cirrus: fix oob access issue (CVE-2017-2615)

When doing bitblt copy in backward mode, we should minus the
blt width first just like the adding in the forward mode. This
can avoid the oob access of the front of vga's vram.

This is XSA-208.

upstream-commit-id: 62d4c6bd5263bb8413a06c80144fc678df6dfb64

Signed-off-by: Li Qiang <liqiang6-s@360.cn>
{ kraxel: with backward blits (negative pitch) addr is the topmost
          address, so check it as-is against vram size ]

Cc: qemu-stable@nongnu.org
Cc: P J P <ppandit@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wolfgang Bumiller <w.bumiller@proxmox.com>
Fixes: d3532a0db02296e687711b8cdc7791924efccea0 (CVE-2014-8106)
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1485938101-26602-1-git-send-email-kraxel@redhat.com
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>

diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
index 27252646bc7817aa8b79c4fd2042769f6627b7cc..8f86142b46e9fc7b663f8e4c66d917d84edeea86 100644 (file)
--- a/hw/display/cirrus_vga.c
+++ b/hw/display/cirrus_vga.c
@@ -270,10 +270,9 @@ static bool blit_region_is_unsafe(struct CirrusVGAState *s,
 {
     if (pitch < 0) {
         int64_t min = addr
-            + ((int64_t)s->cirrus_blt_height-1) * pitch;
-        int32_t max = addr
-            + s->cirrus_blt_width;
-        if (min < 0 || max >= s->vga.vram_size) {
+            + ((int64_t)s->cirrus_blt_height - 1) * pitch
+            - s->cirrus_blt_width;
+        if (min < -1 || addr >= s->vga.vram_size) {
             return true;
         }
     } else {