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From ad0343a9c903b79c6dd3ecdafb05a704c14514b9 Mon Sep 17 00:00:00 2001
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From: Hans de Goede <hdegoede@redhat.com>
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Date: Fri, 5 Apr 2013 11:30:24 +0200
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Subject: [PATCH] spice-qemu-char: vmc_write: Don't write more bytes then we're
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asked too
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This one took me eons to debug, but I've finally found it now, oh well.
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The usage of the MIN macro in this line:
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last_out = MIN(len, qemu_chr_be_can_write(scd->chr));
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Causes qemu_chr_be_can_write to be called *twice*, since the MIN macro
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evaluates its arguments twice (bad MIN macro, bad!). And the result of
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the call can change between the 2 calls since the guest may have consumed
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some data from the virtio ringbuffer between the calls!
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When this happens it is possible for qemu_chr_be_can_write to return less
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then len in the call made for the comparision, and then to return more then
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len in the actual call for the return-value of MIN, after which we will end
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up writing len data + some extra garbage, not good.
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This patch fixes this by only calling qemu_chr_be_can_write once.
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Signed-off-by: Hans de Goede <hdegoede@redhat.com>
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Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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(cherry picked from commit 75c439bc65c07d76f5e74c734ed5432bc6114a3b)
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---
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spice-qemu-char.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/spice-qemu-char.c b/spice-qemu-char.c
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index 5065240..82f3f77 100644
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--- a/spice-qemu-char.c
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+++ b/spice-qemu-char.c
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@@ -41,7 +41,8 @@ static int vmc_write(SpiceCharDeviceInstance *sin, const uint8_t *buf, int len)
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uint8_t* p = (uint8_t*)buf;
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while (len > 0) {
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- last_out = MIN(len, qemu_chr_be_can_write(scd->chr));
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+ int can_write = qemu_chr_be_can_write(scd->chr);
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+ last_out = MIN(len, can_write);
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if (last_out <= 0) {
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break;
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}
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