linux-ext4 - Re: [PATCH] ext34: ensure do_split leaves enough free space in both blocks

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Message-ID: <46EEB7A4.9040903@sandeen.net>
Date:	Mon, 17 Sep 2007 12:21:40 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	ext4 development <linux-ext4@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	hooanon05@...oo.co.jp, Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH] ext34: ensure do_split leaves enough free space in both
 blocks

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.)

:(

-Eric
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