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 8cc6cb66da5e5b666402207cb0af06f95efc8971..f77e00f5a072d0ad203eec31fe09cea34d2e4e29 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;