From: Amir Goldstein <amir73il@xxxxxxxxx> 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@xxxxxxxxx> Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx> Signed-off-by: Jan Kara <jack@xxxxxxx> Message-Id: <20230629042044.25723-1-amir73il@xxxxxxxxx> [backport to 5.x.y] Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/notify/fanotify/fanotify_user.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -1090,8 +1090,11 @@ static int fanotify_test_fid(struct path 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(str 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 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; }
