191f59dc17
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>