Move dst calculation into the loop, so we apply the mask on each
interation and will not overflow vga memory.

Cc: Prasad J Pandit <pjp@fedoraproject.org>
Reported-by: Niu Guoxiang <niuguoxiang@huawei.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/display/cirrus_vga.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
index afc290ab91..cf096df90f 100644
--- a/hw/display/cirrus_vga.c
+++ b/hw/display/cirrus_vga.c
@@ -2038,15 +2038,14 @@ static void cirrus_mem_writeb_mode4and5_8bpp(CirrusVGAState * s,
     unsigned val = mem_value;
     uint8_t *dst;
 
-    dst = s->vga.vram_ptr + (offset &= s->cirrus_addr_mask);
     for (x = 0; x < 8; x++) {
+	dst = s->vga.vram_ptr + ((offset+x) & s->cirrus_addr_mask);
 	if (val & 0x80) {
 	    *dst = s->cirrus_shadow_gr1;
 	} else if (mode == 5) {
 	    *dst = s->cirrus_shadow_gr0;
 	}
 	val <<= 1;
-	dst++;
     }
     memory_region_set_dirty(&s->vga.vram, offset, 8);
 }
@@ -2060,8 +2059,8 @@ static void cirrus_mem_writeb_mode4and5_16bpp(CirrusVGAState * s,
     unsigned val = mem_value;
     uint8_t *dst;
 
-    dst = s->vga.vram_ptr + (offset &= s->cirrus_addr_mask);
     for (x = 0; x < 8; x++) {
+	dst = s->vga.vram_ptr + ((offset + 2 * x) & s->cirrus_addr_mask & ~1);
 	if (val & 0x80) {
 	    *dst = s->cirrus_shadow_gr1;
 	    *(dst + 1) = s->vga.gr[0x11];
@@ -2070,7 +2069,6 @@ static void cirrus_mem_writeb_mode4and5_16bpp(CirrusVGAState * s,
 	    *(dst + 1) = s->vga.gr[0x10];
 	}
 	val <<= 1;
-	dst += 2;
     }
     memory_region_set_dirty(&s->vga.vram, offset, 16);
 }
-- 
2.9.3

Hi,

This series seems to have some coding style problems. See output below for
more information:

Type: series
Message-id: 20171011071423.20179-1-kraxel@redhat.com
Subject: [Qemu-devel] [PATCH] cirrus: fix oob access in mode4and5 write functions

=== TEST SCRIPT BEGIN ===
#!/bin/bash

BASE=base
n=1
total=$(git log --oneline $BASE.. | wc -l)
failed=0

git config --local diff.renamelimit 0
git config --local diff.renames True

commits="$(git log --format=%H --reverse $BASE..)"
for c in $commits; do
    echo "Checking PATCH $n/$total: $(git log -n 1 --format=%s $c)..."
    if ! git show $c --format=email | ./scripts/checkpatch.pl --mailback -; then
        failed=1
        echo
    fi
    n=$((n+1))
done

exit $failed
=== TEST SCRIPT END ===

Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384
From https://github.com/patchew-project/qemu
 t [tag update]            patchew/20171011000649.22012-1-david@gibson.dropbear.id.au -> patchew/20171011000649.22012-1-david@gibson.dropbear.id.au
Switched to a new branch 'test'
cb458ab691 cirrus: fix oob access in mode4and5 write functions

=== OUTPUT BEGIN ===
Checking PATCH 1/1: cirrus: fix oob access in mode4and5 write functions...
ERROR: code indent should never use tabs
#24: FILE: hw/display/cirrus_vga.c:2042:
+^Idst = s->vga.vram_ptr + ((offset+x) & s->cirrus_addr_mask);$

ERROR: spaces required around that '+' (ctx:VxV)
#24: FILE: hw/display/cirrus_vga.c:2042:
+	dst = s->vga.vram_ptr + ((offset+x) & s->cirrus_addr_mask);
 	                                ^

ERROR: code indent should never use tabs
#41: FILE: hw/display/cirrus_vga.c:2063:
+^Idst = s->vga.vram_ptr + ((offset + 2 * x) & s->cirrus_addr_mask & ~1);$

total: 3 errors, 0 warnings, 32 lines checked

Your patch has style problems, please review.  If any of these errors
are false positives report them to the maintainer, see
CHECKPATCH in MAINTAINERS.

=== OUTPUT END ===

Test command exited with code: 1


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