linux-ext4 - [PATCH 1/4] vfs: Avoid creation of directory loops for corrupted filesystems

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Message-Id: <1338322067-17566-2-git-send-email-jack@suse.cz>
Date:	Tue, 29 May 2012 22:07:44 +0200
From:	Jan Kara <jack@...e.cz>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: [PATCH 1/4] vfs: Avoid creation of directory loops for corrupted filesystems

When a directory hierarchy is corrupted (e. g. due to a bit flip on the media),
it can happen that it contains loops of directories. That creates possibilities
for deadlock when locking directories.

Fix the problem by checking in d_splice_alias() that when we splice a
directory, it does not have any other connected alias.

Reported-by: Sami Liedes <sami.liedes@....fi>
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/dcache.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 4435d8b..ca31a1e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1658,6 +1658,10 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 			d_move(new, dentry);
 			iput(inode);
 		} else {
+			if (unlikely(!list_empty(&inode->i_dentry))) {
+				spin_unlock(&inode->i_lock);
+				return ERR_PTR(-EIO);
+			}
 			/* already taking inode->i_lock, so d_add() by hand */
 			__d_instantiate(dentry, inode);
 			spin_unlock(&inode->i_lock);
-- 
1.7.1

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