This is a note to let you know that I've just added the patch titled

vfs: don't do RCU lookup of empty pathnames

to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: vfs-don-t-do-rcu-lookup-of-empty-pathnames.patch and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From c0eb027e5aef70b71e5a38ee3e264dc0b497f343 Mon Sep 17 00:00:00 2001

From: Linus Torvalds torvalds@linux-foundation.org Date: Sun, 2 Apr 2017 17:10:08 -0700 Subject: vfs: don't do RCU lookup of empty pathnames

From: Linus Torvalds torvalds@linux-foundation.org

commit c0eb027e5aef70b71e5a38ee3e264dc0b497f343 upstream.

Normal pathname lookup doesn't allow empty pathnames, but using AT_EMPTY_PATH (with name_to_handle_at() or fstatat(), for example) you can trigger an empty pathname lookup.

And not only is the RCU lookup in that case entirely unnecessary (because we'll obviously immediately finalize the end result), it is actively wrong.

Why? An empth path is a special case that will return the original 'dirfd' dentry - and that dentry may not actually be RCU-free'd, resulting in a potential use-after-free if we were to initialize the path lazily under the RCU read lock and depend on complete_walk() finalizing the dentry.

Found by syzkaller and KASAN.

Reported-by: Dmitry Vyukov dvyukov@google.com Reported-by: Vegard Nossum vegard.nossum@gmail.com Acked-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Cc: Eric Biggers ebiggers3@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- fs/namei.c | 3 +++ 1 file changed, 3 insertions(+)

--- a/fs/namei.c +++ b/fs/namei.c @@ -1851,6 +1851,9 @@ static int path_init(int dfd, const char { int retval = 0;

+ if (!*s) + flags &= ~LOOKUP_RCU; + nd->last_type = LAST_ROOT; /* if there are only slashes... */ nd->flags = flags | LOOKUP_JUMPED; nd->depth = 0;

Patches currently in stable-queue which might be from torvalds@linux-foundation.org are

queue-3.18/vfs-don-t-do-rcu-lookup-of-empty-pathnames.patch