From patchwork Wed Mar 15 01:40:44 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 9624697 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 4FEE160424 for ; Wed, 15 Mar 2017 01:40:56 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 40C3A285D1 for ; Wed, 15 Mar 2017 01:40:56 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 35552285F3; Wed, 15 Mar 2017 01:40:56 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_TVD_MIME_EPI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id AB821285D1 for ; Wed, 15 Mar 2017 01:40:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750898AbdCOBky (ORCPT ); Tue, 14 Mar 2017 21:40:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:36078 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750851AbdCOBky (ORCPT ); Tue, 14 Mar 2017 21:40:54 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 70A80AD70; Wed, 15 Mar 2017 01:40:52 +0000 (UTC) From: NeilBrown To: "J. Bruce Fields" Date: Wed, 15 Mar 2017 12:40:44 +1100 Cc: Linux NFS Subject: [PATCH] NFS: don't try to cross a mountpount when there isn't one there. Message-ID: <87fuife2qr.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP consider the sequence of commands: mkdir -p /import/nfs /import/bind /import/etc mount --bind / /import/bind mount --make-private /import/bind mount --bind /import/etc /import/bind/etc exportfs -o rw,no_root_squash,crossmnt,async,no_subtree_check localhost:/ mount -o vers=4 localhost:/ /import/nfs ls -l /import/nfs/etc You would not expect this to report a stale file handle. Yet it does. The manipulations under /import/bind cause the dentry for /etc to get the DCACHE_MOUNTED flag set, even though nothing is mounted on /etc. This causes nfsd to call nfsd_cross_mnt() even though there is no mountpoint. So an upcall to mountd for "/etc" is performed. The 'crossmnt' flag on the export of / causes mountd to report that /etc is exported as it is a descendant of /. It assumes the kernel wouldn't ask about something that wasn't a mountpoint. The filehandle returned identifies the filesystem and the inode number of /etc. When this filehandle is presented to rpc.mountd, via "nfsd.fh", the inode cannot be found associated with any name in /etc/exports, or with any mountpoint listed by getmntent(). So rpc.mountd says the filehandle doesn't exist. Hence ESTALE. This is fixed by teaching nfsd not to trust DCACHE_MOUNTD too much. It is just a hint, not a guarantee. Change nfsd_mountpoint() to return '1' for a certain mountpoint, '2' for a possible mountpoint, and 0 otherwise. Then change nfsd_crossmnt() to check if follow_down() actually found a mountpount and, if not, to avoid performing a lookup if the location is not known to certainly require an export-point. Signed-off-by: NeilBrown --- fs/nfsd/vfs.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index 19d50f600e8d..04cafaa94bf7 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -94,6 +94,12 @@ nfsd_cross_mnt(struct svc_rqst *rqstp, struct dentry **dpp, err = follow_down(&path); if (err < 0) goto out; + if (path.mnt == exp->ex_path.mnt && path.dentry == dentry && + nfsd_mountpoint(dentry, exp) == 2) { + /* This is only a mountpoint in some other namespace */ + path_put(&path); + goto out; + } exp2 = rqst_exp_get_by_name(rqstp, &path); if (IS_ERR(exp2)) { @@ -167,16 +173,26 @@ static int nfsd_lookup_parent(struct svc_rqst *rqstp, struct dentry *dparent, st /* * For nfsd purposes, we treat V4ROOT exports as though there was an * export at *every* directory. + * We return: + * '1' if this dentry *must* be an export point, + * '2' if it might be, if there is really a mount here, and + * '0' if there is no chance of an export point here. */ int nfsd_mountpoint(struct dentry *dentry, struct svc_export *exp) { - if (d_mountpoint(dentry)) + if (!d_inode(dentry)) + return 0; + if (exp->ex_flags & NFSEXP_V4ROOT) return 1; if (nfsd4_is_junction(dentry)) return 1; - if (!(exp->ex_flags & NFSEXP_V4ROOT)) - return 0; - return d_inode(dentry) != NULL; + if (d_mountpoint(dentry)) + /* + * Might only be a mountpoint in a different namespace, + * but we need to check. + */ + return 2; + return 0; } __be32