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 178E3ECAAA1 for ; Tue, 30 Aug 2022 17:32:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231986AbiH3RcK (ORCPT ); Tue, 30 Aug 2022 13:32:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56660 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231787AbiH3Rbk (ORCPT ); Tue, 30 Aug 2022 13:31:40 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A16542AC4D; Tue, 30 Aug 2022 10:28:23 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 79362617C1; Tue, 30 Aug 2022 17:26:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E868DC433C1; Tue, 30 Aug 2022 17:26:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1661880418; bh=whvkUYJpp+OMkxLwPyh6AxZcY193wuz/Z41ppsLlUro=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=b6nLol4WFFGCCJZfC6MOvBLmuG168aw1V4B5RgoEqvkk9eSgyotEOjHd9xc44UHgD NgvQNxAUv0Dnfh+WCxFLTa1xa23iOz+R3gPN7rhDjlzp+TdAVD+NeIjvFLmhGrKIcp wtwdQBpRcYqXw826VXF+rYmwESpoYtlPlPI7M7oChzxISBM6V8dB1u9l5Byxjuy6+n 9dMBq4AjG/OAXr2rsllBYofoNVioBkCM6qBDAMgfkLK03I/rIvY+avQh0DGxeOJEBW Qcusi5bvMvXd42fVdpRaVwtRXk9VqqJs7zGTFmBR30n+5zvRlFTeJJej1NuCkFN6QU wwbK6vTH7qVVQ== 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 4.14 7/8] fbdev: fb_pm2fb: Avoid potential divide by zero error Date: Tue, 30 Aug 2022 13:26:30 -0400 Message-Id: <20220830172631.581969-7-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220830172631.581969-1-sashal@kernel.org> References: <20220830172631.581969-1-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-fbdev@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 bd6c2f5f6095d..a5375b09415a6 100644 --- a/drivers/video/fbdev/pm2fb.c +++ b/drivers/video/fbdev/pm2fb.c @@ -614,6 +614,11 @@ 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