linux-kernel - Re: PROBLEM: Corrupting d_count of target dentry, when rename directory to the directory which is mount point, or when rename directory which is mount point to the existing directory.

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Message-ID: <20110603231158.GR11521@ZenIV.linux.org.uk>
Date:	Sat, 4 Jun 2011 00:11:58 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dmitry Dmitriev <dimondmm@...dex.ru>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: Corrupting d_count of target dentry, when rename
 directory to the directory which is mount point, or when rename directory
 which is mount point to the existing directory.

> When new_dentry exist, i.e. 'target' is not NULL, and a mount point( or old dentry is a mount point ), then function set 'error' variable to -EBUSY( line 2581 ). After that function will call dput function for new_dentry( line 2595 ) without corresponding dget. In this case d_count of dentry become corrupted. In case when old dentry and new dentry are not mount points, dget for new dentry is called in dentry_unhash function.

What do you mean, without corresponding dget()?  It's done in dentry_unhash().

Oh, hell...  We don't call it in that case.  Right.  vfs_rmdir() used to
do dentry_unhash() before the checks for mountpoints, vfs_rename_other() -
only after.

The funny part is, it got accidentally fixed in this merge window.  -stable
still needs fixing - by moving dentry_unhash() down past the checks for
d_mountpoint().  Mainline should be OK now...
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