Hi George, On Mon, Oct 25, 2021 at 03:33:43PM -0400, George Kennedy wrote: > > > On 10/25/2021 3:07 PM, Greg KH wrote: > > 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? > I recall we had a similar discussion when Zheyu Ma <zheyuma97@xxxxxxxxx> added the same checks to at least 3 fbdev drivers. The conclusion was that the check belongs in the individual check functions - IIRC. Maybe Zheyu or google can help find the original thread. Sam
