From patchwork Thu Oct 24 11:27:09 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Dr. David Alan Gilbert" X-Patchwork-Id: 1182971 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.b="NIibLvZ0"; dkim-atps=neutral Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 46zQj9583lz9sQv for ; Thu, 24 Oct 2019 22:57:33 +1100 (AEDT) Received: from localhost ([::1]:40400 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNbk9-0005d9-QU for incoming@patchwork.ozlabs.org; Thu, 24 Oct 2019 07:57:29 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39433) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNbIF-0003p5-Bv for qemu-devel@nongnu.org; Thu, 24 Oct 2019 07:28:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iNbID-00007J-BY for qemu-devel@nongnu.org; Thu, 24 Oct 2019 07:28:39 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:30773 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iNbID-00006W-7L for qemu-devel@nongnu.org; Thu, 24 Oct 2019 07:28:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1571916515; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ybIvLXARifCanoTHks1af93zgXi2Fkq9toNkp0Uvdtk=; b=NIibLvZ0sbnyhuScirC4qzmybPXDY5qaPfO3ZREG2vkS6o2YTiqUzqZS1/fNwOpkod9mhK j7HdbtbTfHMqFZV8seYPO1Zd8xKj1ubu7iXt5IyguHqxJ1Jjd7G/llOJN3fwDUVcgbYrY5 sMWg8Xbh9IBhOrtmx/0Ic0Zjlx8iiIo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-374-uJu0xQ7sN7mrcQGA0fkjGw-1; Thu, 24 Oct 2019 07:28:31 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0EBA1107AD31; Thu, 24 Oct 2019 11:28:30 +0000 (UTC) Received: from dgilbert-t580.localhost (ovpn-117-248.ams2.redhat.com [10.36.117.248]) by smtp.corp.redhat.com (Postfix) with ESMTP id 53A1F196B2; Thu, 24 Oct 2019 11:28:27 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, renzhen@linux.alibaba.com, eguan@linux.alibaba.com, ganesh.mahalingam@intel.com, m.mizuma@jp.fujitsu.com, mszeredi@redhat.com, misono.tomohiro@jp.fujitsu.com, tao.peng@linux.alibaba.com, piaojun@huawei.com, stefanha@redhat.com, vgoyal@redhat.com, mst@redhat.com, berrange@redhat.com Subject: [PATCH 16/25] virtiofsd: sandbox mount namespace Date: Thu, 24 Oct 2019 12:27:09 +0100 Message-Id: <20191024112718.34657-17-dgilbert@redhat.com> In-Reply-To: <20191024112718.34657-1-dgilbert@redhat.com> References: <20191024112718.34657-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: uJu0xQ7sN7mrcQGA0fkjGw-1 X-Mimecast-Spam-Score: 0 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" From: Stefan Hajnoczi Use a mount namespace with the shared directory tree mounted at "/" and no other mounts. This prevents symlink escape attacks because symlink targets are resolved only against the shared directory and cannot go outside it. Signed-off-by: Stefan Hajnoczi Signed-off-by: Peng Tao --- contrib/virtiofsd/passthrough_ll.c | 89 ++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c index 3ddf22d162..20a34d4d83 100644 --- a/contrib/virtiofsd/passthrough_ll.c +++ b/contrib/virtiofsd/passthrough_ll.c @@ -51,6 +51,7 @@ #include #include #include +#include #include "passthrough_helpers.h" @@ -1821,6 +1822,58 @@ static void print_capabilities(void) printf("}\n"); } +/* This magic is based on lxc's lxc_pivot_root() */ +static void setup_pivot_root(const char *source) +{ + int oldroot; + int newroot; + + oldroot = open("/", O_DIRECTORY | O_RDONLY | O_CLOEXEC); + if (oldroot < 0) { + fuse_log(FUSE_LOG_ERR, "open(/): %m\n"); + exit(1); + } + + newroot = open(source, O_DIRECTORY | O_RDONLY | O_CLOEXEC); + if (newroot < 0) { + fuse_log(FUSE_LOG_ERR, "open(%s): %m\n", source); + exit(1); + } + + if (fchdir(newroot) < 0) { + fuse_log(FUSE_LOG_ERR, "fchdir(newroot): %m\n"); + exit(1); + } + + if (syscall(__NR_pivot_root, ".", ".") < 0){ + fuse_log(FUSE_LOG_ERR, "pivot_root(., .): %m\n"); + exit(1); + } + + if (fchdir(oldroot) < 0) { + fuse_log(FUSE_LOG_ERR, "fchdir(oldroot): %m\n"); + exit(1); + } + + if (mount("", ".", "", MS_SLAVE | MS_REC, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(., MS_SLAVE | MS_REC): %m\n"); + exit(1); + } + + if (umount2(".", MNT_DETACH) < 0) { + fuse_log(FUSE_LOG_ERR, "umount2(., MNT_DETACH): %m\n"); + exit(1); + } + + if (fchdir(newroot) < 0) { + fuse_log(FUSE_LOG_ERR, "fchdir(newroot): %m\n"); + exit(1); + } + + close(newroot); + close(oldroot); +} + static void setup_proc_self_fd(struct lo_data *lo) { lo->proc_self_fd = open("/proc/self/fd", O_PATH); @@ -1830,6 +1883,39 @@ static void setup_proc_self_fd(struct lo_data *lo) } } +/* + * Make the source directory our root so symlinks cannot escape and no other + * files are accessible. + */ +static void setup_mount_namespace(const char *source) +{ + if (unshare(CLONE_NEWNS) != 0) { + fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWNS): %m\n"); + exit(1); + } + + if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_PRIVATE): %m\n"); + exit(1); + } + + if (mount(source, source, NULL, MS_BIND, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(%s, %s, MS_BIND): %m\n", source, source); + exit(1); + } + + setup_pivot_root(source); +} + +/* + * Lock down this process to prevent access to other processes or files outside + * source directory. This reduces the impact of arbitrary code execution bugs. + */ +static void setup_sandbox(struct lo_data *lo) +{ + setup_mount_namespace(lo->source); +} + int main(int argc, char *argv[]) { struct fuse_args args = FUSE_ARGS_INIT(argc, argv); @@ -1927,6 +2013,7 @@ int main(int argc, char *argv[]) } lo.root.fd = open(lo.source, O_PATH); + if (lo.root.fd == -1) { fuse_log(FUSE_LOG_ERR, "open(\"%s\", O_PATH): %m\n", lo.source); @@ -1948,6 +2035,8 @@ int main(int argc, char *argv[]) /* Must be after daemonize to get the right /proc/self/fd */ setup_proc_self_fd(&lo); + setup_sandbox(&lo); + /* Block until ctrl+c or fusermount -u */ ret = virtio_loop(se);