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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4E033C433F5 for ; Sat, 5 Feb 2022 03:25:59 +0000 (UTC) Received: from localhost ([::1]:50092 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nGBi1-0003eB-Po for qemu-devel@archiver.kernel.org; Fri, 04 Feb 2022 22:25:57 -0500 Received: from eggs.gnu.org ([209.51.188.92]:59148) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nGBgH-0002dr-SG; Fri, 04 Feb 2022 22:24:09 -0500 Received: from vmicros1.altlinux.org ([194.107.17.57]:39394) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nGBg3-0007UU-9D; Fri, 04 Feb 2022 22:23:58 -0500 Received: from imap.altlinux.org (imap.altlinux.org [194.107.17.38]) by vmicros1.altlinux.org (Postfix) with ESMTP id 203F672C905; Sat, 5 Feb 2022 06:23:51 +0300 (MSK) Received: from altlinux.org (sole.flsd.net [185.75.180.6]) by imap.altlinux.org (Postfix) with ESMTPSA id 07E6A4A46F0; Sat, 5 Feb 2022 06:23:51 +0300 (MSK) Date: Sat, 5 Feb 2022 06:23:50 +0300 From: Vitaly Chikunov To: "Dmitry V. Levin" Subject: Re: [PATCH v3] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Message-ID: <20220205032350.7lmmknm7zimaew5w@altlinux.org> References: <20220204050609.15510-1-vt@altlinux.org> <449c9c55-06e8-66ef-8755-3ab2e785851c@amsat.org> <20220204161939.GC18407@altlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220204161939.GC18407@altlinux.org> Received-SPF: pass client-ip=194.107.17.57; envelope-from=vt@altlinux.org; helo=vmicros1.altlinux.org X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, qemu-stable@nongnu.org, Christian Schoenebeck , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Greg Kurz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Feb 04, 2022 at 07:19:39PM +0300, Dmitry V. Levin wrote: > On Fri, Feb 04, 2022 at 02:55:45PM +0100, Philippe Mathieu-Daudé wrote: > > On 4/2/22 06:06, Vitaly Chikunov wrote: > > > `struct dirent' returned from readdir(3) could be shorter (or longer) > > > than `sizeof(struct dirent)', thus memcpy of sizeof length will overread > > > into unallocated page causing SIGSEGV. Example stack trace: > > > > > > #0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + 0x497eed) > > > #1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 + 0x4982e9) > > > #2 0x0000555555eb7983 coroutine_trampoline (/usr/bin/qemu-system-x86_64 + 0x963983) > > > #3 0x00007ffff73e0be0 n/a (n/a + 0x0) > > > > > > While fixing, provide a helper for any future `struct dirent' cloning. > > > > > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > > > Cc: qemu-stable@nongnu.org > > > Co-authored-by: Christian Schoenebeck > > > Signed-off-by: Vitaly Chikunov > > > --- > > > Tested on x86-64 Linux again. > > > > > > Changes from v2: > > > - Make it work with a simulated dirent where d_reclen is 0, which was > > > caused abort in readdir qos-test, by using fallback at runtime. > > > > > > hw/9pfs/codir.c | 3 +-- > > > include/qemu/osdep.h | 13 +++++++++++++ > > > util/osdep.c | 18 ++++++++++++++++++ > > > 3 files changed, 32 insertions(+), 2 deletions(-) > > > > > +struct dirent * > > > +qemu_dirent_dup(struct dirent *dent) > > > +{ > > > + size_t sz = 0; > > > +#if defined _DIRENT_HAVE_D_RECLEN > > > + /* Avoid use of strlen() if there's d_reclen. */ > > > + sz = dent->d_reclen; > > > +#endif > > > + if (sz == 0) { > > > > If _DIRENT_HAVE_D_RECLEN is defined, this case is unlikely... > > If it was so easy to be misled this way, > I'd suggest adding an explicit comment, e.g. > > /* > * Test sz for non-zero even if d_reclen is available > * because some drivers may set d_reclen to zero. > */ Sounds good, to avoid misunderstanding. I can send v4, with g_memdup (like Greg suggested). Thanks, > > > -- > ldv