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 81AE3C433EF for ; Sat, 5 Feb 2022 11:39:38 +0000 (UTC) Received: from localhost ([::1]:44322 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nGJPl-0002o3-0X for qemu-devel@archiver.kernel.org; Sat, 05 Feb 2022 06:39:37 -0500 Received: from eggs.gnu.org ([209.51.188.92]:54684) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nGJNG-0000yy-1i; Sat, 05 Feb 2022 06:37:02 -0500 Received: from kylie.crudebyte.com ([5.189.157.229]:54423) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nGJND-0004LL-8k; Sat, 05 Feb 2022 06:37:01 -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=p3+Fr0k89qkEVGP4YS5bZESV/zuXNUO83P/Yku6caaY=; b=uMRrzOfP/GpBHVbPDzhyaX7TcA bazdZbMwoaAqc/idGzTcTK3nKgjKQKp7N5s0Q1g68lYYS/cD7qL/Z2Tidu5+gloOfCBVXmlLf3PGX jrXW3YSjigvERPIh/hyJh3fSCjf/DzvHLG0znrmyarm389gfeQqUVqpZIeWyCN/wpB1ua909Q6nzb 85lYAVb2L0A/GrtWSun9bAdRTyyIx3lEV0LH+2W1Zl1wS2i7yf+vcGJfpqyGLJvqaEPypRrLm2uVS Dupzb1nTYP+U0ZnYQSytFKu6d4GD5l+zDn2OHPjzJ/IijNq8oe3zpsFPJYTFkbDOuj15nyPXDxUZ8 vLh6pcEAC12VAdgK4h0HCo5ZqszemcEnu/Rm/MgnEj5yI1st1xii6XL1JyYrfuB65qVf4raE34B2x vtz9ooaU25gjoWqJE0T0tmPxdbATQzntsJxMEbxmapHKE6uEM2mziOuROSeCTFpuREQngHxDegXHP ffBqFif6529jb+fpGdSnXI56uwaq06QEaxc4E9bVV5US4zzBI92Yye2Wk3M4JVpiMdddLlFyNuIW6 Jq25M2ckh4vwLmuiq3cvXwkQrHs5TDi6Yn7u8iGYM5g7c66KxCf2Y9TLHzgQsJhoJFk2uE3EFo25q 33dQ3EC9w9B7fiCDSyf36Db8dbTZqBf/2bL7PzyT0=; From: Christian Schoenebeck To: qemu-devel@nongnu.org, Philippe =?ISO-8859-1?Q?Mathieu=2DDaud=E9?= via Cc: Vitaly Chikunov , Greg Kurz , qemu-stable@nongnu.org, ldv@altlinux.org Subject: Re: [PATCH v3] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Date: Sat, 05 Feb 2022 12:36:55 +0100 Message-ID: <2519450.KGbbELgHQX@silver> In-Reply-To: <20220204050609.15510-1-vt@altlinux.org> References: <20220204050609.15510-1-vt@altlinux.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" 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 06:06:09 CET 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(-) > > diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c > index 032cce04c4..c0873bde16 100644 > --- a/hw/9pfs/codir.c > +++ b/hw/9pfs/codir.c > @@ -143,8 +143,7 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState > *fidp, } else { > e = e->next = g_malloc0(sizeof(V9fsDirEnt)); > } > - e->dent = g_malloc0(sizeof(struct dirent)); > - memcpy(e->dent, dent, sizeof(struct dirent)); > + e->dent = qemu_dirent_dup(dent); > > /* perform a full stat() for directory entry if requested by caller > */ if (dostat) { > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > index d1660d67fa..ce12f64853 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -805,6 +805,19 @@ static inline int > platform_does_not_support_system(const char *command) } > #endif /* !HAVE_SYSTEM_FUNCTION */ > > +/** > + * Duplicate directory entry @dent. > + * > + * It is highly recommended to use this function instead of open coding > + * duplication of @c dirent objects, because the actual @c struct @c dirent > + * size may be bigger or shorter than @c sizeof(struct dirent) and correct > + * handling is platform specific (see gitlab issue #841). > + * > + * @dent - original directory entry to be duplicated > + * @returns duplicated directory entry which should be freed with g_free() > + */ > +struct dirent *qemu_dirent_dup(struct dirent *dent); > + > #ifdef __cplusplus > } > #endif > diff --git a/util/osdep.c b/util/osdep.c > index 42a0a4986a..2c80528a61 100644 > --- a/util/osdep.c > +++ b/util/osdep.c > @@ -33,6 +33,7 @@ > extern int madvise(char *, size_t, int); > #endif > > +#include > #include "qemu-common.h" > #include "qemu/cutils.h" > #include "qemu/sockets.h" > @@ -615,3 +616,20 @@ writev(int fd, const struct iovec *iov, int iov_cnt) > return readv_writev(fd, iov, iov_cnt, true); > } > #endif > + > +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) { Philippe, Greg, apart from the additional comment, do you want to see this check to be changed in v4 to this? if (unlikely(sz == 0)) { Best regards, Christian Schoenebeck > + /* Fallback to the most portable way. */ > + sz = offsetof(struct dirent, d_name) + > + strlen(dent->d_name) + 1; > + } > + struct dirent *dst = g_malloc(sz); > + return memcpy(dst, dent, sz); > +}