From	Quentin Casasnovas <>
Subject	[PATCH] RDS: fix race condition when sending a message on unbound socket.
Date	Fri, 16 Oct 2015 17:11:42 +0200
	

Sasha's found a NULL pointer dereference in the RDS connection code when
sending a message to an apparently unbound socket.  The problem is caused
by the code checking if the socket is bound in rds_sendmsg(), which checks
the rs_bound_addr field without taking a lock on the socket.  This opens a
race where rs_bound_addr is temporarily set but where the transport is not
in rds_bind(), leading to a NULL pointer dereference when trying to
dereference 'trans' in __rds_conn_create().

Vegard wrote a reproducer for this issue, so kindly ask him to share if
you're interested.

I cannot reproduce the NULL pointer dereference using Vegard's reproducer
with this patch, whereas I could without.

Complete earlier incomplete fix to CVE-2015-6937:

  74e98eb08588 ("RDS: verify the underlying transport exists before creating a connection")

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
Reviewed-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Chien Yen <chien.yen@oracle.com>
Cc: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: stable@vger.kernel.org
---
diff -ru a/net/rds/send.c b/net/rds/send.c
--- a/net/rds/send.c	2015-08-30 11:34:09.000000000 -0700
+++ b/net/rds/send.c	2016-02-03 15:10:09.535283384 -0800
@@ -986,11 +986,13 @@
 		release_sock(sk);
 	}
 
-	/* racing with another thread binding seems ok here */
+        lock_sock(sk);
 	if (daddr == 0 || rs->rs_bound_addr == 0) {
+                release_sock(sk);
 		ret = -ENOTCONN; /* XXX not a great errno */
 		goto out;
 	}
+        release_sock(sk);
 
 	/* size of rm including all sgs */
 	ret = rds_rm_size(msg, payload_len);
-- 
2.4.9