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vga: check the validation of memory addr when draw text 

Start a vm with qemu-kvm -enable-kvm -vnc :66 -smp 1 -m 1024 -hda
redhat_5.11.qcow2  -device pcnet -vga cirrus,
then use VNC client to connect to VM, and excute the code below in guest
OS will lead to qemu crash:

int main()
 {
    iopl(3);
    srand(time(NULL));
    int a,b;
    while(1){
	a = rand()%0x100;
	b = 0x3c0 + (rand()%0x20);
        outb(a,b);
    }
    return 0;
}

The above code is writing the registers of VGA randomly.
We can write VGA CRT controller registers index 0x0C or 0x0D
(which is the start address register) to modify the
the display memory address of the upper left pixel
or character of the screen. The address may be out of the
range of vga ram. So we should check the validation of memory address
when reading or writing it to avoid segfault.

Signed-off-by: linzhecheng <linzhecheng@huawei.com>
Message-id: 20180111132724.13744-1-linzhecheng@huawei.com
Fixes: CVE-2018-5683
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
linzhecheng 2018-01-11 21:27:24 +08:00 committed by Gerd Hoffmann
parent 834a336eb9
commit 191f59dc17
1 changed files with 3 additions and 0 deletions
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3
hw/display/vga.c
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@ -1279,6 +1279,9 @@ static void vga_draw_text(VGACommonState *s, int full_update)
cx_min = width;
cx_max = -1;
for(cx = 0; cx < width; cx++) {
if (src + sizeof(uint16_t) > s->vram_ptr + s->vram_size) {
break;
}
ch_attr = *(uint16_t *)src;
if (full_update || ch_attr != *ch_attr_ptr || src == cursor_ptr) {
if (cx < cx_min)