On Mon, Oct 25, 2021 at 02:01:30PM -0500, George Kennedy wrote:
Do a sanity check on pixclock value before using it as a divisor.
Syzkaller reported a divide error in cirrusfb_check_pixclock.
divide error: 0000 [#1] SMP KASAN PTI CPU: 0 PID: 14938 Comm: cirrusfb_test Not tainted 5.15.0-rc6 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2 RIP: 0010:cirrusfb_check_var+0x6f1/0x1260
Call Trace: fb_set_var+0x398/0xf90 do_fb_ioctl+0x4b8/0x6f0 fb_ioctl+0xeb/0x130 __x64_sys_ioctl+0x19d/0x220 do_syscall_64+0x3a/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae
Signed-off-by: George Kennedy george.kennedy@oracle.com
drivers/video/fbdev/cirrusfb.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c index 93802ab..099ddcb 100644 --- a/drivers/video/fbdev/cirrusfb.c +++ b/drivers/video/fbdev/cirrusfb.c @@ -477,6 +477,9 @@ static int cirrusfb_check_pixclock(const struct fb_var_screeninfo *var, struct cirrusfb_info *cinfo = info->par; unsigned maxclockidx = var->bits_per_pixel >> 3;
- if (!var->pixclock)
return -EINVAL;
Shouldn't you be checking further up the call chain where this got set to 0?
What logic allows this to be a valid value? What about all other fb drivers?
thanks,
greg k-h