From 191f59dc17396bb5a8da50f8c59b6e0a430711a4 Mon Sep 17 00:00:00 2001 From: linzhecheng Date: Thu, 11 Jan 2018 21:27:24 +0800 Subject: 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 Message-id: 20180111132724.13744-1-linzhecheng@huawei.com Fixes: CVE-2018-5683 Signed-off-by: Gerd Hoffmann --- hw/display/vga.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'hw') diff --git a/hw/display/vga.c b/hw/display/vga.c index a041200..6e78a4e 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -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) -- cgit v1.1