[Qemu-stable] [PULL 1/3] e1000: Avoid infinite loop in processing transmit descriptor (CVE-2015-6815)

[Stefan Hajnoczi]

From: P J P <address@hidden>

While processing transmit descriptors, it could lead to an infinite
loop if 'bytes' was to become zero; Add a check to avoid it.

[The guest can force 'bytes' to 0 by setting the hdr_len and mss
descriptor fields to 0.
--Stefan]

Signed-off-by: P J P <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Thomas Huth <address@hidden>
Message-id: address@hidden
---
 hw/net/e1000.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/net/e1000.c b/hw/net/e1000.c
index 5c6bcd0..09c9e9d 100644
--- a/hw/net/e1000.c
+++ b/hw/net/e1000.c
@@ -740,7 +740,8 @@ process_tx_desc(E1000State *s, struct e1000_tx_desc *dp)
                 memmove(tp->data, tp->header, tp->hdr_len);
                 tp->size = tp->hdr_len;
             }
-        } while (split_size -= bytes);
+            split_size -= bytes;
+        } while (bytes && split_size);
     } else if (!tp->tse && tp->cptse) {
         // context descriptor TSE is not set, while data descriptor TSE is set
         DBGOUT(TXERR, "TCP segmentation error\n");
-- 
2.4.3