unix: correctly track in-flight fds in sending process user_struct

commit 415e3d3e90ce9e18727e8843ae343eda5a58fad6 upstream.

The commit referenced in the Fixes tag incorrectly accounted the number
of in-flight fds over a unix domain socket to the original opener
of the file-descriptor. This allows another process to arbitrary
deplete the original file-openers resource limit for the maximum of
open files. Instead the sending processes and its struct cred should
be credited.

To do so, we add a reference counted struct user_struct pointer to the
scm_fp_list and use it to account for the number of inflight unix fds.

Fixes: 712f4aad406bb1 ("unix: properly account for FDs passed over unix sockets")
Reported-by: David Herrmann <dh.herrmann@gmail.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index f4842f7afaa5..a69bfee1dd27 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -6,8 +6,8 @@
 #include <linux/mutex.h>
 #include <net/sock.h>
 
-extern void unix_inflight(struct file *fp);
-extern void unix_notinflight(struct file *fp);
+extern void unix_inflight(struct user_struct *user, struct file *fp);
+extern void unix_notinflight(struct user_struct *user, struct file *fp);
 extern void unix_gc(void);
 extern void wait_for_unix_gc(void);
 extern struct sock *unix_get_socket(struct file *filp);