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 46CC1ECAAA1 for ; Tue, 30 Aug 2022 17:32:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232048AbiH3Rcp (ORCPT ); Tue, 30 Aug 2022 13:32:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33268 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231936AbiH3Rbq (ORCPT ); Tue, 30 Aug 2022 13:31:46 -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 78E6D12EC74; Tue, 30 Aug 2022 10:28:17 -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 3701FB81D1A; Tue, 30 Aug 2022 17:26:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 084A6C433D6; Tue, 30 Aug 2022 17:26:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1661880378; bh=dKlYcbJg8jJBwPyfgtu+Hl0XHma2r9ZCS4XvcIUHs8Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aPlRpzzf9kS1DuO8k9642AjN5s5vqDVPHLMQI0dp2OcQSvqeUuqYectzA2rPpWs50 dbePTQy5cOiVwTMEXXvtx9ZfU9INlFuyIBopbqE2uWZ1JgGKrXMXoPD9ALJ1e7zifG Bg96I5QLj/aULc4zrP49pY6t+Hc5KC+Q1eEBX1QpL5GQfJVt1PzjrofnVUYOagxgtY yRZlTQO4a9AoZBoFf2J0rs2v/pkmCpwwrTWUz92XUEgw18y5eHiQ2ZGFFJJcAr1ALX 1voZiSC/wOpDrabgIikcRbXm6buw5RkL78K002OnKF33ivgma42ol1yCrMsNs+SqBq MctjdnfZ38KWw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Letu Ren , Zheyu Ma , Helge Deller , Sasha Levin , baihaowen@meizu.com, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: [PATCH AUTOSEL 4.19 08/10] fbdev: fb_pm2fb: Avoid potential divide by zero error Date: Tue, 30 Aug 2022 13:25:39 -0400 Message-Id: <20220830172541.581820-8-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220830172541.581820-1-sashal@kernel.org> References: <20220830172541.581820-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Letu Ren [ Upstream commit 19f953e7435644b81332dd632ba1b2d80b1e37af ] 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: Sasha Levin --- drivers/video/fbdev/pm2fb.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c index 1dcf02e12af4f..8ae010f07d7da 100644 --- a/drivers/video/fbdev/pm2fb.c +++ b/drivers/video/fbdev/pm2fb.c @@ -616,6 +616,11 @@ static int pm2fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info) 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)); -- 2.35.1