From: Prasad J Pandit <pjp@fedoraproject.org>

Date: Fri, 20 Nov 2015 11:50:31 +0530

Subject: [PATCH] net: pcnet: add check to validate receive data

 size(CVE-2015-7504)

In loopback mode, pcnet_receive routine appends CRC code to the

receive buffer. If the data size given is same as the buffer size,

the appended CRC code overwrites 4 bytes after s->buffer. Added a

check to avoid that.

Reported by: Qinghao Tang <luodalongde@gmail.com>

Cc: qemu-stable@nongnu.org

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>

Signed-off-by: Jason Wang <jasowang@redhat.com>

(cherry picked from commit 837f21aacf5a714c23ddaadbbc5212f9b661e3f7)

---

 hw/net/pcnet.c | 8 +++++---

 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/hw/net/pcnet.c b/hw/net/pcnet.c

index 68b9981..03a56b2 100644

--- a/hw/net/pcnet.c

+++ b/hw/net/pcnet.c

@@ -1094,7 +1094,7 @@ ssize_t pcnet_receive(NetClientState *nc, const uint8_t *buf, size_t size_)

                 uint32_t fcs = ~0;

                 uint8_t *p = src;

-                while (p != &src[size-4])

+                while (p != &src[size])

                     CRC(fcs, *p++);

                 crc_err = (*(uint32_t *)p != htonl(fcs));

             }

@@ -1243,8 +1243,10 @@ static void pcnet_transmit(PCNetState *s)

         bcnt = 4096 - GET_FIELD(tmd.length, TMDL, BCNT);

         /* if multi-tmd packet outsizes s->buffer then skip it silently.

-           Note: this is not what real hw does */

-        if (s->xmit_pos + bcnt > sizeof(s->buffer)) {

+         * Note: this is not what real hw does.

+         * Last four bytes of s->buffer are used to store CRC FCS code.

+         */

+        if (s->xmit_pos + bcnt > sizeof(s->buffer) - 4) {

             s->xmit_pos = -1;

             goto txdone;

         }