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=-11.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 79A94C4363D for ; Tue, 6 Oct 2020 11:05:12 +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 A77F62080A for ; Tue, 6 Oct 2020 11:05:11 +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="Xupc+1/I" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A77F62080A 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]:53002 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kPkmM-0007mf-Lv for qemu-devel@archiver.kernel.org; Tue, 06 Oct 2020 07:05:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60906) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kPklD-0007GH-0l for qemu-devel@nongnu.org; Tue, 06 Oct 2020 07:03:59 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:51268) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kPklA-0004LJ-DC for qemu-devel@nongnu.org; Tue, 06 Oct 2020 07:03:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601982235; 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: in-reply-to:in-reply-to:references:references; bh=8y9whln4LwEsuW+7p4mDqE3F7osGP+omK5Mro6quS+Q=; b=Xupc+1/IIqgqcvvRf+khO5wcTPi7bEAg9S5DraJfHaXuqOBGyEZLOnfgcthZPTNL7bj9sZ QPsn0e1UYaAFZeNskXKjEaV3n7DZH6lc4IZQeEkI2bYKvtyn7dMNmeMJWLhULUDyXmRh/F kiR5+yQtRyTtbghBUa1Hx+6W7MHNUz4= 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-415-4mi4e1jVOHy26_luL6mIJA-1; Tue, 06 Oct 2020 07:03:53 -0400 X-MC-Unique: 4mi4e1jVOHy26_luL6mIJA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7D25987950C for ; Tue, 6 Oct 2020 11:03:52 +0000 (UTC) Received: from work-vm (ovpn-114-216.ams2.redhat.com [10.36.114.216]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AFC8910013DB; Tue, 6 Oct 2020 11:03:41 +0000 (UTC) Date: Tue, 6 Oct 2020 12:03:39 +0100 From: "Dr. David Alan Gilbert" To: Stefan Hajnoczi Subject: Re: [PATCH] virtiofsd: avoid /proc/self/fd tempdir Message-ID: <20201006110339.GC3000@work-vm> References: <20201006095826.59813-1-stefanha@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201006095826.59813-1-stefanha@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/06 00:55:20 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=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 , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Stefan Hajnoczi (stefanha@redhat.com) wrote: > 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 Yes, getting rid of the tmpdir altogether seems better. Reviewed-by: Dr. David Alan Gilbert > --- > 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); > - } > } > > /* > -- > 2.26.2 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK