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From 74eb4b3e1fcc6d36de0116c2fbbaa308191a1ab7 Mon Sep 17 00:00:00 2001
From: "Daniel P. Berrange" <>
Date: Thu, 8 Feb 2018 17:50:15 +0100
Subject: [PATCH 01/27] vnc: Fix qemu crashed when vnc client disconnect

RH-Author: Daniel P. Berrange <>
Message-id: <>
Patchwork-id: 78947
O-Subject: [RHEL-7.5 qemu-kvm PATCH v1 01/27] vnc: Fix qemu crashed when vnc client disconnect suddenly
Bugzilla: 1527405
RH-Acked-by: Laszlo Ersek <>
RH-Acked-by: Gerd Hoffmann <>
RH-Acked-by: Miroslav Rezanina <>

From: "Gonglei (Arei)" <>


When I use RealVNC viewer client ( to connect vnc server,
the client disconnect suddenly, and I click reconnect button immediately, then the Qemu crashed.

In the function vnc_worker_thread_loop, will call vnc_async_encoding_start
to set the local vs->output buffer by global queue's buffer. Then send rectangles to
the vnc client call function vnc_send_framebuffer_update. Finally, Under normal circumstances,
call vnc_async_encoding_end to set the global queue'buffer by the local vs->output conversely.

When the vnc client disconnect, the job->vs->csock will be set to -1. And the current prcoess
logic will goto disconnected partion without call function vnc_async_encoding_end.
But, the function vnc_send_framebuffer_update will call buffer_reserve, which
maybe call g_realloc reset the local vs's buffer, meaning the global queue's buffer is modified also.
If anyone use the original global queue's buffer memory will cause corruption and then crash qemu.

This patch assure the function vnc_async_encoding_end being called
even though the vnc client disconnect suddenly.

Signed-off-by: Gonglei <>
Signed-off-by: Gerd Hoffmann <>
(cherry picked from commit e3c1adf16e38714ebd761dd02517dd07760ba6d2)
Signed-off-by: Miroslav Rezanina <>
 ui/vnc-jobs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/ui/vnc-jobs.c b/ui/vnc-jobs.c
index 2d3fce8..a141f40 100644
--- a/ui/vnc-jobs.c
+++ b/ui/vnc-jobs.c
@@ -252,6 +252,8 @@ static int vnc_worker_thread_loop(VncJobQueue *queue)
         if (job->vs->csock == -1) {
+            /* Copy persistent encoding data */
+            vnc_async_encoding_end(job->vs, &vs);
             goto disconnected;
@@ -278,6 +280,9 @@ static int vnc_worker_thread_loop(VncJobQueue *queue)
         vnc_async_encoding_end(job->vs, &vs);
+    }  else {
+        /* Copy persistent encoding data */
+        vnc_async_encoding_end(job->vs, &vs);