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>

diff --git a/slirp/udp.c b/slirp/udp.c
index 9286cb7d3137000268ecc58b8792b63482aa8559..e748b444be2b454accb2f108e49f9652cb8be69d 100644 (file)
--- 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;