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vga: fix region calculation

PATCH New Gerd Hoffmann 1 participant 1 message Mar 9, 2018

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Gerd Hoffmann

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PATCH v2 1/1 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 <[email protected]>
Signed-off-by Gerd Hoffmann <[email protected]>
Reviewed-by Prasad J Pandit <[email protected]>
Tested-by Ross Lagerwall <[email protected]>
---
 hw/display/vga.c | 2 ++
 1 file changed, 2 insertions(+)
hw/display/vga.c +2 -0
index 28f298b342..72181330b8 100644
@@ -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;
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2.9.3