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fanotify: disallow mount/sb marks on kernel internal pseudo fs

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commit 69562eb0bd3e6bb8e522a7b254334e0fb30dff0c upstream.

Hopefully, nobody is trying to abuse mount/sb marks for watching all
anonymous pipes/inodes.

I cannot think of a good reason to allow this - it looks like an
oversight that dated back to the original fanotify API.

Link: https://lore.kernel.org/linux-fsdevel/20230628101132.kvchg544mczxv2pm@quack3/
Fixes: 0ff21db9fcc3 ("fanotify: hooks the fanotify_mark syscall to the vfsmount code")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230629042044.25723-1-amir73il@gmail.com>
[backport to 5.x.y]
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Amir Goldstein 2023-06-29 07:20:44 +03:00 committed by Greg Kroah-Hartman
parent 5cb46b80ec
commit 5bf73af8b3
1 changed files with 20 additions and 2 deletions
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22
fs/notify/fanotify/fanotify_user.c
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@ -1090,8 +1090,11 @@ static int fanotify_test_fid(struct path *path, __kernel_fsid_t *fsid)
return 0;
}
static int fanotify_events_supported(struct path *path, __u64 mask)
static int fanotify_events_supported(struct path *path, __u64 mask,
unsigned int flags)
{
unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
/*
* Some filesystems such as 'proc' acquire unusual locks when opening
* files. For them fanotify permission events have high chances of
@ -1103,6 +1106,21 @@ static int fanotify_events_supported(struct path *path, __u64 mask)
if (mask & FANOTIFY_PERM_EVENTS &&
path->mnt->mnt_sb->s_type->fs_flags & FS_DISALLOW_NOTIFY_PERM)
return -EINVAL;
/*
* mount and sb marks are not allowed on kernel internal pseudo fs,
* like pipe_mnt, because that would subscribe to events on all the
* anonynous pipes in the system.
*
* SB_NOUSER covers all of the internal pseudo fs whose objects are not
* exposed to user's mount namespace, but there are other SB_KERNMOUNT
* fs, like nsfs, debugfs, for which the value of allowing sb and mount
* mark is questionable. For now we leave them alone.
*/
if (mark_type != FAN_MARK_INODE &&
path->mnt->mnt_sb->s_flags & SB_NOUSER)
return -EINVAL;
return 0;
}
@ -1218,7 +1236,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
goto fput_and_out;
if (flags & FAN_MARK_ADD) {
ret = fanotify_events_supported(&path, mask);
ret = fanotify_events_supported(&path, mask, flags);
if (ret)
goto path_put_and_out;
}