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 EF66BC433EF for ; Fri, 4 Feb 2022 15:41:13 +0000 (UTC) Received: from localhost ([::1]:59170 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nG0i0-000165-Ul for qemu-devel@archiver.kernel.org; Fri, 04 Feb 2022 10:41:12 -0500 Received: from eggs.gnu.org ([209.51.188.92]:60842) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nG0aQ-0006qA-Tx; Fri, 04 Feb 2022 10:33:23 -0500 Received: from kylie.crudebyte.com ([5.189.157.229]:44931) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nG0aO-0004zh-6O; Fri, 04 Feb 2022 10:33:22 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=kylie; h=Content-Type:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Content-ID:Content-Description; bh=ocNeoNP9HxkIfK1BFJyxZpPZSTBGxTw03GlWfmFlDrY=; b=BbzDtERjCgqRtNSSZrm5f3feNq GxFksKmWhVOxArfFRloN6N+DK1rK+guDWqKxNwqCJdapi+ax/8fn7cUx+Lu0kzHjEoQdye1DqKW24 n/n15X9ygtzxfRCPTc5NS1xpZnOZBVnqSM5Zgvi9oDJIvJc76cFICA+D92UmavBn1X3BgFRZjVw4S GvV7AjYEqV3zlpaGTKtKTqLR2VcKZjsvIX+CQDScOskhYXKbsXNNc6yDMFU+RAZsl0cIh6Sk0Fp6x XkdJA9lETT8K2FZxVKWmkHQOzA8OqkW93YFeWWzx1tzx7mmghlIayYoZK73fOopi11CGQ2oEVdiFU leDUL+7o9XptxkRK5DSUd0mRBlmTgPKnj6fXbTnNNTUcBF5L/OqOhXvZzYZlqc3aS+Ry6Iszhj7SW dvz1Qy/ZXTH6PHYtCBAtjjxuzedL5gks9NBCuIerB/I4MtdFAIjeAhGN8FdpR08KbBV6oT1eQt9sj 7jeRZjrm6okQgO3upijmVlJifkt7YtdwjbeUbN+iG2aGGb6ETh9uzpohPVg0NXAUHR0XpbMLkWV8d Co5BIPXftzSr7cInlnQ4JeE2oa7jBcDFgSEOkbO1J2FHeika0U+wCm3TDV2mZN82l6j0C574rSPXP EEKRlflctYsgR85jU3WQW30COf6ffJmv/jlGG9rfk=; From: Christian Schoenebeck To: Greg Kurz Cc: qemu-devel@nongnu.org, Philippe =?ISO-8859-1?Q?Mathieu=2DDaud=E9?= , Vitaly Chikunov , qemu-stable@nongnu.org, ldv@altlinux.org Subject: Re: [PATCH v3] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Date: Fri, 04 Feb 2022 16:33:13 +0100 Message-ID: <2106305.L43djaopl2@silver> In-Reply-To: <20220204161606.162d2c05@bahia> References: <20220204050609.15510-1-vt@altlinux.org> <28345882.VnrBaU8NEn@silver> <20220204161606.162d2c05@bahia> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" Received-SPF: pass client-ip=5.189.157.229; envelope-from=qemu_oss@crudebyte.com; helo=kylie.crudebyte.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Freitag, 4. Februar 2022 16:16:06 CET Greg Kurz wrote: > On Fri, 04 Feb 2022 15:12:18 +0100 >=20 > Christian Schoenebeck wrote: > > On Freitag, 4. Februar 2022 14:55:45 CET Philippe Mathieu-Daud=E9 via w= rote: > > > On 4/2/22 06:06, Vitaly Chikunov wrote: > > > > `struct dirent' returned from readdir(3) could be shorter (or longe= r) > > > > than `sizeof(struct dirent)', thus memcpy of sizeof length will > > > > overread > > > >=20 > > > > 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) > > > >=20 > > > > While fixing, provide a helper for any future `struct dirent' cloni= ng. > > > >=20 > > > > 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. > > > >=20 > > > > Changes from v2: > > > > - Make it work with a simulated dirent where d_reclen is 0, which w= as > > > >=20 > > > > caused abort in readdir qos-test, by using fallback at runtime. > > > > =20 > > > > hw/9pfs/codir.c | 3 +-- > > > > include/qemu/osdep.h | 13 +++++++++++++ > > > > util/osdep.c | 18 ++++++++++++++++++ > > > > 3 files changed, 32 insertions(+), 2 deletions(-) > > > >=20 > > > > +struct dirent * > > > > +qemu_dirent_dup(struct dirent *dent) > > > > +{ > > > > + size_t sz =3D 0; > > > > +#if defined _DIRENT_HAVE_D_RECLEN > > > > + /* Avoid use of strlen() if there's d_reclen. */ > > > > + sz =3D dent->d_reclen; > > > > +#endif > > > > + if (sz =3D=3D 0) { > > >=20 > > > If _DIRENT_HAVE_D_RECLEN is defined, this case is unlikely... > > >=20 > > > > + /* Fallback to the most portable way. */ > > > > + sz =3D offsetof(struct dirent, d_name) + > > > > + strlen(dent->d_name) + 1; > > > > + } > > > > + struct dirent *dst =3D g_malloc(sz); > > > > + return memcpy(dst, dent, sz); > > > > +} > > >=20 > > > What about this? > > >=20 > > > struct dirent * > > > qemu_dirent_dup(struct dirent *dent) > > > { > > >=20 > > > size_t sz; > > >=20 > > > #if defined _DIRENT_HAVE_D_RECLEN > > >=20 > > > /* Avoid use of strlen() if there's d_reclen. */ > > > sz =3D dent->d_reclen; > > >=20 > > > #else > > >=20 > > > /* Fallback to the most portable way. */ > > > sz =3D offsetof(struct dirent, d_name) + > > > =20 > > > strlen(dent->d_name) + 1; > > >=20 > > > #endif > > >=20 > > > return g_memdup(dent, sz); > > >=20 > > > } > >=20 > > That was the intentional change v2 -> v3 Philippe. Previous v2 crashed = the > > 9p 'synth' tests: > >=20 > > https://lore.kernel.org/qemu-devel/2627488.0S70g7mNYN@silver/T/#ma09bed= de5 > > 9a91e6435443e151f7e49fef8616e4c > >=20 > > You might argue that the 9p 'synth' driver should instead populate > > d_reclen > > instead, but this v3 is a simpler solution and guarantees to always wor= k. > > So I'd prefer to go with Vitaly's v3 for now, especially as this patch > > would go to the stable branches as well. >=20 > This really is a band-aid. Anyone reading this will react as Philippe, > and this is common code, not just 9pfs. With correctly populated dirents, > the helper could be as simple as: >=20 > struct dirent * > qemu_dirent_dup(struct dirent *dent) > { > size_t sz =3D offsetof(struct dirent, d_name) + _D_EXACT_NAMLEN(dent)= + 1; >=20 > return g_memdup(dent, sz); > } Which requires _D_EXACT_NAMLEN being defined, whereas Vitaly's solution=20 ensures to work on all systems. > If this is a cycles problem, I can help reviewing the fixes on > the synth driver, or alternatively you can keep this code > somewhere under 9pfs but please don't put that in common utils. Who cares, sends a patch, and makes sure that it works at least as reliably= as=20 the currently suggested solution (tested with guest and test cases). Thanks! Best regards, Christian Schoenebeck