[Qemu-devel] [PATCH] vnc: Fix heap corruption

[Stefan Weil]

Commit bc2429b9174ac2d3c56b7fd35884b0d89ec7fb02 introduced
a severe bug (heap corruption).

bitmap_clear was called with a wrong argument
which caused out-of-bound writes to width_mask.

This bug was detected with QEMU running on windows.
It also occurs with wine:

*** stack smashing detected ***:  terminated
wine: Unhandled illegal instruction at address 0x6115c7 (thread 0009), starting 
debugger...

The bug is not windows specific!

Cc: Corentin Chary <address@hidden>
Cc: Anthony Liguori <address@hidden>
Signed-off-by: Stefan Weil <address@hidden>
---
 ui/vnc.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/ui/vnc.c b/ui/vnc.c
index af55156..89f71da 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -2401,7 +2401,7 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
      */
     bitmap_set(width_mask, 0, (ds_get_width(vd->ds) / 16));
     bitmap_clear(width_mask, (ds_get_width(vd->ds) / 16),
-                 VNC_DIRTY_WORDS * BITS_PER_LONG);
+                 (VNC_MAX_WIDTH - ds_get_width(vd->ds)) / 16);
     cmp_bytes = 16 * ds_get_bytes_per_pixel(vd->ds);
     guest_row  = vd->guest.ds->data;
     server_row = vd->server->data;
-- 
1.7.2.3