From 5c99bd7a9de1f1a64d948776482ae7103091fac2 Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Fri, 26 Jan 2018 07:30:05 +0100 Subject: [PATCH 2/4] vga: check the validation of memory addr when draw text RH-Author: Gerd Hoffmann Message-id: <20180126073005.15344-2-kraxel@redhat.com> Patchwork-id: 78710 O-Subject: [RHEL-7.5 qemu-kvm PATCH 1/1] vga: check the validation of memory addr when draw text Bugzilla: 1534691 RH-Acked-by: Dr. David Alan Gilbert RH-Acked-by: Laszlo Ersek RH-Acked-by: Miroslav Rezanina From: linzhecheng 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 (cherry picked from commit 191f59dc17396bb5a8da50f8c59b6e0a430711a4) Signed-off-by: Miroslav Rezanina --- hw/display/vga.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/hw/display/vga.c b/hw/display/vga.c index c40744f..017e951 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -1328,6 +1328,9 @@ 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) -- 1.8.3.1