From patchwork Mon Mar 20 23:07:34 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Roth X-Patchwork-Id: 741243 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 3vnBW90djsz9s7l for ; Tue, 21 Mar 2017 10:10:29 +1100 (AEDT) Received: from localhost ([::1]:35460 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cq6RV-0001SF-0C for incoming@patchwork.ozlabs.org; Mon, 20 Mar 2017 19:10:25 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40307) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cq6QU-0001Qo-9v for qemu-devel@nongnu.org; Mon, 20 Mar 2017 19:09:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cq6QR-0004fd-2p for qemu-devel@nongnu.org; Mon, 20 Mar 2017 19:09:22 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:41224) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cq6QQ-0004ew-Q9 for qemu-devel@nongnu.org; Mon, 20 Mar 2017 19:09:19 -0400 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v2KN8Xg1128055 for ; Mon, 20 Mar 2017 19:09:17 -0400 Received: from e37.co.us.ibm.com (e37.co.us.ibm.com [32.97.110.158]) by mx0a-001b2d01.pphosted.com with ESMTP id 29ambn28yc-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 20 Mar 2017 19:09:17 -0400 Received: from localhost by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Mon, 20 Mar 2017 17:09:13 -0600 Received: from b03ledav005.gho.boulder.ibm.com (b03ledav005.gho.boulder.ibm.com [9.17.130.236]) by b03cxnp08028.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v2KN9DCl15270286; Mon, 20 Mar 2017 16:09:13 -0700 Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 02193BE03B; Mon, 20 Mar 2017 17:09:13 -0600 (MDT) Received: from localhost (unknown [9.53.92.194]) by b03ledav005.gho.boulder.ibm.com (Postfix) with ESMTP id C44C3BE038; Mon, 20 Mar 2017 17:09:12 -0600 (MDT) From: Michael Roth To: qemu-devel@nongnu.org Date: Mon, 20 Mar 2017 18:07:34 -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: 17032023-0024-0000-0000-00001617D56D 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=6.00411161; 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 23:09:14 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17032023-0025-0000-0000-0000499B6D45 Message-Id: <1490051325-3770-11-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: 148.163.156.1 Subject: [Qemu-devel] [PATCH 10/81] 9pfs: local: lremovexattr: 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_lremovexattr() callback is vulnerable to symlink attacks because it calls lremovexattr() which follows symbolic links in all path elements but the rightmost one. This patch introduces a helper to emulate the non-existing fremovexattrat() function: it is implemented with /proc/self/fd which provides a trusted path that can be safely passed to lremovexattr(). local_lremovexattr() is converted to use this helper and opendir_nofollow(). This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi (cherry picked from commit 72f0d0bf51362011c4d841a89fb8f5cfb16e0bf3) Signed-off-by: Greg Kurz Signed-off-by: Michael Roth --- hw/9pfs/9p-posix-acl.c | 10 ++-------- hw/9pfs/9p-xattr-user.c | 8 +------- hw/9pfs/9p-xattr.c | 36 +++++++++++++++++++++++++++++++----- hw/9pfs/9p-xattr.h | 2 ++ 4 files changed, 36 insertions(+), 20 deletions(-) diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c index 0154e2a..bbf8906 100644 --- a/hw/9pfs/9p-posix-acl.c +++ b/hw/9pfs/9p-posix-acl.c @@ -58,10 +58,8 @@ static int mp_pacl_removexattr(FsContext *ctx, const char *path, const char *name) { int ret; - char *buffer; - buffer = rpath(ctx, path); - ret = lremovexattr(buffer, MAP_ACL_ACCESS); + ret = local_removexattr_nofollow(ctx, path, MAP_ACL_ACCESS); if (ret == -1 && errno == ENODATA) { /* * We don't get ENODATA error when trying to remove a @@ -71,7 +69,6 @@ static int mp_pacl_removexattr(FsContext *ctx, errno = 0; ret = 0; } - g_free(buffer); return ret; } @@ -111,10 +108,8 @@ static int mp_dacl_removexattr(FsContext *ctx, const char *path, const char *name) { int ret; - char *buffer; - buffer = rpath(ctx, path); - ret = lremovexattr(buffer, MAP_ACL_DEFAULT); + ret = local_removexattr_nofollow(ctx, path, MAP_ACL_DEFAULT); if (ret == -1 && errno == ENODATA) { /* * We don't get ENODATA error when trying to remove a @@ -124,7 +119,6 @@ static int mp_dacl_removexattr(FsContext *ctx, errno = 0; ret = 0; } - g_free(buffer); return ret; } diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c index 1840a5d..2c90817 100644 --- a/hw/9pfs/9p-xattr-user.c +++ b/hw/9pfs/9p-xattr-user.c @@ -81,9 +81,6 @@ static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name, static int mp_user_removexattr(FsContext *ctx, const char *path, const char *name) { - char *buffer; - int ret; - if (strncmp(name, "user.virtfs.", 12) == 0) { /* * Don't allow fetch of user.virtfs namesapce @@ -92,10 +89,7 @@ static int mp_user_removexattr(FsContext *ctx, errno = EACCES; return -1; } - buffer = rpath(ctx, path); - ret = lremovexattr(buffer, name); - g_free(buffer); - return ret; + return local_removexattr_nofollow(ctx, path, name); } XattrOperations mapped_user_xattr = { diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c index a0167dd..eec160b 100644 --- a/hw/9pfs/9p-xattr.c +++ b/hw/9pfs/9p-xattr.c @@ -234,17 +234,43 @@ int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value, return local_setxattr_nofollow(ctx, path, name, value, size, flags); } -int pt_removexattr(FsContext *ctx, const char *path, const char *name) +static ssize_t fremovexattrat_nofollow(int dirfd, const char *filename, + const char *name) { - char *buffer; + char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename); int ret; - buffer = rpath(ctx, path); - ret = lremovexattr(path, name); - g_free(buffer); + ret = lremovexattr(proc_path, name); + g_free(proc_path); return ret; } +ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path, + const char *name) +{ + char *dirpath = g_path_get_dirname(path); + char *filename = g_path_get_basename(path); + int dirfd; + ssize_t ret = -1; + + dirfd = local_opendir_nofollow(ctx, dirpath); + if (dirfd == -1) { + goto out; + } + + ret = fremovexattrat_nofollow(dirfd, filename, name); + close_preserve_errno(dirfd); +out: + g_free(dirpath); + g_free(filename); + return ret; +} + +int pt_removexattr(FsContext *ctx, const char *path, const char *name) +{ + return local_removexattr_nofollow(ctx, path, name); +} + ssize_t notsup_getxattr(FsContext *ctx, const char *path, const char *name, void *value, size_t size) { diff --git a/hw/9pfs/9p-xattr.h b/hw/9pfs/9p-xattr.h index 7558970..0d83996 100644 --- a/hw/9pfs/9p-xattr.h +++ b/hw/9pfs/9p-xattr.h @@ -34,6 +34,8 @@ ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path, ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path, const char *name, void *value, size_t size, int flags); +ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path, + const char *name); extern XattrOperations mapped_user_xattr; extern XattrOperations passthrough_user_xattr;