From patchwork Sun Feb 26 22:44:37 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kurz X-Patchwork-Id: 732649 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 3vWgjf59b8z9sDG for ; Mon, 27 Feb 2017 10:17:42 +1100 (AEDT) Received: from localhost ([::1]:48911 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ci84S-0008QG-5T for incoming@patchwork.ozlabs.org; Sun, 26 Feb 2017 18:17:40 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50968) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ci7Yg-00077f-7q for qemu-devel@nongnu.org; Sun, 26 Feb 2017 17:44:53 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ci7Yd-00037D-3a for qemu-devel@nongnu.org; Sun, 26 Feb 2017 17:44:50 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:53750 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 1ci7Yc-000372-T8 for qemu-devel@nongnu.org; Sun, 26 Feb 2017 17:44:47 -0500 Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v1QMi6bu104871 for ; Sun, 26 Feb 2017 17:44:46 -0500 Received: from e38.co.us.ibm.com (e38.co.us.ibm.com [32.97.110.159]) by mx0b-001b2d01.pphosted.com with ESMTP id 28u7d83302-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Sun, 26 Feb 2017 17:44:46 -0500 Received: from localhost by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Sun, 26 Feb 2017 15:44:41 -0700 Received: from b03cxnp08025.gho.boulder.ibm.com (b03cxnp08025.gho.boulder.ibm.com [9.17.130.17]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 038A61FF001E; Sun, 26 Feb 2017 15:44:18 -0700 (MST) Received: from b03ledav005.gho.boulder.ibm.com (b03ledav005.gho.boulder.ibm.com [9.17.130.236]) by b03cxnp08025.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v1QMie9h10224006; Sun, 26 Feb 2017 15:44:40 -0700 Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A25C1BE039; Sun, 26 Feb 2017 15:44:40 -0700 (MST) Received: from [192.168.66.23] (unknown [9.164.183.34]) by b03ledav005.gho.boulder.ibm.com (Postfix) with ESMTP id DB20EBE038; Sun, 26 Feb 2017 15:44:38 -0700 (MST) From: Greg Kurz To: qemu-devel@nongnu.org Date: Sun, 26 Feb 2017 23:44:37 +0100 In-Reply-To: <148814889214.28146.16915712763478774662.stgit@bahia> References: <148814889214.28146.16915712763478774662.stgit@bahia> User-Agent: StGit/0.17.1-20-gc0b1b-dirty MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17022622-0028-0000-0000-000007251CE2 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006689; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000204; SDB=6.00827425; UDB=6.00405424; IPR=6.00604941; BA=6.00005172; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00014449; XFM=3.00000011; UTC=2017-02-26 22:44:43 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17022622-0029-0000-0000-000033E4E47A Message-Id: <148814907731.28146.8856063692598979579.stgit@bahia> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2017-02-26_11:, , 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=8.0.1-1612050000 definitions=main-1702260234 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 v2 23/28] 9pfs: local: chown: 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: Jann Horn , Prasad J Pandit , Greg Kurz , "Aneesh Kumar K.V" , Stefan Hajnoczi Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" The local_chown() callback is vulnerable to symlink attacks because it calls: (1) lchown() which follows symbolic links for all path elements but the rightmost one (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 This patch converts local_chown() to rely on open_nofollow() and fchownat() to fix (1), as well as local_set_xattrat() and local_set_mapped_file_attrat() to fix (2) and (3) respectively. This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi --- hw/9pfs/9p-local.c | 26 +++++++++++++++++--------- 1 file changed, 17 insertions(+), 9 deletions(-) diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c index 72d219ec3d2b..0bacf722edfe 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -1160,23 +1160,31 @@ static int local_truncate(FsContext *ctx, V9fsPath *fs_path, off_t size) static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp) { - char *buffer; + char *dirpath = g_path_get_dirname(fs_path->data); + char *name = g_path_get_basename(fs_path->data); int ret = -1; - char *path = fs_path->data; + int dirfd; + + dirfd = local_opendir_nofollow(fs_ctx, dirpath); + if (dirfd == -1) { + goto out; + } if ((credp->fc_uid == -1 && credp->fc_gid == -1) || (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) || (fs_ctx->export_flags & V9FS_SM_NONE)) { - buffer = rpath(fs_ctx, path); - ret = lchown(buffer, credp->fc_uid, credp->fc_gid); - g_free(buffer); + ret = fchownat(dirfd, name, credp->fc_uid, credp->fc_gid, + AT_SYMLINK_NOFOLLOW); } else if (fs_ctx->export_flags & V9FS_SM_MAPPED) { - buffer = rpath(fs_ctx, path); - ret = local_set_xattr(buffer, credp); - g_free(buffer); + ret = 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); + ret = local_set_mapped_file_attrat(dirfd, name, credp); } + + close_preserve_errno(dirfd); +out: + g_free(name); + g_free(dirpath); return ret; }