From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0316DC43603 for ; Thu, 12 Dec 2019 17:20:01 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id C5D43205C9 for ; Thu, 12 Dec 2019 17:20:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EK+zpRg7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5D43205C9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:34560 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ifS87-000828-K6 for qemu-devel@archiver.kernel.org; Thu, 12 Dec 2019 12:19:59 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:51717) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ifRVq-00061C-S1 for qemu-devel@nongnu.org; Thu, 12 Dec 2019 11:40:28 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ifRVp-0002TV-Ih for qemu-devel@nongnu.org; Thu, 12 Dec 2019 11:40:26 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:41081 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 1ifRVp-0002So-DC for qemu-devel@nongnu.org; Thu, 12 Dec 2019 11:40:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1576168824; 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=YNzZKqJUsrE8SSGLz3sjbZqVFQobnUygsdjle8OWcRc=; b=EK+zpRg7jlea5eRCQ1E/JaRzswL/zdPhbZ4n6vr98RNvMvEkWbsfesJRVhW2XDMCWZpWxI TqpHYJ+pUnSghWRNYLL9frKAm/CCI63JW5oTnWnHssB9TDZe9S0ICP13dZSe2lA6XBGscJ mhuZ77kFPP63gLdqf34rY/VT2h2cE2Y= 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-76-oJvv-k8LOL-oIdbEh2wqQQ-1; Thu, 12 Dec 2019 11:40:23 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2860B189CD00 for ; Thu, 12 Dec 2019 16:40:22 +0000 (UTC) Received: from dgilbert-t580.localhost (ovpn-116-226.ams2.redhat.com [10.36.116.226]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4D21760BE1; Thu, 12 Dec 2019 16:40:21 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, stefanha@redhat.com, vgoyal@redhat.com Subject: [PATCH 047/104] virtiofsd: sandbox mount namespace Date: Thu, 12 Dec 2019 16:38:07 +0000 Message-Id: <20191212163904.159893-48-dgilbert@redhat.com> In-Reply-To: <20191212163904.159893-1-dgilbert@redhat.com> References: <20191212163904.159893-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: oJvv-k8LOL-oIdbEh2wqQQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable 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+qemu-devel=archiver.kernel.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 --- tools/virtiofsd/passthrough_ll.c | 89 ++++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough= _ll.c index 006908f25a..606824f002 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -49,6 +49,7 @@ #include #include #include +#include #include #include #include @@ -1925,6 +1926,58 @@ static void print_capabilities(void) printf("}\n"); } =20 +/* This magic is based on lxc's lxc_pivot_root() */ +static void setup_pivot_root(const char *source) +{ + int oldroot; + int newroot; + + oldroot =3D open("/", O_DIRECTORY | O_RDONLY | O_CLOEXEC); + if (oldroot < 0) { + fuse_log(FUSE_LOG_ERR, "open(/): %m\n"); + exit(1); + } + + newroot =3D 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 =3D open("/proc/self/fd", O_PATH); @@ -1934,6 +1987,39 @@ static void setup_proc_self_fd(struct lo_data *lo) } } =20 +/* + * Make the source directory our root so symlinks cannot escape and no oth= er + * files are accessible. + */ +static void setup_mount_namespace(const char *source) +{ + if (unshare(CLONE_NEWNS) !=3D 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, sou= rce); + exit(1); + } + + setup_pivot_root(source); +} + +/* + * Lock down this process to prevent access to other processes or files ou= tside + * 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 =3D FUSE_ARGS_INIT(argc, argv); @@ -2034,6 +2120,7 @@ int main(int argc, char *argv[]) } =20 lo.root.fd =3D open(lo.source, O_PATH); + if (lo.root.fd =3D=3D -1) { fuse_log(FUSE_LOG_ERR, "open(\"%s\", O_PATH): %m\n", lo.source); exit(1); @@ -2057,6 +2144,8 @@ int main(int argc, char *argv[]) /* Must be after daemonize to get the right /proc/self/fd */ setup_proc_self_fd(&lo); =20 + setup_sandbox(&lo); + /* Block until ctrl+c or fusermount -u */ ret =3D virtio_loop(se); =20 --=20 2.23.0