e1000: Avoid infinite loop in processing transmit descriptor (CVE-2015-6815)

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 <[email protected]>
Signed-off-by: Stefan Hajnoczi <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Message-id: 1441383666[email protected]

diff --git a/hw/net/e1000.c b/hw/net/e1000.c
index 5c6bcd001491f6a50ebe09394e66b37026af5fc3..09c9e9d53b0bf534225b22728f8e835e72520f0d 100644 (file)
--- 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");