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 9DD37C433F5 for ; Fri, 4 Feb 2022 12:23:46 +0000 (UTC) Received: from localhost ([::1]:39244 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nFxcv-0007j6-FJ for qemu-devel@archiver.kernel.org; Fri, 04 Feb 2022 07:23:45 -0500 Received: from eggs.gnu.org ([209.51.188.92]:40214) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nFxXC-0002cY-Lq; Fri, 04 Feb 2022 07:17:50 -0500 Received: from vmicros1.altlinux.org ([194.107.17.57]:38488) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nFxX9-0001nI-9O; Fri, 04 Feb 2022 07:17:50 -0500 Received: from mua.local.altlinux.org (mua.local.altlinux.org [192.168.1.14]) by vmicros1.altlinux.org (Postfix) with ESMTP id A8E4072C905; Fri, 4 Feb 2022 15:17:29 +0300 (MSK) Received: by mua.local.altlinux.org (Postfix, from userid 508) id 8575F7CD200; Fri, 4 Feb 2022 15:17:29 +0300 (MSK) Date: Fri, 4 Feb 2022 15:17:29 +0300 From: "Dmitry V. Levin" To: Vitaly Chikunov Subject: Re: [PATCH v3] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Message-ID: <20220204121729.GA16432@altlinux.org> References: <20220204050609.15510-1-vt@altlinux.org> <20220204121538.GA16340@altlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220204121538.GA16340@altlinux.org> Received-SPF: pass client-ip=194.107.17.57; envelope-from=ldv@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-stable@nongnu.org, Christian Schoenebeck , Greg Kurz , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Feb 04, 2022 at 03:15:38PM +0300, Dmitry V. Levin wrote: > On Fri, Feb 04, 2022 at 08:06:09AM +0300, 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) { > > + /* 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); > > +} > > Reviewed-by: Dmitry V. Levin" Reviewed-by: Dmitry V. Levin There should be no '"', sorry about that. :) -- ldv