From patchwork Sun Feb 26 22:42:26 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kurz X-Patchwork-Id: 732628 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 3vWg3p51G4z9s9Y for ; Mon, 27 Feb 2017 09:48:22 +1100 (AEDT) Received: from localhost ([::1]:48765 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ci7c4-0001k4-53 for incoming@patchwork.ozlabs.org; Sun, 26 Feb 2017 17:48:20 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50489) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ci7WX-0004tz-L0 for qemu-devel@nongnu.org; Sun, 26 Feb 2017 17:42:40 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ci7WU-0002oZ-Hp for qemu-devel@nongnu.org; Sun, 26 Feb 2017 17:42:37 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:53028) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ci7WU-0002oN-7I for qemu-devel@nongnu.org; Sun, 26 Feb 2017 17:42:34 -0500 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v1QMcQ9v074879 for ; Sun, 26 Feb 2017 17:42:33 -0500 Received: from e31.co.us.ibm.com (e31.co.us.ibm.com [32.97.110.149]) by mx0a-001b2d01.pphosted.com with ESMTP id 28u6asvx8u-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Sun, 26 Feb 2017 17:42:32 -0500 Received: from localhost by e31.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Sun, 26 Feb 2017 15:42:30 -0700 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id F081619D801C; Sun, 26 Feb 2017 15:41:40 -0700 (MST) Received: from b03ledav001.gho.boulder.ibm.com (b03ledav001.gho.boulder.ibm.com [9.17.130.232]) by b03cxnp08027.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v1QMgT2510813700; Sun, 26 Feb 2017 15:42:29 -0700 Received: from b03ledav001.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5D88E6E038; Sun, 26 Feb 2017 15:42:29 -0700 (MST) Received: from [192.168.66.23] (unknown [9.164.183.34]) by b03ledav001.gho.boulder.ibm.com (Postfix) with ESMTP id AAE366E035; Sun, 26 Feb 2017 15:42:27 -0700 (MST) From: Greg Kurz To: qemu-devel@nongnu.org Date: Sun, 26 Feb 2017 23:42:26 +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: 17022622-8235-0000-0000-00000B0E4156 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006689; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000204; SDB=6.00827424; UDB=6.00405424; IPR=6.00604940; 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 22:42:32 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17022622-8236-0000-0000-000039EBE2DF Message-Id: <148814894608.28146.6510271749788030194.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-1702260233 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 v2 07/28] 9pfs: local: lgetxattr: 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_lgetxattr() callback is vulnerable to symlink attacks because it calls lgetxattr() which follows symbolic links in all path elements but the rightmost one. This patch introduces a helper to emulate the non-existing fgetxattrat() function: it is implemented with /proc/self/fd which provides a trusted path that can be safely passed to lgetxattr(). local_lgetxattr() is converted to use this helper and opendir_nofollow(). This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi --- v2: - introduce /proc based fgetxattrat_nofollow() --- hw/9pfs/9p-posix-acl.c | 16 ++-------------- hw/9pfs/9p-util.c | 12 ++++++++++++ hw/9pfs/9p-util.h | 2 ++ hw/9pfs/9p-xattr-user.c | 8 +------- hw/9pfs/9p-xattr.c | 31 ++++++++++++++++++++++++------- hw/9pfs/9p-xattr.h | 2 ++ 6 files changed, 43 insertions(+), 28 deletions(-) diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c index ec003181cd33..9435e27a368c 100644 --- a/hw/9pfs/9p-posix-acl.c +++ b/hw/9pfs/9p-posix-acl.c @@ -25,13 +25,7 @@ static ssize_t mp_pacl_getxattr(FsContext *ctx, const char *path, const char *name, void *value, size_t size) { - char *buffer; - ssize_t ret; - - buffer = rpath(ctx, path); - ret = lgetxattr(buffer, MAP_ACL_ACCESS, value, size); - g_free(buffer); - return ret; + return local_getxattr_nofollow(ctx, path, MAP_ACL_ACCESS, value, size); } static ssize_t mp_pacl_listxattr(FsContext *ctx, const char *path, @@ -89,13 +83,7 @@ static int mp_pacl_removexattr(FsContext *ctx, static ssize_t mp_dacl_getxattr(FsContext *ctx, const char *path, const char *name, void *value, size_t size) { - char *buffer; - ssize_t ret; - - buffer = rpath(ctx, path); - ret = lgetxattr(buffer, MAP_ACL_DEFAULT, value, size); - g_free(buffer); - return ret; + return local_getxattr_nofollow(ctx, path, MAP_ACL_DEFAULT, value, size); } static ssize_t mp_dacl_listxattr(FsContext *ctx, const char *path, diff --git a/hw/9pfs/9p-util.c b/hw/9pfs/9p-util.c index 62fd7a76212a..b3dd1f160280 100644 --- a/hw/9pfs/9p-util.c +++ b/hw/9pfs/9p-util.c @@ -11,6 +11,7 @@ */ #include "qemu/osdep.h" +#include "qemu/xattr.h" #include "9p-util.h" int openat_nofollow(int dirfd, const char *path, int flags, mode_t mode) @@ -51,3 +52,14 @@ int openat_nofollow(int dirfd, const char *path, int flags, mode_t mode) return fd; } + +ssize_t fgetxattrat_nofollow(int dirfd, const char *filename, const char *name, + void *value, size_t size) +{ + char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename); + int ret; + + ret = lgetxattr(proc_path, name, value, size); + g_free(proc_path); + return ret; +} diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h index ca0d440ddc1e..5a1be712130e 100644 --- a/hw/9pfs/9p-util.h +++ b/hw/9pfs/9p-util.h @@ -44,5 +44,7 @@ static inline int openat_file(int dirfd, const char *name, int flags, } int openat_nofollow(int dirfd, const char *path, int flags, mode_t mode); +ssize_t fgetxattrat_nofollow(int dirfd, const char *path, const char *name, + void *value, size_t size); #endif diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c index f87530c8b526..4071fbc4c086 100644 --- a/hw/9pfs/9p-xattr-user.c +++ b/hw/9pfs/9p-xattr-user.c @@ -20,9 +20,6 @@ static ssize_t mp_user_getxattr(FsContext *ctx, const char *path, const char *name, void *value, size_t size) { - char *buffer; - ssize_t ret; - if (strncmp(name, "user.virtfs.", 12) == 0) { /* * Don't allow fetch of user.virtfs namesapce @@ -31,10 +28,7 @@ static ssize_t mp_user_getxattr(FsContext *ctx, const char *path, errno = ENOATTR; return -1; } - buffer = rpath(ctx, path); - ret = lgetxattr(buffer, name, value, size); - g_free(buffer); - return ret; + return local_getxattr_nofollow(ctx, path, name, value, size); } static ssize_t mp_user_listxattr(FsContext *ctx, const char *path, diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c index 19a2daf02f5c..aa4391e6b317 100644 --- a/hw/9pfs/9p-xattr.c +++ b/hw/9pfs/9p-xattr.c @@ -15,6 +15,8 @@ #include "9p.h" #include "fsdev/file-op-9p.h" #include "9p-xattr.h" +#include "9p-util.h" +#include "9p-local.h" static XattrOperations *get_xattr_operations(XattrOperations **h, @@ -143,18 +145,33 @@ int v9fs_remove_xattr(FsContext *ctx, } -ssize_t pt_getxattr(FsContext *ctx, const char *path, const char *name, - void *value, size_t size) +ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path, + const char *name, void *value, size_t size) { - char *buffer; - ssize_t ret; + 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; + } - buffer = rpath(ctx, path); - ret = lgetxattr(buffer, name, value, size); - g_free(buffer); + ret = fgetxattrat_nofollow(dirfd, filename, name, value, size); + close_preserve_errno(dirfd); +out: + g_free(dirpath); + g_free(filename); return ret; } +ssize_t pt_getxattr(FsContext *ctx, const char *path, const char *name, + void *value, size_t size) +{ + return local_getxattr_nofollow(ctx, path, name, value, size); +} + int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value, size_t size, int flags) { diff --git a/hw/9pfs/9p-xattr.h b/hw/9pfs/9p-xattr.h index 3f43f5153f3c..69a8b6b62e3c 100644 --- a/hw/9pfs/9p-xattr.h +++ b/hw/9pfs/9p-xattr.h @@ -29,6 +29,8 @@ typedef struct xattr_operations const char *path, const char *name); } XattrOperations; +ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path, + const char *name, void *value, size_t size); extern XattrOperations mapped_user_xattr; extern XattrOperations passthrough_user_xattr;