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fanotify: limit reporting of event with non-decodeable file handles

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Commit a95aef69a7 ("fanotify: support reporting non-decodeable file
handles") merged in v6.5-rc1, added the ability to use an fanotify group
with FAN_REPORT_FID mode to watch filesystems that do not support nfs
export, but do know how to encode non-decodeable file handles, with the
newly introduced AT_HANDLE_FID flag.

At the time that this commit was merged, there were no filesystems
in-tree with those traits.

Commit 16aac5ad1f ("ovl: support encoding non-decodable file handles"),
merged in v6.6-rc1, added this trait to overlayfs, thus allowing fanotify
watching of overlayfs with FAN_REPORT_FID mode.

In retrospect, allowing an fanotify filesystem/mount mark on such
filesystem in FAN_REPORT_FID mode will result in getting events with
file handles, without the ability to resolve the filesystem objects from
those file handles (i.e. no open_by_handle_at() support).

For v6.6, the safer option would be to allow this mode for inode marks
only, where the caller has the opportunity to use name_to_handle_at() at
the time of setting the mark. In the future we can revise this decision.

Fixes: a95aef69a7 ("fanotify: support reporting non-decodeable file handles")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20231018100000.2453965-2-amir73il@gmail.com>
This commit is contained in:
Amir Goldstein 2023-10-18 12:59:56 +03:00 committed by Jan Kara
parent dd72f9c7e5
commit 97ac489775
1 changed files with 17 additions and 8 deletions
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25
fs/notify/fanotify/fanotify_user.c
View File

@ -1585,16 +1585,25 @@ static int fanotify_test_fsid(struct dentry *dentry, __kernel_fsid_t *fsid)
}
/* Check if filesystem can encode a unique fid */
static int fanotify_test_fid(struct dentry *dentry)
static int fanotify_test_fid(struct dentry *dentry, unsigned int flags)
{
unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
const struct export_operations *nop = dentry->d_sb->s_export_op;
/*
* We need to make sure that the file system supports at least
* encoding a file handle so user can use name_to_handle_at() to
* compare fid returned with event to the file handle of watched
* objects. However, even the relaxed AT_HANDLE_FID flag requires
* at least empty export_operations for ecoding unique file ids.
* We need to make sure that the filesystem supports encoding of
* file handles so user can use name_to_handle_at() to compare fids
* reported with events to the file handle of watched objects.
*/
if (!dentry->d_sb->s_export_op)
if (!nop)
return -EOPNOTSUPP;
/*
* For sb/mount mark, we also need to make sure that the filesystem
* supports decoding file handles, so user has a way to map back the
* reported fids to filesystem objects.
*/
if (mark_type != FAN_MARK_INODE && !nop->fh_to_dentry)
return -EOPNOTSUPP;
return 0;
@ -1812,7 +1821,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
if (ret)
goto path_put_and_out;
ret = fanotify_test_fid(path.dentry);
ret = fanotify_test_fid(path.dentry, flags);
if (ret)
goto path_put_and_out;