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

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
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>

diff --git a/net/rds/connection.c b/net/rds/connection.c
index d4564036a339a04d31c65ec6c90cdc9e6a051efc..e3b118cae81d5e859e0244df1bf323aaa1798b8e 100644 (file)
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -186,12 +186,6 @@ static struct rds_connection *__rds_conn_create(struct net *net,
                }
        }
 
-       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);

diff --git a/net/rds/send.c b/net/rds/send.c
index 827155c2ead10376cb633c45c2f43917f5f5cd12..c9cdb358ea885e3e356cc675b579f1313ed94ff9 100644 (file)
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -1013,11 +1013,13 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
                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);
 
        if (payload_len > rds_sk_sndbuf(rs)) {
                ret = -EMSGSIZE;