From patchwork Mon Mar 20 23:07:41 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Roth X-Patchwork-Id: 741260 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3vnBnr2dmnz9s06 for ; Tue, 21 Mar 2017 10:23:12 +1100 (AEDT) Received: from localhost ([::1]:35545 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cq6dp-0004E8-Mo for incoming@patchwork.ozlabs.org; Mon, 20 Mar 2017 19:23:09 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40332) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cq6QW-0001Qs-DG for qemu-devel@nongnu.org; Mon, 20 Mar 2017 19:09:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cq6QR-0004gQ-P4 for qemu-devel@nongnu.org; Mon, 20 Mar 2017 19:09:23 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:39508 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cq6QR-0004fh-Iq for qemu-devel@nongnu.org; Mon, 20 Mar 2017 19:09:19 -0400 Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v2KN8a7v119417 for ; Mon, 20 Mar 2017 19:09:19 -0400 Received: from e16.ny.us.ibm.com (e16.ny.us.ibm.com [129.33.205.206]) by mx0b-001b2d01.pphosted.com with ESMTP id 29ajfe8ngc-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 20 Mar 2017 19:09:18 -0400 Received: from localhost by e16.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Mon, 20 Mar 2017 19:09:17 -0400 Received: from b01ledav002.gho.pok.ibm.com (b01ledav002.gho.pok.ibm.com [9.57.199.107]) by b01cxnp22035.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v2KN9GJF61145098; Mon, 20 Mar 2017 23:09:16 GMT Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A1A1E124044; Mon, 20 Mar 2017 19:09:12 -0400 (EDT) Received: from localhost (unknown [9.53.92.194]) by b01ledav002.gho.pok.ibm.com (Postfix) with ESMTP id 8658A12403F; Mon, 20 Mar 2017 19:09:12 -0400 (EDT) From: Michael Roth To: qemu-devel@nongnu.org Date: Mon, 20 Mar 2017 18:07:41 -0500 X-Mailer: git-send-email 2.7.4 In-Reply-To: <1490051325-3770-1-git-send-email-mdroth@linux.vnet.ibm.com> References: <1490051325-3770-1-git-send-email-mdroth@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17032023-0024-0000-0000-0000021F8DCE X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006819; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000206; SDB=6.00836553; UDB=6.00411162; IPR=6.00614321; BA=6.00005224; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00014732; XFM=3.00000013; UTC=2017-03-20 23:09:18 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17032023-0025-0000-0000-000042B6B6CF Message-Id: <1490051325-3770-18-git-send-email-mdroth@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2017-03-20_16:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=3 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1703200196 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 148.163.158.5 Subject: [Qemu-devel] [PATCH 17/81] 9pfs: local: lstat: 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: Greg Kurz , qemu-stable@nongnu.org, Greg Kurz Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" From: Greg Kurz The local_lstat() callback is vulnerable to symlink attacks because it calls: (1) lstat() which follows symbolic links in all path elements but the rightmost one (2) getxattr() which follows symbolic links in all path elements (3) local_mapped_file_attr()->local_fopen()->openat(O_NOFOLLOW) which follows symbolic links in all path elements but the rightmost one This patch converts local_lstat() to rely on opendir_nofollow() and fstatat(AT_SYMLINK_NOFOLLOW) to fix (1), fgetxattrat_nofollow() to fix (2). A new local_fopenat() helper is introduced as a replacement to local_fopen() to fix (3). No