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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 B4B8CC2D0A8 for ; Sat, 26 Sep 2020 19:40:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64E55221EA for ; Sat, 26 Sep 2020 19:40:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Aqu4Vvvc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730176AbgIZTkH (ORCPT ); Sat, 26 Sep 2020 15:40:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41580 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729291AbgIZTkG (ORCPT ); Sat, 26 Sep 2020 15:40:06 -0400 Received: from mail-pf1-x444.google.com (mail-pf1-x444.google.com [IPv6:2607:f8b0:4864:20::444]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E131AC0613CE; Sat, 26 Sep 2020 12:40:06 -0700 (PDT) Received: by mail-pf1-x444.google.com with SMTP id x22so5991926pfo.12; Sat, 26 Sep 2020 12:40:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=z/Wf/3QHi80/sQfmdSfCdx2ZY+b1si1Ve9CIncWZLPc=; b=Aqu4VvvcLLk8HRAROUrSqzdPdruCf748+CbScaaqaVpUZOmVe5KHuLzgjLAUbmXs3t vzhSzKDX7QJh092q8/yOtbNLGv5fYkBGp5RlZ/pmc6PSELNxK0uHhvPimuv+qygP9fwj ytRePrY9vej5lD0YjDMxX7WyrBpm7G9QnzS+kZBwhX8udZvh/wfHUwYN8DuVboYwmUwt 5wc/bKjQKp+IvFsvlsVrefOFP8w0n/xVWhrakv2bnuywehSIJKIJwh5Dbq5e0cfwqeNv ZcVp0SxthLG152MZvD3saw2RfTCc3m887GGs7sTu96v1HVu3wDGBBn6Hjw0F1fYLb/pw r6Ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=z/Wf/3QHi80/sQfmdSfCdx2ZY+b1si1Ve9CIncWZLPc=; b=YxeQ67CJ/KMzJihDL9BzULAozaWzvh8wvvbOkABIlH0aCAL+fPNqYFKqQfv7q6kCNJ 1aXlFvw0n33TzPZmmO1Ky28hkRApnrjVXO8z+EixA1BNZ1TrM8Edv81NTn72uqHoDrQu ouIJjmyB/CRUX3Wgo6e4av4eSG0JRn0qHdn+oe9By8RoGcc3Rc6liA0Kc1Jr+6UybKmi inaZKxNmdJXL+ujak/Y5qoo9nmc0uvBpvh/+CYDtHWEDF6qel12WYWFiHR47SXomOvDy utaZieK9LS8XhzLG/Ela13kzLzzgXIEa8lRb/dXukstMhUqGYis+H94+Ym5dSboRRf0j WH0A== X-Gm-Message-State: AOAM530LSPGSQuuydSVLQpoCglxFNo9wE4gwcryugd4Nn0cyHoS6Ka+8 jtmujwNYYSzPmJMKVtMbLigRp/N+Hz8ochA= X-Google-Smtp-Source: ABdhPJx++z5PLIkM2jj3Fb7/bzZyOIB/WkNavwfESpUe2Pl7KYRs/XdphoGaWDKJtwgYKU/tQtJqbg== X-Received: by 2002:a62:4ed6:0:b029:142:2501:35ec with SMTP id c205-20020a624ed60000b0290142250135ecmr4801624pfb.76.1601149206406; Sat, 26 Sep 2020 12:40:06 -0700 (PDT) Received: from PWN ([161.117.41.183]) by smtp.gmail.com with ESMTPSA id s70sm5557357pgc.11.2020.09.26.12.40.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 26 Sep 2020 12:40:05 -0700 (PDT) Date: Sat, 26 Sep 2020 15:39:57 -0400 From: Peilin Ye To: Tetsuo Handa Cc: syzbot , b.zolnierkie@samsung.com, daniel.vetter@ffwll.ch, deller@gmx.de, gregkh@linuxfoundation.org, jirislaby@kernel.org, syzkaller-bugs@googlegroups.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, yepeilin.cs@gmail.com Subject: Re: KASAN: use-after-free Read in bit_putcs Message-ID: <20200926193957.GA1033221@PWN> References: <000000000000226d3f05b02dd607@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 27, 2020 at 01:25:17AM +0900, Tetsuo Handa wrote: > A simplified reproducer and debug printk() patch shown below reported that > vc_font.height is increased to 9 via ioctl(VT_RESIZEX) after it was once > decreased