vnc: Fix stack corruption and other bitmap related bugs

Commit bc2429b9174ac2d3c56b7fd35884b0d89ec7fb02 introduced
a severe bug (stack corruption).

bitmap_clear was called with a wrong argument
which caused out-of-bound writes to the local variable 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!

Instead of fixing the wrong parameter value, bitmap_clear(), bitmap_set
and width_mask were removed, and bitmap_intersect() was replaced by
!bitmap_empty(). The new operation is much shorter and equivalent to
the old operations.

The declarations of the dirty bitmaps in vnc.h were also wrong for 64 bit
hosts because of a rounding effect: for these hosts, VNC_MAX_WIDTH is no
longer a multiple of (16 * BITS_PER_LONG), so the rounded value of
VNC_DIRTY_WORDS was too small.

Fix both declarations by using the macro which is designed for this
purpose.

Cc: Corentin Chary <corentincj@iksaif.net>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: Gerhard Wiesinger <lists@wiesinger.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 1 insertions, 5 deletions

diff --git a/ui/vnc.c b/ui/vnc.c
index 610f88485e..34dc0cdc34 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -2383,7 +2383,6 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
     uint8_t *guest_row;
     uint8_t *server_row;
     int cmp_bytes;
-    unsigned long width_mask[VNC_DIRTY_WORDS];
     VncState *vs;
     int has_dirty = 0;
 
@@ -2399,14 +2398,11 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
      * Check and copy modified bits from guest to server surface.
      * Update server dirty map.
      */
-    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);
     cmp_bytes = 16 * ds_get_bytes_per_pixel(vd->ds);
     guest_row  = vd->guest.ds->data;
     server_row = vd->server->data;
     for (y = 0; y < vd->guest.ds->height; y++) {
-        if (bitmap_intersects(vd->guest.dirty[y], width_mask, VNC_DIRTY_WORDS)) {
+        if (!bitmap_empty(vd->guest.dirty[y], VNC_DIRTY_BITS)) {
             int x;
             uint8_t *guest_ptr;
             uint8_t *server_ptr;