vmsvga: add more fifo checks

Make sure all fifo ptrs are within range.

Fixes: CVE-2016-4454
Cc: qemu-stable@nongnu.org
Cc: P J P <ppandit@redhat.com>
Reported-by: 李强 <liqiang6-s@360.cn>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1464592161-18348-3-git-send-email-kraxel@redhat.com
(cherry picked from commit c2e3c54)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/display/vmware_vga.c

@@ -563,7 +563,10 @@ static inline int vmsvga_fifo_length(struct vmsvga_state_s *s)
     if (CMD(min) < (uint8_t *) s->cmd->fifo - (uint8_t *) s->fifo) {
         return 0;
     }
-    if (CMD(max) > SVGA_FIFO_SIZE) {
+    if (CMD(max) > SVGA_FIFO_SIZE ||
+        CMD(min) >= SVGA_FIFO_SIZE ||
+        CMD(stop) >= SVGA_FIFO_SIZE ||
+        CMD(next_cmd) >= SVGA_FIFO_SIZE) {
         return 0;
     }
     if (CMD(max) < CMD(min) + 10 * 1024) {