From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A465C433FE for ; Mon, 25 Oct 2021 19:07:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1E74160F9D for ; Mon, 25 Oct 2021 19:07:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233645AbhJYTJ4 (ORCPT ); Mon, 25 Oct 2021 15:09:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:60814 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230201AbhJYTJw (ORCPT ); Mon, 25 Oct 2021 15:09:52 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C645C60E08; Mon, 25 Oct 2021 19:07:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1635188849; bh=QkD0aIubb77MfLaXkA4RVCyqVSSVXP4CNLjP63IkeVI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DnQBmEObnLjI/kHoynHgptbLC0L02jt4LCdyS243gJXYt4vnvNZH6UY6PEbgoGTVG 5KdBh4stQvZ3HONTL7xdIip44r91p1GA6+gDA1AYLFmGXeeRmAWIckxf8z8xuw2JSi uJO2d46gy/OVFAn9XCzstEo1zMAssIl4zYYHXs58= Date: Mon, 25 Oct 2021 21:07:25 +0200 From: Greg KH To: George Kennedy Cc: tzimmermann@suse.de, sam@ravnborg.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] video: fbdev: cirrusfb: check pixclock to avoid divide by zero Message-ID: References: <1635188490-15082-1-git-send-email-george.kennedy@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1635188490-15082-1-git-send-email-george.kennedy@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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