesystem may ignore the INTERRUPT requests entirely,
or may honor them by sending a reply to the ”…””}”(hj$  hžhhŸNh Nubj’  )”}”(hŒ
*original*”h]”hŒoriginal”…””}”(hj,  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‘  hj$  ubhŒ& request, with
the error set to EINTR.”…””}”(hj$  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K›hj–  hžhubhû)”}”(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jD  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KŸhj–  hžhubjª  )”}”(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]”(j¿  )”}”(hŒLThe INTERRUPT request is processed before the original request is
processed
”h]”hû)”}”(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j_  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K¢hj[  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjX  ubj¿  )”}”(hŒPThe INTERRUPT request is processed after the original request has
been answered
”h]”hû)”}”(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jw  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K¥hjs  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjX  ubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ.”uh1jV  hjR  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h K¢hj–  hžhubhû)”}”(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jœ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K¨hj–  hžhubeh}”(h]”Œ"interrupting-filesystem-operations”ah ]”h"]”Œ"interrupting filesystem operations”ah$]”h&]”uh1h´hj¾  hžhhŸh³h K‡ubeh}”(h]”Œcontrol-filesystem”ah ]”h"]”Œcontrol filesystem”ah$]”h&]”uh1h´hh¶hžhhŸh³h Kkubhµ)”}”(hhh]”(hº)”}”(hŒ Aborting a filesystem connection”h]”hŒ Aborting a filesystem connection”…””}”(hj½  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjº  hžhhŸh³h K¯ubhû)”}”(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jË  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K±hjº  hžhubjª  )”}”(hŒya) Broken userspace filesystem implementation

b) Network connection down

c) Accidental deadlock

d) Malicious deadlock
”h]”jW  )”}”(hhh]”(j¿  )”}”(hŒ+Broken userspace filesystem implementation
”h]”hû)”}”(hŒ*Broken userspace filesystem implementation”h]”hŒ*Broken userspace filesystem implementation”…””}”(hjä  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K´hjà  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjÝ  ubj¿  )”}”(hŒNetwork connection down
”h]”hû)”}”(hŒNetwork connection down”h]”hŒNetwork connection down”…””}”(hjü  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K¶hjø  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjÝ  ubj¿  )”}”(hŒAccidental deadlock
”h]”hû)”}”(hŒAccidental deadlock”h]”hŒAccidental deadlock”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K¸hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjÝ  ubj¿  )”}”(hŒMalicious deadlock
”h]”hû)”}”(hŒMalicious deadlock”h]”hŒMalicious deadlock”…””}”(hj,  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kºhj(  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjÝ  ubeh}”(h]”h ]”h"]”h$]”h&]”j‘  Œ
loweralpha”j“  hj”  Œ)”uh1jV  hjÙ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h K´hjº  hžhubhû)”}”(hŒ*(For more on c) and d) see later sections)”h]”hŒ*(For more on c) and d) see later sections)”…””}”(hjN  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K¼hjº  hžhubhû)”}”(hŒxIn either of these cases it may be useful to abort the connection to
the filesystem.  There are several ways to do this:”h]”hŒxIn either of these cases it may be useful to abort the connection to
the filesystem.  There are several ways to do this:”…””}”(hj\  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h K¾hjº  hžhubjª  )”}”(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]”jº  )”}”(hhh]”(j¿  )”}”(hŒ8Kill the filesystem daemon.  Works in case of a) and b)
”h]”hû)”}”(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ju  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÁhjq  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjn  ubj¿  )”}”(hŒpKill the filesystem daemon and all users of the filesystem.  Works
in all cases except some malicious deadlocks
”h]”hû)”}”(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j  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÃhj‰  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjn  ubj¿  )”}”(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]”hû)”}”(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¥  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÆhj¡  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjn  ubj¿  )”}”(hŒ[Abort filesystem through the FUSE control filesystem.  Most
powerful method, always works.
