From nobody Sat Feb 7 23:34:06 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 16439513045428.045754795100606; Thu, 3 Feb 2022 21:08:24 -0800 (PST) Received: from localhost ([::1]:48752 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nFqpb-0005m8-4f for importer@patchew.org; Fri, 04 Feb 2022 00:08:23 -0500 Received: from eggs.gnu.org ([209.51.188.92]:48044) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nFqnp-0004Yl-45; Fri, 04 Feb 2022 00:06:33 -0500 Received: from vmicros1.altlinux.org ([194.107.17.57]:53258) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nFqnm-0000dk-Fx; Fri, 04 Feb 2022 00:06:32 -0500 Received: from imap.altlinux.org (imap.altlinux.org [194.107.17.38]) by vmicros1.altlinux.org (Postfix) with ESMTP id E543B72C905; Fri, 4 Feb 2022 08:06:25 +0300 (MSK) Received: from beacon.altlinux.org (unknown [193.43.10.9]) by imap.altlinux.org (Postfix) with ESMTPSA id B8F5D4A46F0; Fri, 4 Feb 2022 08:06:25 +0300 (MSK) From: Vitaly Chikunov To: Greg Kurz , Christian Schoenebeck , qemu-devel@nongnu.org Subject: [PATCH v3] 9pfs: Fix segfault in do_readdir_many caused by struct dirent overread Date: Fri, 4 Feb 2022 08:06:09 +0300 Message-Id: <20220204050609.15510-1-vt@altlinux.org> X-Mailer: git-send-email 2.33.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.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: Vitaly Chikunov , qemu-stable@nongnu.org, ldv@altlinux.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZM-MESSAGEID: 1643951308611100001 Content-Type: text/plain; charset="utf-8" `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 + 0x4982e= 9) #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 Reviewed-by: Christian Schoenebeck Reviewed-by: Dmitry V. Levin Reviewed-by: Dmitry V. Levin" --- 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 =3D e->next =3D g_malloc0(sizeof(V9fsDirEnt)); } - e->dent =3D g_malloc0(sizeof(struct dirent)); - memcpy(e->dent, dent, sizeof(struct dirent)); + e->dent =3D qemu_dirent_dup(dent); =20 /* perform a full stat() for directory entry if requested by calle= r */ 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(con= st char *command) } #endif /* !HAVE_SYSTEM_FUNCTION */ =20 +/** + * 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 =20 +#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 =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) { + /* 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 2.33.0