From: Prasad J Pandit <address@hidden>

While computing IP checksum, 'net_checksum_calculate' reads
payload length from the packet. It could exceed the given 'data'
buffer size. Add a check to avoid it.

Reported-by: Liu Ling <address@hidden>
Signed-off-by: Prasad J Pandit <address@hidden>
---
 net/checksum.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Update as per review:
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-02/msg06121.html

diff --git a/net/checksum.c b/net/checksum.c
index 14c0855..0942437 100644
--- a/tools/qemu-xen-traditional/net-checksum.c
+++ b/tools/qemu-xen-traditional/net-checksum.c
@@ -59,6 +59,11 @@ void net_checksum_calculate(uint8_t *data, int length)
     int hlen, plen, proto, csum_offset;
     uint16_t csum;
 
+    /* Ensure data has complete L2 & L3 headers. */
+    if (length < 14 + 20) {
+        return;
+    }
+
     if ((data[14] & 0xf0) != 0x40)
 	return; /* not IPv4 */
     hlen  = (data[14] & 0x0f) * 4;
@@ -76,8 +81,9 @@ void net_checksum_calculate(uint8_t *data, int length)
 	return;
     }
 
-    if (plen < csum_offset+2)
-	return;
+    if (plen < csum_offset + 2 || 14 + hlen + plen > length) {
+        return;
+    }
 
     data[14+hlen+csum_offset]   = 0;
     data[14+hlen+csum_offset+1] = 0;
-- 
2.5.0