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@xxxxxxxxxx> > --- > 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
