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vga: fix region calculation 

Typically the scanline length and the line offset are identical.  But
in case they are not our calculation for region_end is incorrect.  Using
line_offset is fine for all scanlines, except the last one where we have
to use the actual scanline length.

Fixes: CVE-2018-7550
Reported-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Prasad J Pandit <pjp@fedoraproject.org>
Tested-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Message-id: 20180309143704.13420-1-kraxel@redhat.com
This commit is contained in:
Gerd Hoffmann 2018-03-09 15:37:04 +01:00
parent e4ae62b802
commit 7cdc61becd
1 changed files with 2 additions and 0 deletions
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2
hw/display/vga.c
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@ -1483,6 +1483,8 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
region_start = (s->start_addr * 4);
region_end = region_start + (ram_addr_t)s->line_offset * height;
region_end += width * s->get_bpp(s) / 8; /* scanline length */
region_end -= s->line_offset;
if (region_end > s->vbe_size) {
/* wraps around (can happen with cirrus vbe modes) */
region_start = 0;