RDS: fix race condition when sending a message on unbound socket

[ Upstream commit 8c7188b23474cca017b3ef354c4a58456f68303a ]

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")

Cc: David S. Miller <davem@davemloft.net>
Cc: stable@vger.kernel.org
Change-Id: I7b41743a51bd3213de624d6165c6366c9f808067
Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
Reviewed-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
[mainline backport of commit 96c7b10cd8000973035b667adf62ea1164f4b9b4]
Change-Id: I7b41743a51bd3213de624d6165c6366c9f808067
Signed-off-by: Jaechul Lee <jcsing.lee@samsung.com>

diff --git a/net/rds/send.c b/net/rds/send.c
index 0a64541020b0b52edb0cf197a55ff12cc36ccb8e..0bae8d43b0127a5c819755264d0afde918b7ab60 100644 (file)
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -958,11 +958,13 @@ int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
                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);