[Qemu-devel] [PATCH for-2.0] virtio-net: fix guest-triggerable buffer overrun

["Michael S. Tsirkin" <mst@redhat.com>]

When VM guest programs multicast addresses for
a virtio net card, it supplies a 32 bit
entries counter for the number of addresses.
These addresses are read into tail portion of
a fixed macs array which has size MAC_TABLE_ENTRIES,
at offset equal to in_use.

To avoid overflow of this array by guest, qemu attempts
to test the size as follows:
-    if (in_use + mac_data.entries <= MAC_TABLE_ENTRIES) {

however, as mac_data.entries is uint32_t, this sum
can overflow, e.g. if in_use is 1 and mac_data.entries
is 0xffffffff then in_use + mac_data.entries will be 0.

Qemu will then read guest supplied buffer into this
memory, overflowing buffer on heap.

CVE-2014-0150

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Passed basic tests.
CVE fix so pick this up for -rc3?

 hw/net/virtio-net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 439477b..33bd233 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -677,7 +677,7 @@ static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,
         goto error;
     }
 
-    if (in_use + mac_data.entries <= MAC_TABLE_ENTRIES) {
+    if (mac_data.entries <= MAC_TABLE_ENTRIES - in_use) {
         s = iov_to_buf(iov, iov_cnt, 0, &macs[in_use * ETH_ALEN],
                        mac_data.entries * ETH_ALEN);
         if (s != mac_data.entries * ETH_ALEN) {
-- 
MST