Commit 8c7188b2 authored Nov 24, 2015 by Quentin Casasnovas Committed by David S. Miller Nov 24, 2015

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:

  74e98eb0 ("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>

parent 20f79566

net/rds/connection.c

+0 −6

Original line number	Diff line number	Diff line
		@@ -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);

net/rds/send.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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;