[Xen-changelog] [qemu-xen stable-4.4] net: pcnet: add check to validate receive data size(CVE-2015-7504)

[patchbot@xxxxxxx]

commit 11ac1da95c4e8b2c9c627e0cbcaa50c90c298a1b
Author:     Prasad J Pandit <pjp@xxxxxxxxxxxxxxxxx>
AuthorDate: Fri Nov 20 11:50:31 2015 +0530
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
CommitDate: Fri Feb 5 14:53:54 2016 +0000

    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@xxxxxxxxx>
    Cc: qemu-stable@xxxxxxxxxx
    Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: Prasad J Pandit <pjp@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 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 af691dd..34098e5 100644
--- a/hw/net/pcnet.c
+++ b/hw/net/pcnet.c
@@ -1113,7 +1113,7 @@ 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));
             }
@@ -1262,8 +1262,10 @@ 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;
         }
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.4

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