[PATCH 6.4 700/800] fanotify: disallow mount/sb marks on kernel internal pseudo fs

Greg Kroah-Hartman
2023-07-16T20:25:34Z

From: Amir Goldstein <amir73il@gmail.com>

[ Upstream commit 69562eb0bd3e6bb8e522a7b254334e0fb30dff0c ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/notify/fanotify/fanotify_user.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 22fb1cf7e1fc5..f7e11ac763907 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -1623,6 +1623,20 @@ static int fanotify_events_supported(struct fsnotify_group *group,
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;
+
/*
* We shouldn't have allowed setting dirent events and the directory
* flags FAN_ONDIR and FAN_EVENT_ON_CHILD in mask of non-dir inode,
--
2.39.2