From dc546cbfdefb8ddbaf121d3b075ca723df264d1c Mon Sep 17 00:00:00 2001
From: Vlad Yasevich <vyasevic@redhat.com>
Date: Wed, 16 Dec 2015 02:58:22 +0100
Subject: [PATCH 5/6] rtl8139: Fix receive buffer overflow check

Message-id: <1450234703-7606-2-git-send-email-vyasevic@redhat.com>
Patchwork-id: 68617
O-Subject: [RHEL7.3 qemu-kvm PATCH 1/2] rtl8139: Fix receive buffer overflow check
Bugzilla: 1252757
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
RH-Acked-by: Xiao Wang <jasowang@redhat.com>

rtl8139_do_receive() tries to check for the overflow condition
by making sure that packet_size + 8 does not exceed the
available buffer space.  The issue here is that RxBuffAddr,
used to calculate available buffer space, is aligned to a
a 4 byte boundry after every update.  So it is possible that
every packet ends up being slightly padded when written
to the receive buffer.  This padding is not taken into
account when checking for overflow and we may end up missing
the overflow condition can causing buffer overwrite.

This patch takes alignment into consideration when
checking for overflow condition.

Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Message-id: 1441121206-6997-2-git-send-email-vyasevic@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit fabdcd3392f16fc666b1d04fc1bbe5f1dbbf10a4)
Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/net/rtl8139.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c
index 4f89328..6a167df 100644
--- a/hw/net/rtl8139.c
+++ b/hw/net/rtl8139.c
@@ -1137,7 +1137,9 @@ static ssize_t rtl8139_do_receive(NetClientState *nc, const uint8_t *buf, size_t
 
         /* if receiver buffer is empty then avail == 0 */
 
-        if (avail != 0 && size + 8 >= avail)
+#define RX_ALIGN(x) (((x) + 3) & ~0x3)
+
+        if (avail != 0 && RX_ALIGN(size + 8) >= avail)
         {
             DPRINTF("rx overflow: rx buffer length %d head 0x%04x "
                 "read 0x%04x === available 0x%04x need 0x%04x\n",
@@ -1165,7 +1167,7 @@ static ssize_t rtl8139_do_receive(NetClientState *nc, const uint8_t *buf, size_t
         rtl8139_write_buffer(s, (uint8_t *)&val, 4);
 
         /* correct buffer write pointer */
-        s->RxBufAddr = MOD2((s->RxBufAddr + 3) & ~0x3, s->RxBufferSize);
+        s->RxBufAddr = MOD2(RX_ALIGN(s->RxBufAddr), s->RxBufferSize);
 
         /* now we can signal we have received something */
 
-- 
1.8.3.1