From: Eric Sandeen Subject: Re: [PATCH] ext34: ensure do_split leaves enough free space in both blocks Date: Mon, 17 Sep 2007 12:21:40 -0500 Message-ID: <46EEB7A4.9040903@sandeen.net> References: <46EEA5F4.3030806@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: ext4 development , Linux Kernel Mailing List , hooanon05@yahoo.co.jp, Andrew Morton To: Eric Sandeen Return-path: Received: from mx1.redhat.com ([66.187.233.31]:43889 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753015AbXIQRVp (ORCPT ); Mon, 17 Sep 2007 13:21:45 -0400 In-Reply-To: <46EEA5F4.3030806@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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