From nobody Thu Nov 6 18:57:29 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1488238224591328.7699809156702; Mon, 27 Feb 2017 15:30:24 -0800 (PST) Received: from localhost ([::1]:57574 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciUkJ-0000Tv-87 for importer@patchew.org; Mon, 27 Feb 2017 18:30:23 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47125) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciUHv-0000jW-Kv for qemu-devel@nongnu.org; Mon, 27 Feb 2017 18:01:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ciUHs-00049H-36 for qemu-devel@nongnu.org; Mon, 27 Feb 2017 18:01:03 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50195) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ciUHr-00047j-OE for qemu-devel@nongnu.org; Mon, 27 Feb 2017 18:00:59 -0500 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v1RMraRo127332 for ; Mon, 27 Feb 2017 18:00:58 -0500 Received: from e06smtp15.uk.ibm.com (e06smtp15.uk.ibm.com [195.75.94.111]) by mx0a-001b2d01.pphosted.com with ESMTP id 28vknjbhgb-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 27 Feb 2017 18:00:58 -0500 Received: from localhost by e06smtp15.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Mon, 27 Feb 2017 23:00:53 -0000 Received: from b06cxnps3075.portsmouth.uk.ibm.com (d06relay10.portsmouth.uk.ibm.com [9.149.109.195]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id CC88B2190023; Mon, 27 Feb 2017 22:59:53 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v1RN0qaU54395110; Mon, 27 Feb 2017 23:00:52 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 47742AE056; Mon, 27 Feb 2017 21:58:42 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2B264AE04D; Mon, 27 Feb 2017 21:58:42 +0000 (GMT) Received: from smtp.lab.toulouse-stg.fr.ibm.com (unknown [9.101.4.1]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 27 Feb 2017 21:58:42 +0000 (GMT) Received: from bahia.lan (icon-9-164-183-34.megacenter.de.ibm.com [9.164.183.34]) by smtp.lab.toulouse-stg.fr.ibm.com (Postfix) with ESMTP id B7323220225; Tue, 28 Feb 2017 00:00:51 +0100 (CET) From: Greg Kurz To: qemu-devel@nongnu.org Date: Tue, 28 Feb 2017 00:00:15 +0100 X-Mailer: git-send-email 2.7.4 In-Reply-To: <1488236421-30983-1-git-send-email-groug@kaod.org> References: <1488236421-30983-1-git-send-email-groug@kaod.org> X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17022723-0020-0000-0000-000003100AE2 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17022723-0021-0000-0000-0000408CBE73 Message-Id: <1488236421-30983-26-git-send-email-groug@kaod.org> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2017-02-27_17:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=13 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1612050000 definitions=main-1702270213 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 148.163.156.1 Subject: [Qemu-devel] [PULL 25/31] 9pfs: local: chmod: don't follow symlinks X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , "Aneesh Kumar K.V" , Greg Kurz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" The local_chmod() callback is vulnerable to symlink attacks because it calls: (1) chmod() which follows symbolic links for all path elements (2) local_set_xattr()->setxattr() which follows symbolic links for all path elements (3) local_set_mapped_file_attr() which calls in turn local_fopen() and mkdir(), both functions following symbolic links for all path elements but the rightmost one We would need fchmodat() to implement AT_SYMLINK_NOFOLLOW to fix (1). This isn't the case on linux unfortunately: the kernel doesn't even have a flags argument to the syscall :-\ It is impossible to fix it in userspace in a race-free manner. This patch hence converts local_chmod() to rely on open_nofollow() and fchmod(). This fixes the vulnerability but introduces a limitation: the target file must readable and/or writable for the call to openat() to succeed. It introduces a local_set_xattrat() replacement to local_set_xattr() based on fsetxattrat() to fix (2), and a local_set_mapped_file_attrat() replacement to local_set_mapped_file_attr() based on local_fopenat() and mkdirat() to fix (3). No effort is made to factor out code because both local_set_xattr() and local_set_mapped_file_attr() will be dropped when all users have been converted to use the "at" versions. This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi --- hw/9pfs/9p-local.c | 178 +++++++++++++++++++++++++++++++++++++++++++++++++= ---- 1 file changed, 167 insertions(+), 11 deletions(-) diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c index 52b039625d1c..9a979a3b7c56 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -367,6 +367,155 @@ static int local_set_xattr(const char *path, FsCred *= credp) return 0; } =20 +static int local_set_mapped_file_attrat(int dirfd, const char *name, + FsCred *credp) +{ + FILE *fp; + int ret; + char buf[ATTR_MAX]; + int uid =3D -1, gid =3D -1, mode =3D -1, rdev =3D -1; + int map_dirfd; + + ret =3D mkdirat(dirfd, VIRTFS_META_DIR, 0700); + if (ret < 0 && errno !