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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7EE7C54EE9 for ; Fri, 2 Sep 2022 12:28:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235494AbiIBM2D (ORCPT ); Fri, 2 Sep 2022 08:28:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235829AbiIBM1d (ORCPT ); Fri, 2 Sep 2022 08:27:33 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5539DD743; Fri, 2 Sep 2022 05:24:09 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 5CE8AB82A91; Fri, 2 Sep 2022 12:23:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8B22EC433D7; Fri, 2 Sep 2022 12:23:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1662121397; bh=X2kyHRGmPFA4IG7DMX7lJ498RS9kJ6XcbHqpncdeLrk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZQ9kEfMu7pUEKUbPr2XJr+iLy9uJHs9jsMiC5kbi3ZLTuTYgZz40jnfhWDZxsEXai LlIwKpcPz5EfF7CEX9lOcJBQvqKh+x1Vp1AAr9zhamQBbDmCCtEZ4t30FOAAnFJkQn ATDFMOGwO2DB02SYN8ibchlMMSHMxHvfx5eXqNpU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Zheyu Ma , Letu Ren , Helge Deller Subject: [PATCH 4.14 35/42] fbdev: fb_pm2fb: Avoid potential divide by zero error Date: Fri, 2 Sep 2022 14:18:59 +0200 Message-Id: <20220902121359.998704160@linuxfoundation.org> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20220902121358.773776406@linuxfoundation.org> References: <20220902121358.773776406@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Letu Ren commit 19f953e7435644b81332dd632ba1b2d80b1e37af upstream. In `do_fb_ioctl()` of fbmem.c, if cmd is FBIOPUT_VSCREENINFO, var will be copied from user, then go through `fb_set_var()` and `info->fbops->fb_check_var()` which could may be `pm2fb_check_var()`. Along the path, `var->pixclock` won't be modified. This function checks whether reciprocal of `var->pixclock` is too high. If `var->pixclock` is zero, there will be a divide by zero error. So, it is necessary to check whether denominator is zero to avoid crash. As this bug is found by Syzkaller, logs are listed below. divide error in pm2fb_check_var Call Trace: fb_set_var+0x367/0xeb0 drivers/video/fbdev/core/fbmem.c:1015 do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1110 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1189 Reported-by: Zheyu Ma Signed-off-by: Letu Ren Signed-off-by: Helge Deller Signed-off-by: Greg Kroah-Hartman --- drivers/video/fbdev/pm2fb.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/drivers/video/fbdev/pm2fb.c +++ b/drivers/video/fbdev/pm2fb.c @@ -614,6 +614,11 @@ static int pm2fb_check_var(struct fb_var return -EINVAL; } + if (!var->pixclock) { + DPRINTK("pixclock is zero\n"); + return -EINVAL; + } + if (PICOS2KHZ(var->pixclock) > PM2_MAX_PIXCLOCK) { DPRINTK("pixclock too high (%ldKHz)\n", PICOS2KHZ(var->pixclock));