effort is made to factor out code because local_fopen() will be dropped when all users have been converted to call local_fopenat(). This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi (cherry picked from commit f9aef99b3e6df88036436b0d3dc3d504b9346c8c) Signed-off-by: Greg Kurz Signed-off-by: Michael Roth --- hw/9pfs/9p-local.c | 78 ++++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 61 insertions(+), 17 deletions(-) diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c index c290b6c..547baa4 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -111,17 +111,49 @@ static FILE *local_fopen(const char *path, const char *mode) return fp; } +static FILE *local_fopenat(int dirfd, const char *name, const char *mode) +{ + int fd, o_mode = 0; + FILE *fp; + int flags; + /* + * only supports two modes + */ + if (mode[0] == 'r') { + flags = O_RDONLY; + } else if (mode[0] == 'w') { + flags = O_WRONLY | O_TRUNC | O_CREAT; + o_mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; + } else { + return NULL; + } + fd = openat_file(dirfd, name, flags, o_mode); + if (fd == -1) { + return NULL; + } + fp = fdopen(fd, mode); + if (!fp) { + close(fd); + } + return fp; +} + #define ATTR_MAX 100 -static void local_mapped_file_attr(FsContext *ctx, const char *path, +static void local_mapped_file_attr(int dirfd, const char *name, struct stat *stbuf) { FILE *fp; char buf[ATTR_MAX]; - char *attr_path; + int map_dirfd; - attr_path = local_mapped_attr_path(ctx, path); - fp = local_fopen(attr_path, "r"); - g_free(attr_path); + map_dirfd = openat(dirfd, VIRTFS_META_DIR, + O_RDONLY | O_DIRECTORY | O_NOFOLLOW); + if (map_dirfd == -1) { + return; + } + + fp = local_fopenat(map_dirfd, name, "r"); + close_preserve_errno(map_dirfd); if (!fp) { return; } @@ -143,12 +175,17 @@ static void local_mapped_file_attr(FsContext *ctx, const char *path, static int local_lstat(FsContext *fs_ctx, V9fsPath *fs_path, struct stat *stbuf) { - int err; - char *buffer; - char *path = fs_path->data; + int err = -1; + char *dirpath = g_path_get_dirname(fs_path->data); + char *name = g_path_get_basename(fs_path->data); + int dirfd; - buffer = rpath(fs_ctx, path); - err = lstat(buffer, stbuf); + dirfd = local_opendir_nofollow(fs_ctx, dirpath); + if (dirfd == -1) { + goto out; + } + + err = fstatat(dirfd, name, stbuf, AT_SYMLINK_NOFOLLOW); if (err) { goto err_out; } @@ -158,25 +195,32 @@ static int local_lstat(FsContext *fs_ctx, V9fsPath *fs_path, struct stat *stbuf) gid_t tmp_gid; mode_t tmp_mode; dev_t tmp_dev; - if (getxattr(buffer, "user.virtfs.uid", &tmp_uid, sizeof(uid_t)) > 0) { + + if (fgetxattrat_nofollow(dirfd, name, "user.virtfs.uid", &tmp_uid, + sizeof(uid_t)) > 0) { stbuf->st_uid = le32_to_cpu(tmp_uid); } - if (getxattr(buffer, "user.virtfs.gid", &tmp_gid, sizeof(gid_t)) > 0) { + if (fgetxattrat_nofollow(dirfd, name, "user.virtfs.gid", &tmp_gid, + sizeof(gid_t)) > 0) { stbuf->st_gid = le32_to_cpu(tmp_gid); } - if (getxattr(buffer, "user.virtfs.mode", - &tmp_mode, sizeof(mode_t)) > 0) { + if (fgetxattrat_nofollow(dirfd, name, "user.virtfs.mode", &tmp_mode, + sizeof(mode_t)) > 0) { stbuf->st_mode = le32_to_cpu(tmp_mode); } - if (getxattr(buffer, "user.virtfs.rdev", &tmp_dev, sizeof(dev_t)) > 0) { + if (fgetxattrat_nofollow(dirfd, name, "user.virtfs.rdev", &tmp_dev, + sizeof(dev_t)) > 0) { stbuf->st_rdev = le64_to_cpu(tmp_dev); } } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) { - local_mapped_file_attr(fs_ctx, path, stbuf); + local_mapped_file_attr(dirfd, name, stbuf); } err_out: - g_free(buffer); + close_preserve_errno(dirfd); +out: + g_free(name); + g_free(dirpath); return err; }