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 87119C433EF for ; Fri, 28 Jan 2022 14:48:31 +0000 (UTC) Received: from localhost ([::1]:54466 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nDSYA-0007qn-6u for qemu-devel@archiver.kernel.org; Fri, 28 Jan 2022 09:48:30 -0500 Received: from eggs.gnu.org ([209.51.188.92]:44724) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nDST9-000509-KP; Fri, 28 Jan 2022 09:43:19 -0500 Received: from kylie.crudebyte.com ([5.189.157.229]:51365) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nDST7-00077e-BF; Fri, 28 Jan 2022 09:43:19 -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=JYjTsyZIW4dQuxOM7l2Jhw6FAHsHet+TdfpRGowNRnw=; b=HUsSsKbyNfkeNNVN4JksfK3loD lYVBykFccSxuuz5favWehB/L3BBpBszBDSisYhRdmxA16uWxJzNYy/lWpG9qOl+hD8oXoyHwU3TFg GWCMt3YWQxuhZwjl23cW5VsA3mZgHoOF1iRuF1wwERtoQiEkFxSaq7OgfibRwknPCAHIm0/qou2ZQ kvYTMGD4lwrNogt3QxgY5qNudWEtp6xtQn/j7OeYCupKPTJuySznrBPnqwwUsWXBmNf5f4pz91NEp vWxHvl0IL1UPJ2Ry3VdqnzRSisrsg5BzrdZYyVkTX7u24Ka2neu1ToMmJDuCuBfS632vwzojrMSyq pTs5dD3ZdLvmg7pcN58R27LOWlKV5ItX/Z+u1DRgVAAZJRkAK9BA6T7rGc3YnahE5EmGq8wkLI5mp o4itNqiQGksFqPF/+asbr3GcaSB8uNlTTn4sS31+D/OYHmeAUDUKR0XsrjL42gT1gVficHWqb7NZt wn1po4eP9UxknZoi6SylQDsmXJQSHuaiinoPRaN4mr5PzWEDbCcRrcK7UXt72+dImJHb7Px2dVM4a HnnGd0/lxqIlGpTyJhjiKLmUCh6r3BEWbh9xH5sePSexGMmMzRfktcHdeDoIfafQb3dhwuS4tirsJ PPdg0PUIQE/tbIena19VWhTASvom+QhOnX7y51IEA=; From: Christian Schoenebeck To: qemu-devel@nongnu.org Cc: Vitaly Chikunov , Greg Kurz , ldv@altlinux.org, qemu-stable@nongnu.org Subject: Re: [PATCH] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Date: Fri, 28 Jan 2022 15:43:10 +0100 Message-ID: <2533498.9Ea8Rob0xc@silver> In-Reply-To: <20220127212734.218900-1-vt@altlinux.org> References: <20220127212734.218900-1-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 Donnerstag, 27. Januar 2022 22:27:34 CET Vitaly Chikunov wrote: > `struct dirent' returned from readdir(3) could be shorter than > `sizeof(struct dirent)', thus memcpy of sizeof length will overread > into unallocated page causing SIGSEGV. Example stack trace: It could be shorter or longer. Your patch is fixing both possibilities. I just realized BTW that there are other places that should be fixed as well. :/ For instance hw/9pfs/9p-synth.c (used for the 9p test cases [1][2]) is copying dirents, too. And in hw/9pfs/9p.c v9fs_do_readdir_with_stat() used by 9p2000.u doesn't even bother to copy at all, which is undefined behaviour as fs driver is running on a background thread and the dirent pointer might have mutated in the meantime with the next readdir() call. [1] https://wiki.qemu.org/Documentation/9p#Test_Cases [2] https://wiki.qemu.org/Documentation/9p#9p_Filesystem_Drivers > #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) > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > Signed-off-by: Vitaly Chikunov Adding qemu-stable on CC for making sure this patch will be handled for the stable branches as well. > --- > Tested on x86-64 Linux. > > hw/9pfs/codir.c | 7 +++++-- > include/qemu/osdep.h | 6 ++++++ > util/osdep.c | 23 +++++++++++++++++++++++ > 3 files changed, 34 insertions(+), 2 deletions(-) > > diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c > index 032cce04c4..ea7f5e6578 100644 > --- a/hw/9pfs/codir.c > +++ b/hw/9pfs/codir.c > @@ -143,8 +143,11 @@ 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); That's the actual fix. > + if (!e->dent) { > + err = -errno; > + break; > + } e->dent is never NULL, so this check can be removed. See explanation about g_malloc() below. > > /* 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..b54d22db04 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -805,6 +805,12 @@ static inline int > platform_does_not_support_system(const char *command) } > #endif /* !HAVE_SYSTEM_FUNCTION */ > > +/** > + * Actual 'struct dirent' size may be bigger or shorter than > + * sizeof(struct dirent) in many cases. > + */ > +struct dirent *qemu_dirent_dup(struct dirent *dent); > + I think this issue deserves a more verbose API doc comment, something like: /** * 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..e39d1071fd 100644 > --- a/util/osdep.c > +++ b/util/osdep.c > @@ -33,6 +33,7 @@ > extern int madvise(char *, size_t, int); > #endif > > +#include Wouldn't that break Windows builds? > #include "qemu-common.h" > #include "qemu/cutils.h" > #include "qemu/sockets.h" > @@ -615,3 +616,25 @@ 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) > +{ > + struct dirent *dst; > +#if defined _DIRENT_HAVE_D_RECLEN > + /* Avoid use of strlen() if there's d_reclen. */ > + dst = g_malloc(dent->d_reclen); > +#else > + /* Fallback to a most portable way. */ > + const size_t reclen = offsetof(struct dirent, d_name) + > strlen(dent->d_name) + 1; + > + dst = g_malloc(reclen); > +#endif > + if (!dst) > + return NULL; > +#ifdef _DIRENT_HAVE_D_RECLEN > + return memcpy(dst, dent, dent->d_reclen); > +#else > + return memcpy(dst, dent, reclen); > +#endif > +} On the long run we probably should have a configure check whether d_reclen exists, but I would not insist on that now as there is a valid fallback solution at least. Note that g_malloc() never returns NULL, if it runs out of memory it terminates instead, so the NULL checks are unncessary: https://developer.gimp.org/api/2.0/glib/glib-Memory-Allocation.html#g-try-malloc Also I would prefer g_malloc0() over g_malloc(). Then by adding a variable for the d_reclen yes/no case, overall code can be reduced. So I would suggest something like this instead: struct dirent * qemu_dirent_dup(struct dirent *dent) { #if defined _DIRENT_HAVE_D_RECLEN /* Avoid use of strlen() if there's d_reclen. */ const size_t sz = dent->d_reclen; #else /* Fallback to a most portable way. */ const size_t sz = offsetof(struct dirent, d_name) + strlen(dent->d_name) + 1; #endif struct dirent *dst = g_malloc(sz); return memcpy(dst, dent, sz); } Best regards, Christian Schoenebeck