linux-ext4 - confusion in validation of rec_len in ext2_add

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Message-ID: <ea11fea30812292145n2f484706refbe7bebaeb44e77@mail.gmail.com>
Date:	Tue, 30 Dec 2008 11:15:51 +0530
From:	"Manish Katiyar" <mkatiyar@...il.com>
To:	Kernelnewbies <kernelnewbies@...linux.org>,
	Linux-Ext4 <linux-ext4@...r.kernel.org>
Subject: confusion in validation of rec_len in ext2_add_link

Hi,

I was trying to understand the purpose of the below check for
validating rec_len in the function ext2_add_link(). Before reaching
line 515 we call ext2_get_page() which checks for valid entries on the
page and thus validates the rec_len too. And then we call the
lock_page(), so is this check redundant or to avoid cases when
something could have changed on the page between the lines 497 and 501
?

ext2_add_link() {

........	
497            page = ext2_get_page(dir, n, 0);
499	        	if (IS_ERR(page))
500			goto out;
501		    lock_page(page);
.........
515			if (de->rec_len == 0) {
516				ext2_error(dir->i_sb, __func__,
517					"zero-length directory entry");
518				err = -EIO;
519				goto out_unlock;
520			}

..........
}

Thanks -
Manish
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