From nobody Thu Dec 18 08:37:37 2025 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 E6282C54EE9 for ; Fri, 2 Sep 2022 12:52:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237894AbiIBMwD (ORCPT ); Fri, 2 Sep 2022 08:52:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43576 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236137AbiIBMvR (ORCPT ); Fri, 2 Sep 2022 08:51:17 -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 505F5F826C; Fri, 2 Sep 2022 05:36:58 -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 1178AB82ACD; Fri, 2 Sep 2022 12:35:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B88CC433D6; Fri, 2 Sep 2022 12:35:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1662122106; bh=Uk4hLiPJocqiO6tbAqBSSCacJn6LjD8UNbJhRkRruFM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mgOhocRfLFDENL3l2CU/RcjtHIldn+oyUSnpoff+Tcl+/6cBKNe2UvA2Tn7UNzYSc 6FbyrZ0bKCmRRAP8BFXt/nWGipPAGeF13cKsukp3Fm0DOazOyW0HxZ6F7NINU41MvX E5P47FGnXPlE9o9ctO6uFlfdZbqk+C0aBAK2g3FY= 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 5.19 15/72] fbdev: fb_pm2fb: Avoid potential divide by zero error Date: Fri, 2 Sep 2022 14:18:51 +0200 Message-Id: <20220902121405.285931536@linuxfoundation.org> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20220902121404.772492078@linuxfoundation.org> References: <20220902121404.772492078@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 @@ -617,6 +617,11 @@ static int pm2fb_check_var(struct fb_var return -EINVAL; } =20 + 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));