=3D EEXIST) { + return -1; + } + + map_dirfd =3D openat_dir(dirfd, VIRTFS_META_DIR); + if (map_dirfd =3D=3D -1) { + return -1; + } + + fp =3D local_fopenat(map_dirfd, name, "r"); + if (!fp) { + if (errno =3D=3D ENOENT) { + goto update_map_file; + } else { + close_preserve_errno(map_dirfd); + return -1; + } + } + memset(buf, 0, ATTR_MAX); + while (fgets(buf, ATTR_MAX, fp)) { + if (!strncmp(buf, "virtfs.uid", 10)) { + uid =3D atoi(buf + 11); + } else if (!strncmp(buf, "virtfs.gid", 10)) { + gid =3D atoi(buf + 11); + } else if (!strncmp(buf, "virtfs.mode", 11)) { + mode =3D atoi(buf + 12); + } else if (!strncmp(buf, "virtfs.rdev", 11)) { + rdev =3D atoi(buf + 12); + } + memset(buf, 0, ATTR_MAX); + } + fclose(fp); + +update_map_file: + fp =3D local_fopenat(map_dirfd, name, "w"); + close_preserve_errno(map_dirfd); + if (!fp) { + return -1; + } + + if (credp->fc_uid !=3D -1) { + uid =3D credp->fc_uid; + } + if (credp->fc_gid !=3D -1) { + gid =3D credp->fc_gid; + } + if (credp->fc_mode !=3D -1) { + mode =3D credp->fc_mode; + } + if (credp->fc_rdev !=3D -1) { + rdev =3D credp->fc_rdev; + } + + if (uid !=3D -1) { + fprintf(fp, "virtfs.uid=3D%d\n", uid); + } + if (gid !=3D -1) { + fprintf(fp, "virtfs.gid=3D%d\n", gid); + } + if (mode !=3D -1) { + fprintf(fp, "virtfs.mode=3D%d\n", mode); + } + if (rdev !=3D -1) { + fprintf(fp, "virtfs.rdev=3D%d\n", rdev); + } + fclose(fp); + + return 0; +} + +static int fchmodat_nofollow(int dirfd, const char *name, mode_t mode) +{ + int fd, ret; + + /* FIXME: this should be handled with fchmodat(AT_SYMLINK_NOFOLLOW). + * Unfortunately, the linux kernel doesn't implement it yet. As an + * alternative, let's open the file and use fchmod() instead. This + * may fail depending on the permissions of the file, but it is the + * best we can do to avoid TOCTTOU. We first try to open read-only + * in case name points to a directory. If that fails, we try write-only + * in case name doesn't point to a directory. + */ + fd =3D openat_file(dirfd, name, O_RDONLY, 0); + if (fd =3D=3D -1) { + /* In case the file is writable-only and isn't a directory. */ + if (errno =3D=3D EACCES) { + fd =3D openat_file(dirfd, name, O_WRONLY, 0); + } + if (fd =3D=3D -1 && errno =3D=3D EISDIR) { + errno =3D EACCES; + } + } + if (fd =3D=3D -1) { + return -1; + } + ret =3D fchmod(fd, mode); + close_preserve_errno(fd); + return ret; +} + +static int local_set_xattrat(int dirfd, const char *path, FsCred *credp) +{ + int err; + + if (credp->fc_uid !=3D -1) { + uint32_t tmp_uid =3D cpu_to_le32(credp->fc_uid); + err =3D fsetxattrat_nofollow(dirfd, path, "user.virtfs.uid", &tmp_= uid, + sizeof(uid_t), 0); + if (err) { + return err; + } + } + if (credp->fc_gid !=3D -1) { + uint32_t tmp_gid =3D cpu_to_le32(credp->fc_gid); + err =3D fsetxattrat_nofollow(dirfd, path, "user.virtfs.gid", &tmp_= gid, + sizeof(gid_t), 0); + if (err) { + return err; + } + } + if (credp->fc_mode !=3D -1) { + uint32_t tmp_mode =3D cpu_to_le32(credp->fc_mode); + err =3D fsetxattrat_nofollow(dirfd, path, "user.virtfs.mode", &tmp= _mode, + sizeof(mode_t), 0); + if (err) { + return err; + } + } + if (credp->fc_rdev !=3D -1) { + uint64_t tmp_rdev =3D cpu_to_le64(credp->fc_rdev); + err =3D fsetxattrat_nofollow(dirfd, path, "user.virtfs.rdev", &tmp= _rdev, + sizeof(dev_t), 0); + if (err) { + return err; + } + } + return 0; +} + static int local_post_create_passthrough(FsContext *fs_ctx, const char *pa= th, FsCred *credp) { @@ -558,22 +707,29 @@ static ssize_t local_pwritev(FsContext *ctx, V9fsFidO= penState *fs, =20 static int local_chmod(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp) { - char *buffer; + char *dirpath =3D g_path_get_dirname(fs_path->data); + char *name =3D g_path_get_basename(fs_path->data); int ret =3D -1; - char *path =3D fs_path->data; + int dirfd; + + dirfd =3D local_opendir_nofollow(fs_ctx, dirpath); + if (dirfd =3D=3D -1) { + goto out; + } =20 if (fs_ctx->export_flags & V9FS_SM_MAPPED) { - buffer =3D rpath(fs_ctx, path); - ret =3D local_set_xattr(buffer, credp); - g_free(buffer); + ret =3D local_set_xattrat(dirfd, name, credp); } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) { - return local_set_mapped_file_attr(fs_ctx, path, credp); - } else if ((fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) || - (fs_ctx->export_flags & V9FS_SM_NONE)) { - buffer =3D rpath(fs_ctx, path); - ret =3D chmod(buffer, credp->fc_mode); - g_free(buffer); + ret =3D local_set_mapped_file_attrat(dirfd, name, credp); + } else if (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH || + fs_ctx->export_flags & V9FS_SM_NONE) { + ret =3D fchmodat_nofollow(dirfd, name, credp->fc_mode); } + close_preserve_errno(dirfd); + +out: + g_free(dirpath); + g_free(name); return ret; } =20 --=20 2.7.4