slirp: udp: fix NULL pointer dereference because of uninitialized socket

When guest sends udp packet with source port and source addr 0,
uninitialized socket is picked up when looking for matching and already
created udp sockets, and later passed to sosendto() where NULL pointer
dereference is hit during so->slirp->vnetwork_mask.s_addr access.

Fix this by checking that the socket is not just a socket stub.

This is CVE-2014-3640.

Signed-off-by: Petr Matousek <pmatouse@redhat.com>
Reported-by: Xavier Mehrenberger <xavier.mehrenberger@airbus.com>
Reported-by: Stephane Duverger <stephane.duverger@eads.net>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Message-id: 20140918063537.GX9321@dhcp-25-225.brq.redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/slirp/udp.c b/slirp/udp.c
index 8cc6cb66da..f77e00f5a0 100644
--- a/slirp/udp.c
+++ b/slirp/udp.c
@@ -152,7 +152,7 @@ udp_input(register struct mbuf *m, int iphlen)
 	 * Locate pcb for datagram.
 	 */
 	so = slirp->udp_last_so;
-	if (so->so_lport != uh->uh_sport ||
+	if (so == &slirp->udb || so->so_lport != uh->uh_sport ||
 	    so->so_laddr.s_addr != ip->ip_src.s_addr) {
 		struct socket *tmp;