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 5B9BFC2D0DB for ; Thu, 23 Jan 2020 19:51:36 +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 08C062077C for ; Thu, 23 Jan 2020 19:51:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="KCK+MWqb" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 08C062077C 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]:60654 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iuiVq-0005zk-Vq for qemu-devel@archiver.kernel.org; Thu, 23 Jan 2020 14:51:35 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:41378) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iufe2-00052e-MC for qemu-devel@nongnu.org; Thu, 23 Jan 2020 11:47:51 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iufe1-0006bJ-6l for qemu-devel@nongnu.org; Thu, 23 Jan 2020 11:47:50 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:33639 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 1iufe1-0006b9-4Q for qemu-devel@nongnu.org; Thu, 23 Jan 2020 11:47:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579798068; 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=MuH5XRM9j7/njBUqjZRQrc2vGK70nTiSs8OqDoSc0g4=; b=KCK+MWqbC56EX82xDw0BSTQYVtEHwx900SRaSjkNbEiYZv6YI97I5qp1UGq/CiYvYYkkhL 4rSz1ZgG5xz4v2L04EAXqJNcb4v7QYu5kzcyRHUcvIiORg1L0maB7PCK46S1YQhOMwg2au mIhIdzvoDwQXrRPwES7uEiL5YTSoCPg= 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-125-G-b4wlZkPt6u3T0eYmpV0g-1; Thu, 23 Jan 2020 11:47:47 -0500 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 6DA3D8024EF for ; Thu, 23 Jan 2020 16:47:46 +0000 (UTC) Received: from dgilbert-t580.localhost (ovpn-116-110.ams2.redhat.com [10.36.116.110]) by smtp.corp.redhat.com (Postfix) with ESMTP id B9D5A2899A; Thu, 23 Jan 2020 16:47:45 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, stefanha@redhat.com Subject: [PULL 049/108] virtiofsd: sandbox mount namespace Date: Thu, 23 Jan 2020 16:45:31 +0000 Message-Id: <20200123164630.91498-50-dgilbert@redhat.com> In-Reply-To: <20200123164630.91498-1-dgilbert@redhat.com> References: <20200123164630.91498-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: G-b4wlZkPt6u3T0eYmpV0g-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 207.211.31.120 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 Reviewed-by: Daniel P. Berrang=C3=A9 Signed-off-by: Dr. David Alan Gilbert --- 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 e2e2211ea1..0570453eef 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -50,6 +50,7 @@ #include #include #include +#include #include #include #include @@ -1943,6 +1944,58 @@ 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); @@ -1952,6 +2005,39 @@ 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); @@ -2052,6 +2138,7 @@ 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); @@ -2075,6 +2162,8 @@ 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 2.24.1