From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37606) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cif3h-0001E6-2v for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:31:08 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cif3d-0007xX-Mo for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:31:05 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:53559 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 1cif3d-0007xE-Du for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:31:01 -0500 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v1SASkNb043957 for ; Tue, 28 Feb 2017 05:31:00 -0500 Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) by mx0b-001b2d01.pphosted.com with ESMTP id 28vn6ar6fq-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 28 Feb 2017 05:31:00 -0500 Received: from localhost by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 28 Feb 2017 10:30:58 -0000 From: Greg Kurz Date: Tue, 28 Feb 2017 11:30:20 +0100 In-Reply-To: <1488277840-18608-1-git-send-email-groug@kaod.org> References: <1488277840-18608-1-git-send-email-groug@kaod.org> Message-Id: <1488277840-18608-9-git-send-email-groug@kaod.org> Subject: [Qemu-devel] [PULL 08/28] 9pfs: local: llistxattr: don't follow symlinks List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Peter Maydell , "Aneesh Kumar K.V" , Greg Kurz The local_llistxattr() callback is vulnerable to symlink attacks because it calls llistxattr() which follows symbolic links in all path elements but the rightmost one. This patch introduces a helper to emulate the non-existing flistxattrat() function: it is implemented with /proc/self/fd which provides a trusted path that can be safely passed to llistxattr(). local_llistxattr() is converted to use this helper and opendir_nofollow(). This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi --- hw/9pfs/9p-xattr.c | 35 +++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-) diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c index aa4391e6b317..54193c630c9d 100644 --- a/hw/9pfs/9p-xattr.c +++ b/hw/9pfs/9p-xattr.c @@ -60,6 +60,16 @@ ssize_t pt_listxattr(FsContext *ctx, const char *path, return name_size; } +static ssize_t flistxattrat_nofollow(int dirfd, const char *filename, + char *list, size_t size) +{ + char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename); + int ret; + + ret = llistxattr(proc_path, list, size); + g_free(proc_path); + return ret; +} /* * Get the list and pass to each layer to find out whether @@ -69,24 +79,37 @@ ssize_t v9fs_list_xattr(FsContext *ctx, const char *path, void *value, size_t vsize) { ssize_t size = 0; - char *buffer; void *ovalue = value; XattrOperations *xops; char *orig_value, *orig_value_start; ssize_t xattr_len, parsed_len = 0, attr_len; + char *dirpath, *name; + int dirfd; /* Get the actual len */ - buffer = rpath(ctx, path); - xattr_len = llistxattr(buffer, value, 0); + dirpath = g_path_get_dirname(path); + dirfd = local_opendir_nofollow(ctx, dirpath); + g_free(dirpath); + if (dirfd == -1) { + return -1; + } + + name = g_path_get_basename(path); + xattr_len = flistxattrat_nofollow(dirfd, name, value, 0); if (xattr_len <= 0) { - g_free(buffer); + g_free(name); + close_preserve_errno(dirfd); return xattr_len; } /* Now fetch the xattr and find the actual size */ orig_value = g_malloc(xattr_len); - xattr_len = llistxattr(buffer, orig_value, xattr_len); - g_free(buffer); + xattr_len = flistxattrat_nofollow(dirfd, name, orig_value, xattr_len); + g_free(name); + close_preserve_errno(dirfd); + if (xattr_len < 0) { + return -1; + } /* store the orig pointer */ orig_value_start = orig_value; -- 2.7.4