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 X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 688F3C433FC for ; Mon, 27 Jul 2020 14:26:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 48EDC208E4 for ; Mon, 27 Jul 2020 14:26:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595860015; bh=/YydLRvkoKVz03blHEasLvIRqIOV/wARQ1buAMOoUk4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=BUiwndF6fK0wxr9qJ3bptEH4gJXy34Cqqth4pQwM/ow6b3id52OquXhuMkiXZIjuQ PZeqouB/prraED//Q4517KvSHe3mLAEM+kKs2wZl27SObgLjYdyA4atebYfsPScBrn g/Or7au1eoWg3o5CnAXcnUl10AjRGBsFc/wR+ASg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732616AbgG0O0b (ORCPT ); Mon, 27 Jul 2020 10:26:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:56754 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731829AbgG0O0b (ORCPT ); Mon, 27 Jul 2020 10:26:31 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EBA1F20663; Mon, 27 Jul 2020 14:26:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595859990; bh=/YydLRvkoKVz03blHEasLvIRqIOV/wARQ1buAMOoUk4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XOinYIGH0TxejZFEArTRZc5z1Csk2ekPT3qgsI9JRtGISvMWJdXgeYiU0gm8cmsLP eDTP+3HSn2e67GwQOOMT2em/Nfd/6zVPai1evt4NwkkMFTIfkgPPMxQ2qZF+m5txlA jvILjc/1sebIDSMtE1m9mmZkbzKU/bwRZDnKDHCk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tetsuo Handa , Daniel Vetter , syzbot Subject: [PATCH 5.7 156/179] fbdev: Detect integer underflow at "struct fbcon_ops"->clear_margins. Date: Mon, 27 Jul 2020 16:05:31 +0200 Message-Id: <20200727134940.273282559@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200727134932.659499757@linuxfoundation.org> References: <20200727134932.659499757@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Tetsuo Handa commit 033724d6864245a11f8e04c066002e6ad22b3fd0 upstream. syzbot is reporting general protection fault in bitfill_aligned() [1] caused by integer underflow in bit_clear_margins(). The cause of this problem is when and how do_vc_resize() updates vc->vc_{cols,rows}. If vc_do_resize() fails (e.g. kzalloc() fails) when var.xres or var.yres is going to shrink, vc->vc_{cols,rows} will not be updated. This allows bit_clear_margins() to see info->var.xres < (vc->vc_cols * cw) or info->var.yres < (vc->vc_rows * ch). Unexpectedly large rw or bh will try to overrun the __iomem region and causes general protection fault. Also, vc_resize(vc, 0, 0) does not set vc->vc_{cols,rows} = 0 due to new_cols = (cols ? cols : vc->vc_cols); new_rows = (lines ? lines : vc->vc_rows); exception. Since cols and lines are calculated as cols = FBCON_SWAP(ops->rotate, info->var.xres, info->var.yres); rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres); cols /= vc->vc_font.width; rows /= vc->vc_font.height; vc_resize(vc, cols, rows); in fbcon_modechanged(), var.xres < vc->vc_font.width makes cols = 0 and var.yres < vc->vc_font.height makes rows = 0. This means that const int fd = open("/dev/fb0", O_ACCMODE); struct fb_var_screeninfo var = { }; ioctl(fd, FBIOGET_VSCREENINFO, &var); var.xres = var.yres = 1; ioctl(fd, FBIOPUT_VSCREENINFO, &var); easily reproduces integer underflow bug explained above. Of course, callers of vc_resize() are not handling vc_do_resize() failure is bad. But we can't avoid vc_resize(vc, 0, 0) which returns 0. Therefore, as a band-aid workaround, this patch checks integer underflow in "struct fbcon_ops"->clear_margins call, assuming that vc->vc_cols * vc->vc_font.width and vc->vc_rows * vc->vc_font.heigh do not cause integer overflow. [1] https://syzkaller.appspot.com/bug?id=a565882df74fa76f10d3a6fec4be31098dbb37c6 Reported-and-tested-by: syzbot Signed-off-by: Tetsuo Handa Acked-by: Daniel Vetter Cc: stable Link: https://lore.kernel.org/r/20200715015102.3814-1-penguin-kernel@I-love.SAKURA.ne.jp Signed-off-by: Greg Kroah-Hartman --- drivers/video/fbdev/core/bitblit.c | 4 ++-- drivers/video/fbdev/core/fbcon_ccw.c | 4 ++-- drivers/video/fbdev/core/fbcon_cw.c | 4 ++-- drivers/video/fbdev/core/fbcon_ud.c | 4 ++-- 4 files changed, 8 insertions(+), 8 deletions(-) --- a/drivers/video/fbdev/core/bitblit.c +++ b/drivers/video/fbdev/core/bitblit.c @@ -216,7 +216,7 @@ static void bit_clear_margins(struct vc_ region.color = color; region.rop = ROP_COPY; - if (rw && !bottom_only) { + if ((int) rw > 0 && !bottom_only) { region.dx = info->var.xoffset + rs; region.dy = 0; region.width = rw; @@ -224,7 +224,7 @@ static void bit_clear_margins(struct vc_ info->fbops->fb_fillrect(info, ®ion); } - if (bh) { + if ((int) bh > 0) { region.dx = info->var.xoffset; region.dy = info->var.yoffset + bs; region.width = rs; --- a/drivers/video/fbdev/core/fbcon_ccw.c +++ b/drivers/video/fbdev/core/fbcon_ccw.c @@ -201,7 +201,7 @@ static void ccw_clear_margins(struct vc_ region.color = color; region.rop = ROP_COPY; - if (rw && !bottom_only) { + if ((int) rw > 0 && !bottom_only) { region.dx = 0; region.dy = info->var.yoffset; region.height = rw; @@ -209,7 +209,7 @@ static void ccw_clear_margins(struct vc_ info->fbops->fb_fillrect(info, ®ion); } - if (bh) { + if ((int) bh > 0) { region.dx = info->var.xoffset + bs; region.dy = 0; region.height = info->var.yres_virtual; --- a/drivers/video/fbdev/core/fbcon_cw.c +++ b/drivers/video/fbdev/core/fbcon_cw.c @@ -184,7 +184,7 @@ static void cw_clear_margins(struct vc_d region.color = color; region.rop = ROP_COPY; - if (rw && !bottom_only) { + if ((int) rw > 0 && !bottom_only) { region.dx = 0; region.dy = info->var.yoffset + rs; region.height = rw; @@ -192,7 +192,7 @@ static void cw_clear_margins(struct vc_d info->fbops->fb_fillrect(info, ®ion); } - if (bh) { + if ((int) bh > 0) { region.dx = info->var.xoffset; region.dy = info->var.yoffset; region.height = info->var.yres; --- a/drivers/video/fbdev/core/fbcon_ud.c +++ b/drivers/video/fbdev/core/fbcon_ud.c @@ -231,7 +231,7 @@ static void ud_clear_margins(struct vc_d region.color = color; region.rop = ROP_COPY; - if (rw && !bottom_only) { + if ((int) rw > 0 && !bottom_only) { region.dy = 0; region.dx = info->var.xoffset; region.width = rw; @@ -239,7 +239,7 @@ static void ud_clear_margins(struct vc_d info->fbops->fb_fillrect(info, ®ion); } - if (bh) { + if ((int) bh > 0) { region.dy = info->var.yoffset; region.dx = info->var.xoffset; region.height = bh;