from 16 to 2 via ioctl(PIO_FONT). > > > > Since vc_resize() with v.v_rows == 0 preserves current vc->vc_rows value, > this reproducer is bypassing > > if (v.v_clin) { > int rows = v.v_vlin / v.v_clin; > if (v.v_rows != rows) { > if (v.v_rows) /* Parameters don't add up */ > return -EINVAL; > v.v_rows = rows; > } > } > > check by setting v.v_vlin == 1 and v.v_clin == 9. > > If v.v_vcol > 0 and v.v_vcol != vc->vc_cols (though this reproducer is passing > v.v_vcol == 0), tty_do_resize() from vc_do_resize() from vc_resize() can make > "struct tty_struct"->winsize.ws_ypixel = 1 despite > "struct tty_struct"->winsize.vc->vc_rows = vc->vc_rows (which is usually larger > than 1). Does such winsize (a row has 1 / vc->vc_rows pixel) make sense? > > > > Since I don't know the meaning of "struct vt_consize"->v_clin (which is commented > with "/* number of pixel rows per character */" but does it mean font size ?), > I don't know why we can assign that value to vcp->vc_font.height via > > if (v.v_clin) > vcp->vc_font.height = v.v_clin; > > in vt_resizex(). While ioctl(PIO_FONT) needs to pass vc->vc_sw->con_font_set() > check in con_font_set(), ioctl(VT_RESIZEX) does not pass it in vt_resizex()... > > Since this problem does not happen if I remove > > if (v.v_clin) > vcp->vc_font.height = v.v_clin; Hi Tetsuo! > from vt_resizex(), I guess that some variables are getting confused by change > of vc->vc_font.height ... Yes, see bit_putcs(): (drivers/video/fbdev/core/bitblit.c) static void bit_putcs(struct vc_data *vc, struct fb_info *info, const unsigned short *s, int count, int yy, int xx, int fg, int bg) { struct fb_image image; u32 width = DIV_ROUND_UP(vc->vc_font.width, 8); u32 cellsize = width * vc->vc_font.height; ^^^^^^^^ ^^^^^^^^^^^^^^ `cellsize` is now too large. Later, in bit_putcs_aligned(): while (cnt--) { src = vc->vc_font.data + (scr_readw(s++)& charmask)*cellsize; ^^^^^^^^ `src` goes out of bounds of the data buffer. At first glance I guess this is an out-of-bound read reported as a use-after-free read? The crashlog says: [ 149.732103][ T6693] Allocated by task 6667: [ 149.732115][ T6693] kasan_save_stack (mm/kasan/common.c:48) [ 149.732121][ T6693] __kasan_kmalloc.constprop.0 (mm/kasan/common.c:56 mm/kasan/common.c:461) [ 149.732126][ T6693] __kmalloc (mm/slab.c:3656 mm/slab.c:3664) [ 149.732133][ T6693] alloc_pipe_info (fs/pipe.c:810) [ 149.732139][ T6693] create_pipe_files (fs/pipe.c:883 fs/pipe.c:914) [ 149.732145][ T6693] do_pipe2 (fs/pipe.c:965 fs/pipe.c:1012) I'm not sure, but I don't think a buffer allocated in fs/pipe.c is related here. Maybe they just live near each other on the heap? To resolve this out-of-bound issue for now, I think the easiest way is to add a range check in bit_putcs(), or bit_putcs_aligned(). ...but yeah, that `VT_RESIZEX` ioctl looks really buggy, and is already causing more issues: KASAN: global-out-of-bounds Read in fbcon_get_font Link: https://syzkaller.appspot.com/bug?id=08b8be45afea11888776f897895aef9ad1c3ecfd This was also caused by `VT_RESIZEX`... Thank you, Peilin Ye