Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965138Ab3IEJpi (ORCPT ); Thu, 5 Sep 2013 05:45:38 -0400 Received: from mail-ea0-f178.google.com ([209.85.215.178]:53192 "EHLO mail-ea0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935591Ab3IEJoz (ORCPT ); Thu, 5 Sep 2013 05:44:55 -0400 From: Miklos Szeredi To: viro@ZenIV.linux.org.uk Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mszeredi@suse.cz, David Howells , Steven Whitehouse , Trond Myklebust , Greg Kroah-Hartman Subject: [PATCH 04/11] vfs: check unlinked ancestors before mount Date: Thu, 5 Sep 2013 11:44:37 +0200 Message-Id: <1378374284-1484-5-git-send-email-miklos@szeredi.hu> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1378374284-1484-1-git-send-email-miklos@szeredi.hu> References: <1378374284-1484-1-git-send-email-miklos@szeredi.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3328 Lines: 110 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 check_submounts_and_drop() or has_unlinked_ancestor() can succeed. Signed-off-by: Miklos Szeredi CC: David Howells CC: Steven Whitehouse CC: Trond Myklebust CC: Greg Kroah-Hartman --- fs/dcache.c | 35 +++++++++++++++++++++++++++++++++++ fs/internal.h | 1 + fs/namespace.c | 9 +++++++++ 3 files changed, 45 insertions(+) diff --git a/fs/dcache.c b/fs/dcache.c index d05f46c..eb0ada5 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1159,6 +1159,41 @@ int have_submounts(struct dentry *parent) } 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) { + int is_unhashed; + + /* Need exclusion wrt. check_submounts_and_drop() */ + spin_lock(&this->d_lock); + is_unhashed = d_unhashed(this); + spin_unlock(&this->d_lock); + + if (is_unhashed) + 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 a45ba4f..91b1c39 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/