linux-kernel - Re: [PATCH] ext34: ensure do_split leaves enough free space in both blocks

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Date:	Mon, 17 Sep 2007 13:30:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Sandeen <sandeen@...deen.net>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	ext4 development <linux-ext4@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	hooanon05@...oo.co.jp, "Theodore Ts'o" <tytso@....edu>
Subject: Re: [PATCH] ext34: ensure do_split leaves enough free space in both
 blocks

On Mon, 17 Sep 2007 12:21:40 -0500
Eric Sandeen <sandeen@...deen.net> wrote:

> Eric Sandeen wrote:
> > The do_split() function for htree dir blocks is intended to split a
> > leaf block to make room for a new entry.  It sorts the entries in the
> > original block by hash value, then moves the last half of the entries to 
> > the new block - without accounting for how much space this actually moves.  
> > (IOW, it moves half of the entry *count* not half of the entry *space*).
> > If by chance we have both large & small entries, and we move only the 
> > smallest entries, and we have a large new entry to insert, we may not have 
> > created enough space for it.
> 
> (btw, the upshot of this is that in add_dirent_to_buf(),
> memcpy(de->name, name, namelen) will overshoot the buffer and actually
> corrupt memory.)

Nice!

So this looks like 2.6.22 and 2.6.23 material, but the timing is getting
pretty squeezy.  Could people please give this change an extra-close
review, let me know?

Thanks.
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