From ad0343a9c903b79c6dd3ecdafb05a704c14514b9 Mon Sep 17 00:00:00 2001
From: Hans de Goede <hdegoede@redhat.com>
Date: Fri, 5 Apr 2013 11:30:24 +0200
Subject: [PATCH] spice-qemu-char: vmc_write: Don't write more bytes then we're
 asked too

This one took me eons to debug, but I've finally found it now, oh well.

The usage of the MIN macro in this line:
    last_out = MIN(len, qemu_chr_be_can_write(scd->chr));

Causes qemu_chr_be_can_write to be called *twice*, since the MIN macro
evaluates its arguments twice (bad MIN macro, bad!). And the result of
the call can change between the 2 calls since the guest may have consumed
some data from the virtio ringbuffer between the calls!

When this happens it is possible for qemu_chr_be_can_write to return less
then len in the call made for the comparision, and then to return more then
len in the actual call for the return-value of MIN, after which we will end
up writing len data + some extra garbage, not good.

This patch fixes this by only calling qemu_chr_be_can_write once.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 75c439bc65c07d76f5e74c734ed5432bc6114a3b)
---
 spice-qemu-char.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/spice-qemu-char.c b/spice-qemu-char.c
index 5065240..82f3f77 100644
--- a/spice-qemu-char.c
+++ b/spice-qemu-char.c
@@ -41,7 +41,8 @@ static int vmc_write(SpiceCharDeviceInstance *sin, const uint8_t *buf, int len)
     uint8_t* p = (uint8_t*)buf;
 
     while (len > 0) {
-        last_out = MIN(len, qemu_chr_be_can_write(scd->chr));
+        int can_write = qemu_chr_be_can_write(scd->chr);
+        last_out = MIN(len, can_write);
         if (last_out <= 0) {
             break;
         }