From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37694) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cif3m-0001JH-LQ for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:31:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cif3l-000808-KC for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:31:10 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:53568) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cif3l-0007zd-5h for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:31:09 -0500 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 v1SATZlk137632 for ; Tue, 28 Feb 2017 05:31:07 -0500 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 28vm1wv6ct-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 28 Feb 2017 05:31:07 -0500 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 28 Feb 2017 10:31:05 -0000 From: Greg Kurz Date: Tue, 28 Feb 2017 11:30:28 +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: <1488277840-18608-17-git-send-email-groug@kaod.org> Subject: [Qemu-devel] [PULL 16/28] 9pfs: local: readlink: 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_readlink() callback is vulnerable to symlink attacks because it calls: (1) open(O_NOFOLLOW) which follows symbolic links for all path elements but the rightmost one (2) readlink() which follows symbolic links for all path elements but the rightmost one This patch converts local_readlink() to rely on open_nofollow() to fix (1) and opendir_nofollow(), readlinkat() to fix (2). 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 1a3dfd774012..e373cca3b78d 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -340,27 +340,35 @@ static ssize_t local_readlink(FsContext *fs_ctx, V9fsPath *fs_path, char *buf, size_t bufsz) { ssize_t tsize = -1; - char *buffer; - char *path = fs_path->data; if ((fs_ctx->export_flags & V9FS_SM_MAPPED) || (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE)) { int fd; - buffer = rpath(fs_ctx, path); - fd = open(buffer, O_RDONLY | O_NOFOLLOW); - g_free(buffer); + + fd = local_open_nofollow(fs_ctx, fs_path->data, O_RDONLY, 0); if (fd == -1) { return -1; } do { tsize = read(fd, (void *)buf, bufsz); } while (tsize == -1 && errno == EINTR); - close(fd); + close_preserve_errno(fd); } else if ((fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) || (fs_ctx->export_flags & V9FS_SM_NONE)) { - buffer = rpath(fs_ctx, path); - tsize = readlink(buffer, buf, bufsz); - g_free(buffer); + char *dirpath = g_path_get_dirname(fs_path->data); + char *name = g_path_get_basename(fs_path->data); + int dirfd; + + dirfd = local_opendir_nofollow(fs_ctx, dirpath); + if (dirfd == -1) { + goto out; + } + + tsize = readlinkat(dirfd, name, buf, bufsz); + close_preserve_errno(dirfd); + out: + g_free(name); + g_free(dirpath); } return tsize; } -- 2.7.4