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| author | Piotr Krysiuk <piotras@gmail.com> | 2020-04-27 11:34:12 +0100 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2020-05-22 21:19:10 +0100 |
| commit | 172f22d527862eb5aa9dd767826f5d68562943db (patch) | |
| tree | 9a657099cdf64428460161d44916ac123f5634a1 | |
| parent | 92f17c867833bbfdaced034629afb8e30a19e882 (diff) | |
| download | linux-stable-172f22d527862eb5aa9dd767826f5d68562943db.tar.gz | |
fs/namespace.c: fix mountpoint reference counter race
A race condition between threads updating mountpoint reference counter
affects longterm releases 4.4.220, 4.9.220, 4.14.177 and 4.19.118.
The mountpoint reference counter corruption may occur when:
* one thread increments m_count member of struct mountpoint
[under namespace_sem, but not holding mount_lock]
pivot_root()
* another thread simultaneously decrements the same m_count
[under mount_lock, but not holding namespace_sem]
put_mountpoint()
unhash_mnt()
umount_mnt()
mntput_no_expire()
To fix this race condition, grab mount_lock before updating m_count in
pivot_root().
Reference: CVE-2020-12114
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Piotr Krysiuk <piotras@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | fs/namespace.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/namespace.c b/fs/namespace.c index 5acf789efbab22..8c41f38617dbb8 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2937,8 +2937,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, /* make certain new is below the root */ if (!is_path_reachable(new_mnt, new.dentry, &root)) goto out4; - root_mp->m_count++; /* pin it so it won't go away */ lock_mount_hash(); + root_mp->m_count++; /* pin it so it won't go away */ detach_mnt(new_mnt, &parent_path); detach_mnt(root_mnt, &root_parent); if (root_mnt->mnt.mnt_flags & MNT_LOCKED) { |