”h]”hû)”}”(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j½  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÉhj¹  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjn  ubeh}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j¹  hŸh³h KÁhjj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h KÁhjº  hžhubeh}”(h]”Œ aborting-a-filesystem-connection”ah ]”h"]”Œ aborting a filesystem connection”ah$]”h&]”uh1h´hh¶hžhhŸh³h K¯ubhµ)”}”(hhh]”(hº)”}”(hŒ"How do non-privileged mounts work?”h]”hŒ"How do non-privileged mounts work?”…””}”(hjè  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjå  hžhhŸh³h KÍubhû)”}”(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jö  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÏhjå  hžhubhû)”}”(hŒ¹The implication of providing non-privileged mounts is that the mount
owner must not be able to use this capability to compromise the
system.  Obvious requirements arising from this are:”h]”hŒ¹The implication of providing non-privileged mounts is that the mount
owner must not be able to use this capability to compromise the
system.  Obvious requirements arising from this are:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÒhjå  hžhubjª  )”}”(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]”jW  )”}”(hhh]”(j¿  )”}”(hŒbmount owner should not be able to get elevated privileges with the
help of the mounted filesystem
”h]”hû)”}”(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  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÖhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj  ubj¿  )”}”(hŒomount owner should not get illegitimate access to information from
other users' and the super user's processes
”h]”hû)”}”(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j5  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÙhj1  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj  ubj¿  )”}”(hŒjmount owner should not be able to induce undesired behavior in
other users' or the super user's processes
”h]”hû)”}”(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jM  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KÜhjI  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj  ubeh}”(h]”h ]”h"]”h$]”h&]”j‘  Œ
upperalpha”j“  hj”  jG  uh1jV  hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h KÖhjå  hžhubeh}”(h]”Œ!how-do-non-privileged-mounts-work”ah ]”h"]”Œ"how do non-privileged mounts work?”ah$]”h&]”uh1h´hh¶hžhhŸh³h KÍubhµ)”}”(hhh]”(hº)”}”(hŒHow are requirements fulfilled?”h]”hŒHow are requirements fulfilled?”…””}”(hjy  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjv  hžhhŸh³h Kàubjª  )”}”(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]”jW  )”}”(hhh]”(j¿  )”}”(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]”(hû)”}”(hŒ9The mount owner could gain elevated privileges by either:”h]”hŒ9The mount owner could gain elevated privileges by either:”…””}”(hj’  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KâhjŽ  ubjW  )”}”(hhh]”(j¿  )”}”(hŒIcreating a filesystem containing a device file, then opening this device
”h]”hû)”}”(hŒHcreating a filesystem containing a device file, then opening this device”h]”hŒHcreating a filesystem containing a device file, then opening this device”…””}”(hj§  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kähj£  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj   ubj¿  )”}”(hŒ]creating a filesystem containing a suid or sgid application, then executing this application
”h]”hû)”}”(hŒ\creating a filesystem containing a suid or sgid application, then executing this application”h]”hŒ\creating a filesystem containing a suid or sgid application, then executing this application”…””}”(hj¿  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kæhj»  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj   ubeh}”(h]”h ]”h"]”h$]”h&]”j‘  j’  j“  hj”  j•  uh1jV  hjŽ  ubhû)”}”(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jÙ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h KèhjŽ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj‹  ubj¿  )”}”(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]”(hû)”}”(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jñ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kíhjí  ubhû)”}”(hŒAThe solution to this problem will be presented in point 2) of C).”h]”hŒAThe solution to this problem will be presented in point 2) of C).”…””}”(hjÿ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kóhjí  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj‹  ubj¿  )”}”(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]”(hû)”}”(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	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kõhj	  ubjª  )”}”(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]”jW  )”}”(hhh]”(j¿  )”}”(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]”(hû)”}”(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j0	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Køhj,	  ubhû)”}”(hŒðThis is solved in fusermount, by checking the access
permissions on the mountpoint and only allowing the mount if
the mount owner can do unlimited modification (has write
access to the mountpoint, and mountpoint is not a "sticky"
directory)”h]”hŒôThis is solved in fusermount, by checking the access
permissions on the mountpoint and only allowing the mount if
the mount owner can do unlimited modification (has write
