From patchwork Wed Jul 15 01:51:02 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 11663985 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A4F2C722 for ; Wed, 15 Jul 2020 01:51:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 970612071B for ; Wed, 15 Jul 2020 01:51:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728061AbgGOBvL (ORCPT ); Tue, 14 Jul 2020 21:51:11 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:61272 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726356AbgGOBvL (ORCPT ); Tue, 14 Jul 2020 21:51:11 -0400 Received: from fsav302.sakura.ne.jp (fsav302.sakura.ne.jp [153.120.85.133]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 06F1p74Y092199; Wed, 15 Jul 2020 10:51:07 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav302.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav302.sakura.ne.jp); Wed, 15 Jul 2020 10:51:07 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav302.sakura.ne.jp) Received: from localhost.localdomain (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 06F1p2pR092141 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 15 Jul 2020 10:51:07 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) From: Tetsuo Handa To: Bartlomiej Zolnierkiewicz Cc: Greg Kroah-Hartman , Jiri Slaby , Dmitry Vyukov , George Kennedy , Dan Carpenter , dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Tetsuo Handa , syzbot Subject: [PATCH v2] fbdev: Detect integer underflow at "struct fbcon_ops"->clear_margins. Date: Wed, 15 Jul 2020 10:51:02 +0900 Message-Id: <20200715015102.3814-1-penguin-kernel@I-love.SAKURA.ne.jp> X-Mailer: git-send-email 2.18.4 In-Reply-To: References: Sender: linux-fbdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org 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 --- 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(-) diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c index ca935c09a261..35ebeeccde4d 100644 --- 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_data *vc, struct fb_info *info, 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_data *vc, struct fb_info *info, 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; diff --git a/drivers/video/fbdev/core/fbcon_ccw.c b/drivers/video/fbdev/core/fbcon_ccw.c index dfa9a8aa4509..78f3a5621478 100644 --- 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_data *vc, struct fb_info *info, 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_data *vc, struct fb_info *info, 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; diff --git a/drivers/video/fbdev/core/fbcon_cw.c b/drivers/video/fbdev/core/fbcon_cw.c index ce08251bfd38..fd098ff17574 100644 --- 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_data *vc, struct fb_info *info, 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_data *vc, struct fb_info *info, 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; diff --git a/drivers/video/fbdev/core/fbcon_ud.c b/drivers/video/fbdev/core/fbcon_ud.c index 1936afc78fec..e165a3fad29a 100644 --- 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_data *vc, struct fb_info *info, 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_data *vc, struct fb_info *info, 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;