pcnet: force the buffer access to be in bounds during tx

4096 is the maximum length per TMD and it is also currently the size of
the relay buffer pcnet driver uses for sending the packet data to QEMU
for further processing. With packet spanning multiple TMDs it can
happen that the overall packet size will be bigger than sizeof(buffer),
which results in memory corruption.

Fix this by only allowing to queue maximum sizeof(buffer) bytes.

This is CVE-2015-3209.

Signed-off-by: Petr Matousek <pmatouse@redhat.com>
Reported-by: Matt Tait <matttait@google.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/hw/net/pcnet.c b/hw/net/pcnet.c
index 667a327c0220272e6458c48fd21da455fcf80776..fdea333e60c22cce3536e7acbaba25570a6fd152 100644 (file)
--- a/hw/net/pcnet.c
+++ b/hw/net/pcnet.c
@@ -1254,6 +1254,14 @@ 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)) {
+            s->xmit_pos = -1;
+            goto txdone;
+        }
+
         s->phys_mem_read(s->dma_opaque, PHYSADDR(s, tmd.tbadr),
                          s->buffer + s->xmit_pos, bcnt, CSR_BSWP(s));
         s->xmit_pos += bcnt;