access to the mountpoint, and mountpoint is not a â€œstickyâ€
directory)”…””}”(hj>	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Kühj,	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj)	  ubj¿  )”}”(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]”(hû)”}”(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jV	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h MhjR	  ubjª  )”}”(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]”jW  )”}”(hh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]”hû)”}”(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jo	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Mhjk	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjh	  ubj¿  )”}”(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]”hû)”}”(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j‡	  hžhhŸNh Nubj’  )”}”(hŒ*DoS*”h]”hŒDoS”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‘  hj‡	  ubhŒ.”…””}”(hj‡	  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Mhjƒ	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjh	  ubeh}”(h]”h ]”h"]”h$]”h&]”j‘  Œ
lowerroman”j“  hj”  jG  uh1jV  hjd	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h MhjR	  ubhû)”}”(hXy  The solution to this as well as B) is not to allow processes
to access the filesystem, which could otherwise not be
monitored or manipulated by the mount owner.  Since if the
mount owner can ptrace a process, it can do all of the above
without using a FUSE mount, the same criteria as used in
ptrace can be used to check if a process is allowed to access
the filesystem or not.”h]”hXy  The solution to this as well as B) is not to allow processes
to access the filesystem, which could otherwise not be
monitored or manipulated by the mount owner.  Since if the
mount owner can ptrace a process, it can do all of the above
without using a FUSE mount, the same criteria as used in
ptrace can be used to check if a process is allowed to access
the filesystem or not.”…””}”(hjº	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h MhjR	  ubhû)”}”(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jÈ	  hžhhŸNh Nubj’  )”}”(hŒ*ptrace*”h]”hŒptrace”…””}”(hjÐ	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‘  hjÈ	  ubhŒ« check is not strictly necessary to
prevent C/2/i, it is enough to check if mount owner has enough
privilege to send signal to the process accessing the
filesystem, since ”…””}”(hjÈ	  hžhhŸNh Nubj’  )”}”(hŒ	*SIGSTOP*”h]”hŒSIGSTOP”…””}”(hjâ	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‘  hjÈ	  ubhŒ% can be used to get a similar effect.”…””}”(hjÈ	  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h MhjR	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj)	  ubeh}”(h]”h ]”h"]”h$]”h&]”j‘  j’  j“  hj”  jG  uh1jV  hj%	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h Køhj	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hj‹  ubeh}”(h]”h ]”h"]”h$]”h&]”j‘  jg  j“  hj”  jG  uh1jV  hj‡  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h Kâhjv  hžhubeh}”(h]”Œhow-are-requirements-fulfilled”ah ]”h"]”Œhow are requirements fulfilled?”ah$]”h&]”uh1h´hh¶hžhhŸh³h Kàubhµ)”}”(hhh]”(hº)”}”(hŒ+I think these limitations are unacceptable?”h]”hŒ+I think these limitations are unacceptable?”…””}”(hj)
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj&
  hžhhŸh³h Mubhû)”}”(hŒ¼If a sysadmin trusts the users enough, or can ensure through other
measures, that system processes will never enter non-privileged
mounts, it can relax the last limitation in several ways:”h]”hŒ¼If a sysadmin trusts the users enough, or can ensure through other
measures, that system processes will never enter non-privileged
mounts, it can relax the last limitation in several ways:”…””}”(hj7
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M!hj&
  hžhubjª  )”}”(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]”jº  )”}”(hhh]”(j¿  )”}”(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]”(hû)”}”(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jP
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M%hjL
  ubhû)”}”(hXÔ  User namespaces have an unintuitive interaction with 'allow_other':
an unprivileged user - normally restricted from mounting with
'allow_other' - could do so in a user namespace where they're
privileged. If any process could access such an 'allow_other' mount
this would give the mounting user the ability to manipulate
processes in user namespaces where they're unprivileged. For this
reason 'allow_other' restricts access to users in the same userns
or a descendant.”h]”hXè  User namespaces have an unintuitive interaction with â€˜allow_otherâ€™:
an unprivileged user - normally restricted from mounting with
â€˜allow_otherâ€™ - could do so in a user namespace where theyâ€™re
privileged. If any process could access such an â€˜allow_otherâ€™ mount
this would give the mounting user the ability to manipulate
processes in user namespaces where theyâ€™re unprivileged. For this
reason â€˜allow_otherâ€™ restricts access to users in the same userns
or a descendant.”…””}”(hj^
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M)hjL
  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjI
  ubj¿  )”}”(hŒÎWith the 'allow_sys_admin_access' module option. If this option is
set, super user's processes have unrestricted access to mounts
irrespective of allow_other setting or user namespace of the
mounting user.
