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=-6.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=no 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 741C5C4363D for ; Tue, 6 Oct 2020 13:44:27 +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 CB83820760 for ; Tue, 6 Oct 2020 13:44:26 +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="JUIWSwey" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB83820760 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]:49322 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kPnGT-0002es-Hz for qemu-devel@archiver.kernel.org; Tue, 06 Oct 2020 09:44:25 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44726) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kPnFv-0002FR-I0 for qemu-devel@nongnu.org; Tue, 06 Oct 2020 09:43:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:45071) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kPnFt-00088l-M8 for qemu-devel@nongnu.org; Tue, 06 Oct 2020 09:43:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601991829; 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=wKfgzx42lITCiNHnkfrQCM90waahNcXGMIwe+DC4wwc=; b=JUIWSweyDIKNMtUj8Xj0VWjOKBtIIoQQ6IuKN4K6x8AKtOQnfToioE82RqPKXLGB9lYbTo 5xsi4mifBHI6QGSNP6dcNJhc69rHuqyllIJB/V2r4ISoh+xYfNVZRo6RiptsPbepb9mbMn AXGlTttghOziwBrduu1Sw6O8vfULZPQ= 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-543-PW_igdK5MKe-_UhwIN3Vdg-1; Tue, 06 Oct 2020 09:43:47 -0400 X-MC-Unique: PW_igdK5MKe-_UhwIN3Vdg-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 511619CC37 for ; Tue, 6 Oct 2020 13:43:46 +0000 (UTC) Received: from localhost (ovpn-113-0.ams2.redhat.com [10.36.113.0]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E28221002C02; Tue, 6 Oct 2020 13:43:39 +0000 (UTC) Date: Tue, 6 Oct 2020 15:43:38 +0200 From: Jens Freimann To: Stefan Hajnoczi Subject: Re: [PATCH] virtiofsd: avoid /proc/self/fd tempdir Message-ID: <20201006134338.GA49600@linux.fritz.box> References: <20201006095826.59813-1-stefanha@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201006095826.59813-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jfreimann@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=jfreimann@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 , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Oct 06, 2020 at 10:58:26AM +0100, Stefan Hajnoczi 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 Thanks Stefan, it fixes the problem we had! Tested-by: Jens Freimann Reviewed-by: Jens Freimann regards, Jens