From patchwork Tue Oct 6 09:58:26 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 271980 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=-7.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, MIME_BASE64_TEXT,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 26048C41604 for ; Tue, 6 Oct 2020 10:01:09 +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 4F80E20674 for ; Tue, 6 Oct 2020 10:01:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="bINGIaTX" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F80E20674 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]:53416 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kPjmN-0005pN-1R for qemu-devel@archiver.kernel.org; Tue, 06 Oct 2020 06:01:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45248) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kPjkU-0004LX-2g for qemu-devel@nongnu.org; Tue, 06 Oct 2020 05:59:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:48987) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kPjkR-0004Ik-FS for qemu-devel@nongnu.org; Tue, 06 Oct 2020 05:59:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601978346; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=ef4nEw92T7XryGjdWU85hpW8vouiPoI2HxKv7tDMlcM=; b=bINGIaTXGzr3dpWFul89zLPClE89pl2bH5Nbat/ZtQ8tlSr5VzU+H9AFLYORmrHtJmDsWi l8cV3tswa3yZrbtg0XgVNnXqSBLtIYqjC22udrggscHzCDyaru/oDh41uTmgO5UtToG54I 6n+m49lMQ19sdxle8uTTDSjMYaBMZgk= 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-326-uUA4l7IRPwGxYYRMrc-cxQ-1; Tue, 06 Oct 2020 05:59:04 -0400 X-MC-Unique: uUA4l7IRPwGxYYRMrc-cxQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ED72864080 for ; Tue, 6 Oct 2020 09:59:03 +0000 (UTC) Received: from localhost (ovpn-112-180.ams2.redhat.com [10.36.112.180]) by smtp.corp.redhat.com (Postfix) with ESMTP id DA0473A40; Tue, 6 Oct 2020 09:58:51 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH] virtiofsd: avoid /proc/self/fd tempdir Date: Tue, 6 Oct 2020 10:58:26 +0100 Message-Id: <20201006095826.59813-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=63.128.21.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/06 01:55:55 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.733, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MIME_BASE64_TEXT=1.741, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: , Cc: virtio-fs@redhat.com, Miklos Szeredi , Jens Freimann , "Dr. David Alan Gilbert" , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" In order to prevent /proc/self/fd escapes a temporary directory is created where /proc/self/fd is bind-mounted. This doesn't work on read-only file systems. Avoid the temporary directory by bind-mounting /proc/self/fd over /proc. This does not affect other processes since we remounted / with MS_REC | MS_SLAVE. /proc must exist and virtiofsd does not use it so it's safe to do this. Path traversal can be tested with the following function: static void test_proc_fd_escape(struct lo_data *lo) { int fd; int level = 0; ino_t last_ino = 0; fd = lo->proc_self_fd; for (;;) { struct stat st; if (fstat(fd, &st) != 0) { perror("fstat"); return; } if (last_ino && st.st_ino == last_ino) { fprintf(stderr, "inode number unchanged, stopping\n"); return; } last_ino = st.st_ino; fprintf(stderr, "Level %d dev %lu ino %lu\n", level, (unsigned long)st.st_dev, (unsigned long)last_ino); fd = openat(fd, "..", O_PATH | O_DIRECTORY | O_NOFOLLOW); level++; } } Before and after this patch only Level 0 is displayed. Without /proc/self/fd bind-mount protection it is possible to traverse parent directories. Fixes: 397ae982f4df4 ("virtiofsd: jail lo->proc_self_fd") Cc: Miklos Szeredi Cc: Jens Freimann Signed-off-by: Stefan Hajnoczi Reviewed-by: Dr. David Alan Gilbert Tested-by: Jens Freimann Reviewed-by: Jens Freimann --- tools/virtiofsd/passthrough_ll.c | 34 +++++++++++--------------------- 1 file changed, 11 insertions(+), 23 deletions(-) diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 0b229ebd57..6ae7ffcdd7 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -2393,8 +2393,6 @@ static void setup_wait_parent_capabilities(void) static void setup_namespaces(struct lo_data *lo, struct fuse_session *se) { pid_t child; - char template[] = "virtiofsd-XXXXXX"; - char *tmpdir; /* * Create a new pid namespace for *child* processes. We'll have to @@ -2458,33 +2456,23 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se) exit(1); } - tmpdir = mkdtemp(template); - if (!tmpdir) { - fuse_log(FUSE_LOG_ERR, "tmpdir(%s): %m\n", template); + /* + * We only need /proc/self/fd. Prevent ".." from accessing parent + * directories of /proc/self/fd by bind-mounting it over /proc. Since / was + * previously remounted with MS_REC | MS_SLAVE this mount change only + * affects our process. + */ + if (mount("/proc/self/fd", "/proc", NULL, MS_BIND, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, MS_BIND): %m\n"); exit(1); } - if (mount("/proc/self/fd", tmpdir, NULL, MS_BIND, NULL) < 0) { - fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, %s, MS_BIND): %m\n", - tmpdir); - exit(1); - } - - /* Now we can get our /proc/self/fd directory file descriptor */ - lo->proc_self_fd = open(tmpdir, O_PATH); + /* Get the /proc (actually /proc/self/fd, see above) file descriptor */ + lo->proc_self_fd = open("/proc", O_PATH); if (lo->proc_self_fd == -1) { - fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", tmpdir); + fuse_log(FUSE_LOG_ERR, "open(/proc, O_PATH): %m\n"); exit(1); } - - if (umount2(tmpdir, MNT_DETACH) < 0) { - fuse_log(FUSE_LOG_ERR, "umount2(%s, MNT_DETACH): %m\n", tmpdir); - exit(1); - } - - if (rmdir(tmpdir) < 0) { - fuse_log(FUSE_LOG_ERR, "rmdir(%s): %m\n", tmpdir); - } } /*