Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-bk0-f51.google.com ([209.85.214.51]:33121 "EHLO mail-bk0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754760Ab3HFOaZ (ORCPT ); Tue, 6 Aug 2013 10:30:25 -0400 Received: by mail-bk0-f51.google.com with SMTP id ji2so186431bkc.10 for ; Tue, 06 Aug 2013 07:30:23 -0700 (PDT) From: Miklos Szeredi To: rwheeler@redhat.com, avati@redhat.com, viro@ZenIV.linux.org.uk Cc: bfoster@redhat.com, dhowells@redhat.com, eparis@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, Trond.Myklebust@netapp.com, swhiteho@redhat.com, mszeredi@suse.cz Subject: [PATCH 2/4] vfs: check unlinked ancestors before mount Date: Tue, 6 Aug 2013 16:30:01 +0200 Message-Id: <1375799403-28544-3-git-send-email-miklos@szeredi.hu> In-Reply-To: <1375799403-28544-1-git-send-email-miklos@szeredi.hu> References: <1375799403-28544-1-git-send-email-miklos@szeredi.hu> Sender: linux-nfs-owner@vger.kernel.org List-ID: From: Miklos Szeredi We check submounts before doing d_drop() on a non-empty directory dentry in NFS (have_submounts()). But we do not exclude a racing mount. Nor do we prevent mounts to be added to the disconnected subtree using relative paths after the d_drop(). This patch fixes these issues by checking for unlinked (unhashed, non-root) ancestors before proceeding with the mount. This is done after setting DCACHE_MOUNTED on the soon-to-be mountpoint and with the rename seqlock taken for write. This ensures that the only one of have_submounts() or has_unlinked_ancestor() can succeed. Signed-off-by: Miklos Szeredi --- fs/dcache.c | 28 ++++++++++++++++++++++++++++ fs/internal.h | 1 + fs/namespace.c | 9 +++++++++ 3 files changed, 38 insertions(+) diff --git a/fs/dcache.c b/fs/dcache.c index ba429d9..eae7cc1 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1103,6 +1103,34 @@ rename_retry: } EXPORT_SYMBOL(have_submounts); +static bool __has_unlinked_ancestor(struct dentry *dentry) +{ + struct dentry *this; + + for (this = dentry; !IS_ROOT(this); this = this->d_parent) { + if (d_unhashed(this)) + return true; + } + return false; +} + +/* + * Called by mount code to check if the mountpoint is reachable (e.g. NFS can + * unhash a directory dentry and then the complete subtree can become + * unreachable). + */ +bool has_unlinked_ancestor(struct dentry *dentry) +{ + bool found; + + /* Need exclusion wrt. check_submounts_and_drop() */ + write_seqlock(&rename_lock); + found = __has_unlinked_ancestor(dentry); + write_sequnlock(&rename_lock); + + return found; +} + /* * Search the dentry child list of the specified parent, * and move any unused dentries to the end of the unused diff --git a/fs/internal.h b/fs/internal.h index 7c5f01c..d232355 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -126,6 +126,7 @@ extern int invalidate_inodes(struct super_block *, bool); * dcache.c */ extern struct dentry *__d_alloc(struct super_block *, const struct qstr *); +extern bool has_unlinked_ancestor(struct dentry *dentry); /* * read_write.c diff --git a/fs/namespace.c b/fs/namespace.c index 7b1ca9b..bb92a9c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -634,6 +634,15 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry) } dentry->d_flags |= DCACHE_MOUNTED; spin_unlock(&dentry->d_lock); + + if (has_unlinked_ancestor(dentry)) { + spin_lock(&dentry->d_lock); + dentry->d_flags &= ~DCACHE_MOUNTED; + spin_unlock(&dentry->d_lock); + kfree(mp); + return ERR_PTR(-ENOENT); + } + mp->m_dentry = dentry; mp->m_count = 1; list_add(&mp->m_hash, chain); -- 1.8.1.4