fix :cirrus_vga fix OOB read case qemu Segmentation fault

check the validity of parameters in cirrus_bitblt_rop_fwd_transp_xxx
and cirrus_bitblt_rop_fwd_xxx to avoid the OOB read which causes qemu Segmentation fault.

After the fix, we will touch the assert in
cirrus_invalidate_region:
assert(off_cur_end >= off_cur);
Signed-off-by: Nfangying <fangying1@huawei.com>
Signed-off-by: Nhangaohuai <hangaohuai@huawei.com>
Message-id: 20170314063919.16200-1-hangaohuai@huawei.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 215902d7)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

hw/display/cirrus_vga_rop.h

@@ -97,6 +97,11 @@ glue(glue(cirrus_bitblt_rop_fwd_transp_, ROP_NAME),_8)(CirrusVGAState *s,
     uint8_t p;
     dstpitch -= bltwidth;
     srcpitch -= bltwidth;
+
+    if (bltheight > 1 && (dstpitch < 0 || srcpitch < 0)) {
+        return;
+    }
+
     for (y = 0; y < bltheight; y++) {
         for (x = 0; x < bltwidth; x++) {
 	    p = *dst;
@@ -143,6 +148,11 @@ glue(glue(cirrus_bitblt_rop_fwd_transp_, ROP_NAME),_16)(CirrusVGAState *s,
     uint8_t p1, p2;
     dstpitch -= bltwidth;
     srcpitch -= bltwidth;
+
+    if (bltheight > 1 && (dstpitch < 0 || srcpitch < 0)) {
+        return;
+    }
+
     for (y = 0; y < bltheight; y++) {
         for (x = 0; x < bltwidth; x+=2) {
 	    p1 = *dst;