From patchwork Thu Dec 12 16:38:09 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "Dr. David Alan Gilbert" X-Patchwork-Id: 1208693 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="X5v6ztYK"; 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 47YglN5zBPz9sNH for ; Fri, 13 Dec 2019 04:29:19 +1100 (AEDT) Received: from localhost ([::1]:34666 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ifSH2-00043S-NB for incoming@patchwork.ozlabs.org; Thu, 12 Dec 2019 12:29:12 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:52505) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ifRVv-00068E-5D for qemu-devel@nongnu.org; Thu, 12 Dec 2019 11:40:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ifRVt-0002aO-Hi for qemu-devel@nongnu.org; Thu, 12 Dec 2019 11:40:31 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:29730 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ifRVt-0002Zc-Cp for qemu-devel@nongnu.org; Thu, 12 Dec 2019 11:40:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1576168829; 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=gcHRGaMQySuscGEZQmOdWv9vhYbjHTW0hTRIDvEx2xA=; b=X5v6ztYKejFU1jdtkhXYlwshNeDMSXVmGSbB6n1JaOOlCLuk5MhU8rizsfps52Ysx9xrq3 e5A0dq9sWAR1mlGoL0uTXv+CQ51HyLyb9h7sgzmwPLXvAe5FxFnCyu5HXbCeji0pVK5XZL iBdBSi10P1DxInIQEyAl5R1N1uBkmDM= 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-265-8Mk_Z5igPCWYyTCmEP8dzA-1; Thu, 12 Dec 2019 11:40:27 -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 BAE631800D45 for ; Thu, 12 Dec 2019 16:40:26 +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 E429160BF3; Thu, 12 Dec 2019 16:40:25 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, stefanha@redhat.com, vgoyal@redhat.com Subject: [PATCH 049/104] virtiofsd: move to a new pid namespace Date: Thu, 12 Dec 2019 16:38:09 +0000 Message-Id: <20191212163904.159893-50-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: 8Mk_Z5igPCWYyTCmEP8dzA-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: 207.211.31.81 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 virtiofsd needs access to /proc/self/fd. Let's move to a new pid namespace so that a compromised process cannot see another other processes running on the system. One wrinkle in this approach: unshare(CLONE_NEWPID) affects *child* processes and not the current process. Therefore we need to fork the pid 1 process that will actually run virtiofsd and leave a parent in waitpid(2). This is not the same thing as daemonization and parent processes should not notice a difference. Signed-off-by: Stefan Hajnoczi Reviewed-by: Daniel P. Berrangé --- tools/virtiofsd/passthrough_ll.c | 134 ++++++++++++++++++++----------- 1 file changed, 86 insertions(+), 48 deletions(-) diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 135a99f2fd..754ef2618b 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -50,7 +50,10 @@ #include #include #include +#include #include +#include +#include #include #include @@ -1927,24 +1930,95 @@ static void print_capabilities(void) } /* - * Called after our UNIX domain sockets have been created, now we can move to - * an empty network namespace to prevent TCP/IP and other network activity in - * case this process is compromised. + * Move to a new mount, net, and pid namespaces to isolate this process. */ -static void setup_net_namespace(void) +static void setup_namespaces(struct lo_data *lo, struct fuse_session *se) { - if (unshare(CLONE_NEWNET) != 0) { - fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWNET): %m\n"); + pid_t child; + + /* + * Create a new pid namespace for *child* processes. We'll have to + * fork in order to enter the new pid namespace. A new mount namespace + * is also needed so that we can remount /proc for the new pid + * namespace. + * + * Our UNIX domain sockets have been created. Now we can move to + * an empty network namespace to prevent TCP/IP and other network + * activity in case this process is compromised. + */ + if (unshare(CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET) != 0) { + fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWPID | CLONE_NEWNS): %m\n"); + exit(1); + } + + child = fork(); + if (child < 0) { + fuse_log(FUSE_LOG_ERR, "fork() failed: %m\n"); + exit(1); + } + if (child > 0) { + pid_t waited; + int wstatus; + + /* The parent waits for the child */ + do { + waited = waitpid(child, &wstatus, 0); + } while (waited < 0 && errno == EINTR && !se->exited); + + /* We were terminated by a signal, see fuse_signals.c */ + if (se->exited) { + exit(0); + } + + if (WIFEXITED(wstatus)) { + exit(WEXITSTATUS(wstatus)); + } + + exit(1); + } + + /* Send us SIGTERM when the parent thread terminates, see prctl(2) */ + prctl(PR_SET_PDEATHSIG, SIGTERM); + + /* + * If the mounts have shared propagation then we want to opt out so our + * mount changes don't affect the parent mount namespace. + */ + if (mount(NULL, "/", NULL, MS_REC | MS_SLAVE, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_SLAVE): %m\n"); + exit(1); + } + + /* The child must remount /proc to use the new pid namespace */ + if (mount("proc", "/proc", "proc", + MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RELATIME, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(/proc): %m\n"); + exit(1); + } + + /* Now we can get our /proc/self/fd directory file descriptor */ + lo->proc_self_fd = open("/proc/self/fd", O_PATH); + if (lo->proc_self_fd == -1) { + fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n"); exit(1); } } -/* This magic is based on lxc's lxc_pivot_root() */ -static void setup_pivot_root(const char *source) +/* + * Make the source directory our root so symlinks cannot escape and no other + * files are accessible. Assumes unshare(CLONE_NEWNS) was already called. + */ +static void setup_mounts(const char *source) { int oldroot; int newroot; + 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); + } + + /* This magic is based on lxc's lxc_pivot_root() */ oldroot = open("/", O_DIRECTORY | O_RDONLY | O_CLOEXEC); if (oldroot < 0) { fuse_log(FUSE_LOG_ERR, "open(/): %m\n"); @@ -1991,47 +2065,14 @@ static void setup_pivot_root(const char *source) close(oldroot); } -static void setup_proc_self_fd(struct lo_data *lo) -{ - lo->proc_self_fd = open("/proc/self/fd", O_PATH); - if (lo->proc_self_fd == -1) { - fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n"); - exit(1); - } -} - -/* - * 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) +static void setup_sandbox(struct lo_data *lo, struct fuse_session *se) { - setup_net_namespace(); - setup_mount_namespace(lo->source); + setup_namespaces(lo, se); + setup_mounts(lo->source); } int main(int argc, char *argv[]) @@ -2155,10 +2196,7 @@ int main(int argc, char *argv[]) fuse_daemonize(opts.foreground); - /* Must be after daemonize to get the right /proc/self/fd */ - setup_proc_self_fd(&lo); - - setup_sandbox(&lo); + setup_sandbox(&lo, se); /* Block until ctrl+c or fusermount -u */ ret = virtio_loop(se);