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 ]

[ This is CVE-2017-2615 / XSA-208  - Ian Jackson ]

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>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
(cherry picked from commit c4018bc4d638918b3f8fb49dd3b379abb5658ee1)
(cherry picked from commit a1d57bb66d5f7e3a86e47c01431c823e217b23ab)
(cherry picked from commit a20cf3a6edd051f2f2eb734a7bcda6c6246740ff)
(cherry picked from commit d0360192b805d13353b0bb100fe0cf927a2861e7)
(cherry picked from commit 6a207f06f62a58e5d56f463722bb23135cd1cc20)

diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
index 00736d2104a44fc1fafd4bf4870fb71572f5cfb2..1b5106c871315c176f84a08914febc3a3ba2b0cb 100644 (file)
--- a/hw/cirrus_vga.c
+++ b/hw/cirrus_vga.c
@@ -308,10 +308,9 @@ 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->vram_size) {
+            + ((int64_t)s->cirrus_blt_height - 1) * pitch
+            - s->cirrus_blt_width;
+        if (min < -1 || addr >= s->vram_size) {
             return true;
         }
     } else {