”h]”hû)”}”(hŒÍWith the 'allow_sys_admin_access' module option. If this option is
set, super user's processes have unrestricted access to mounts
irrespective of allow_other setting or user namespace of the
mounting user.”h]”hŒÓWith the â€˜allow_sys_admin_accessâ€™ module option. If this option is
set, super userâ€™s processes have unrestricted access to mounts
irrespective of allow_other setting or user namespace of the
mounting user.”…””}”(hjv
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M2hjr
  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j¾  hjI
  ubeh}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j¹  hŸh³h M%hjE
  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j©  hŸh³h M%hj&
  hžhubhû)”}”(hŒœNote that both of these relaxations expose the system to potential
information leak or *DoS* as described in points B and C/2/i-ii in the
preceding section.”h]”(hŒWNote that both of these relaxations expose the system to potential
information leak or ”…””}”(hj–
  hžhhŸNh Nubj’  )”}”(hŒ*DoS*”h]”hŒDoS”…””}”(hjž
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‘  hj–
  ubhŒ@ as described in points B and C/2/i-ii in the
preceding section.”…””}”(hj–
  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M7hj&
  hžhubeh}”(h]”Œ*i-think-these-limitations-are-unacceptable”ah ]”h"]”Œ+i think these limitations are unacceptable?”ah$]”h&]”uh1h´hh¶hžhhŸh³h Mubhµ)”}”(hhh]”(hº)”}”(hŒKernel - userspace interface”h]”hŒKernel - userspace interface”…””}”(hjÁ
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj¾
  hžhhŸh³h M<ubhû)”}”(hŒhThe following diagram shows how a filesystem operation (in this
example unlink) is performed in FUSE. ::”h]”hŒeThe following diagram shows how a filesystem operation (in this
example unlink) is performed in FUSE.”…””}”(hjÏ
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M>hj¾
  hžhubjÞ  )”}”(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jÝ
  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jÝ  hŸh³h MBhj¾
  hžhubhŒnote”“”)”}”(hŒ9Everything in the description above is greatly simplified”h]”hû)”}”(hjï
  h]”hŒ9Everything in the description above is greatly simplified”…””}”(hjñ
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Mjhjí
  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jë
  hj¾
  hžhhŸh³h Nubhû)”}”(hŒ¢There are a couple of ways in which to deadlock a FUSE filesystem.
Since we are talking about unprivileged userspace programs,
something must be done about these.”•B$      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j  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Mlhj¾
  hžhubhû)”}”(hŒ#**Scenario 1 -  Simple deadlock**::”h]”(hŒstrong”“”)”}”(hŒ!**Scenario 1 -  Simple deadlock**”h]”hŒScenario 1 -  Simple deadlock”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj  ubhŒ:”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Mphj¾
  hžhubjÞ  )”}”(hXQ  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
|                                    |
|  >sys_unlink("/mnt/fuse/file")     |
|    [acquire inode semaphore        |
|     for "file"]                    |
|    >fuse_unlink()                  |
|      [sleep on req->waitq]         |
|                                    |  <sys_read()
|                                    |  >sys_unlink("/mnt/fuse/file")
|                                    |    [acquire inode semaphore
|                                    |     for "file"]
|                                    |    *DEADLOCK*”h]”hXQ  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
|                                    |
|  >sys_unlink("/mnt/fuse/file")     |
|    [acquire inode semaphore        |
|     for "file"]                    |
|    >fuse_unlink()                  |
|      [sleep on req->waitq]         |
|                                    |  <sys_read()
|                                    |  >sys_unlink("/mnt/fuse/file")
|                                    |    [acquire inode semaphore
|                                    |     for "file"]
|                                    |    *DEADLOCK*”…””}”hj0  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jÝ  hŸh³h Mrhj¾
  hžhubhû)”}”(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>  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Mhj¾
  hžhubhû)”}”(hŒ **Scenario 2 - Tricky deadlock**”h]”j  )”}”(hjN  h]”hŒScenario 2 - Tricky deadlock”…””}”(hjP  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjL  ubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h Mhj¾
  hžhubhû)”}”(hŒ¥This one needs a carefully crafted filesystem.  It's a variation on
the above, only the call back to the filesystem is not explicit,
but is caused by a pagefault. ::”h]”hŒ¤This one needs a carefully crafted filesystem.  Itâ€™s a variation on
the above, only the call back to the filesystem is not explicit,
but is caused by a pagefault.”…””}”(hjc  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M„hj¾
  hžhubjÞ  )”}”(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jq  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jÝ  hŸh³h Mˆhj¾
  hžhubhû)”}”(hŒ,The solution is basically the same as above.”h]”hŒ,The solution is basically the same as above.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M hj¾
  hžhubhû)”}”(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j  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M¢hj¾
  hžhubhû)”}”(hX  This is solved with doing the copy atomically, and allowing abort
while the page(s) belonging to the write buffer are faulted with
get_user_pages().  The 'req->locked' flag indicates when the copy is
taking place, and abort is delayed until this flag is unset.”h]”hX  This is solved with doing the copy atomically, and allowing abort
while the page(s) belonging to the write buffer are faulted with
get_user_pages().  The â€˜req->lockedâ€™ flag indicates when the copy is
taking place, and abort is delayed until this flag is unset.”…””}”(hj›  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1húhŸh³h M§hj¾
  hžhubeh}”(h]”Œkernel-userspace-interface”ah ]”h"]”Œkernel - userspace interface”ah$]”h&]”uh1h´hh¶hžhhŸh³h M<ubeh}”(h]”Œfuse”ah ]”h"]”Œfuse”ah$]”h&]”uh1h´hhhžhhŸh³h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h³uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¹NŒ	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
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