From patchwork Sun Jul 12 11:10:13 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 11658049 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 C42F214E3 for ; Sun, 12 Jul 2020 11:10:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B56252070B for ; Sun, 12 Jul 2020 11:10:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728729AbgGLLKx (ORCPT ); Sun, 12 Jul 2020 07:10:53 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:50711 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725892AbgGLLKw (ORCPT ); Sun, 12 Jul 2020 07:10:52 -0400 Received: from fsav303.sakura.ne.jp (fsav303.sakura.ne.jp [153.120.85.134]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 06CBAKMo040327; Sun, 12 Jul 2020 20:10:20 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav303.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav303.sakura.ne.jp); Sun, 12 Jul 2020 20:10:20 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav303.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 06CBAFJP040301 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sun, 12 Jul 2020 20:10:19 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) From: Tetsuo Handa To: Greg Kroah-Hartman , Jiri Slaby Cc: Dmitry Vyukov , dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Tetsuo Handa Subject: [PATCH] fbdev: Detect integer underflow at "struct fbcon_ops"->clear_margins. Date: Sun, 12 Jul 2020 20:10:13 +0900 Message-Id: <20200712111013.11881-2-penguin-kernel@I-love.SAKURA.ne.jp> X-Mailer: git-send-email 2.18.4 In-Reply-To: <20200712111013.11881-1-penguin-kernel@I-love.SAKURA.ne.jp> References: <189fc902-db7c-9886-cc31-c0348435303a@i-love.sakura.ne.jp> <20200712111013.11881-1-penguin-kernel@I-love.SAKURA.ne.jp> Sender: linux-fbdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org I found 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); causes general protection fault in bitfill_aligned(), for vc_do_resize() updates vc->vc_{cols,rows} only when vc_do_resize() will return 0. [ 20.102222] BUG: unable to handle page fault for address: ffffb80500d7b000 [ 20.102225] #PF: supervisor write access in kernel mode [ 20.102226] #PF: error_code(0x0002) - not-present page [ 20.102227] PGD 13a48c067 P4D 13a48c067 PUD 13a48d067 PMD 132525067 PTE 0 [ 20.102230] Oops: 0002 [#1] SMP [ 20.102232] CPU: 3 PID: 2786 Comm: a.out Not tainted 5.8.0-rc4+ #749 [ 20.102233] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020 [ 20.102237] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect] [ 20.102277] Call Trace: [ 20.102281] cfb_fillrect+0x159/0x340 [cfbfillrect] [ 20.102747] vmw_fb_fillrect+0x12/0x30 [vmwgfx] [ 20.102755] bit_clear_margins+0x92/0xf0 [fb] [ 20.102760] fbcon_clear_margins+0x4c/0x50 [fb] [ 20.102763] fbcon_switch+0x321/0x570 [fb] [ 20.102771] redraw_screen+0xe0/0x250 [ 20.102775] fbcon_modechanged+0x164/0x1b0 [fb] [ 20.102779] fbcon_update_vcs+0x15/0x20 [fb] [ 20.102781] fb_set_var+0x364/0x3c0 [fb] [ 20.102817] do_fb_ioctl+0x2ff/0x3f0 [fb] [ 20.103139] fb_ioctl+0x2e/0x40 [fb] [ 20.103141] ksys_ioctl+0x86/0xc0 [ 20.103146] __x64_sys_ioctl+0x15/0x20 [ 20.103148] do_syscall_64+0x54/0xa0 [ 20.103151] entry_SYSCALL_64_after_hwframe+0x44/0xa9 If vc_do_resize() fails (e.g. kzalloc() failure) when var.xres or var.yres is going to shrink, bit_clear_margins() hits integer underflow bug due to 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. This crash is easily reproducible by calling vc_do_resize(vc, 0, 0) which the reproducer above will do. Since fbcon_modechanged() is doing 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); (...snipped...) update_screen(vc); , var.xres < vc->vc_font.width makes cols = 0 and var.yres < vc->vc_font.height makes rows = 0. But vc_do_resize() does not set vc->vc_cols = vc->vc_rows = 0 due to new_cols = (cols ? cols : vc->vc_cols); new_rows = (lines ? lines : vc->vc_rows); exception. Of course, the root problem is that callers of do_vc_resize() are not handling vc_do_resize() failures, but it might not be easy to handle them under complicated dependency. 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. I hope that we can survive even if info->var.{xres,yres} were increased but vc->vc_{cols,rows} were not increased due to kzalloc() failure, for the __iomem memory for cfb_fillrect() seems to be allocated upon driver load. By the way, syzbot has several reports which are stalling inside filling functions. Although reproducer for [1] is not found yet, it has tried r0 = openat$fb0(0xffffffffffffff9c, &(0x7f0000000180)='/dev/fb0\x00', 0x0, 0x0) ioctl$FBIOPUT_VSCREENINFO(r0, 0x4601, &(0x7f0000000000)={0x0, 0x0, 0x0, 0x500, 0x0, 0x0, 0x4}) which corresponds to const int fd = open("/dev/fb0", O_ACCMODE); struct fb_var_screeninfo var = { }; var.yres_virtual = 0x500; var.bits_per_pixel = 4; ioctl(fd, FBIOPUT_VSCREENINFO, &var); and somehow hit unexpectedly long bit_clear_margins() loops. I don't know why syzbot does not hit general protection fault, but it would depend on environment because in my VMware environment ioctl(FBIOPUT_VSCREENINFO) returns -EINVAL if var.xres == var.yres == 0. [1] https://syzkaller.appspot.com/bug?id=91ecc3bf32ab1a551c33a39dab7fc0c8cd7b7e16 Signed-off-by: Tetsuo Handa --- 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;