RDS: fix race condition when sending a message on unbound socket (CVE-2015-7990)

debian/changelog

@@ -1,6 +1,8 @@
 linux (4.2.5-2) UNRELEASED; urgency=medium
 
   * usbvision: fix overflow of interfaces array (CVE-2015-7833)
+  * RDS: fix race condition when sending a message on unbound socket
+    (CVE-2015-7990)
 
  -- Ben Hutchings <ben@decadent.org.uk>  Sun, 08 Nov 2015 14:47:40 +0000
 

debian/patches/bugfix/all/rds-fix-race-condition-when-sending-a-message-on-unbound-socket.patch

@@ -0,0 +1,69 @@
+From: Quentin Casasnovas <quentin.casasnovas@oracle.com>
+Subject: RDS: fix race condition when sending a message on unbound socket.
+Date: Fri, 16 Oct 2015 17:11:42 +0200
+Origin: https://lkml.org/lkml/2015/10/16/530
+
+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
+---
+ net/rds/connection.c | 6 ------
+ net/rds/send.c       | 4 +++-
+ 2 files changed, 3 insertions(+), 7 deletions(-)
+
+--- a/net/rds/connection.c
++++ b/net/rds/connection.c
+@@ -187,12 +187,6 @@ new_conn:
+ 		}
+ 	}
+ 
+-	if (trans == NULL) {
+-		kmem_cache_free(rds_conn_slab, conn);
+-		conn = ERR_PTR(-ENODEV);
+-		goto out;
+-	}
+-
+ 	conn->c_trans = trans;
+ 
+ 	ret = trans->conn_alloc(conn, gfp);
+--- a/net/rds/send.c
++++ b/net/rds/send.c
+@@ -986,11 +986,13 @@ int rds_sendmsg(struct socket *sock, str
+ 		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);

debian/patches/series

@@ -105,3 +105,4 @@ bugfix/all/KEYS-Don-t-permit-request_key-to-construct-a-new-key.patch
 debian/target-fix-abi-change-in-4.2.4.patch
 debian/signal-fix-abi-change-in-4.2.4.patch
 bugfix/all/usbvision-fix-overflow-of-interfaces-array.patch
+bugfix/all/rds-fix-race-condition-when-sending-a-message-on-unbound-socket.patch