linux-kernel - Re: 2.6.22-rc2-mm1 NTFS & SLUB related fix

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Message-Id: <20070525000115.e24e027a.akpm@linux-foundation.org>
Date:	Fri, 25 May 2007 00:01:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"young dave" <hidave.darkstar@...il.com>
Cc:	"Christoph Lameter" <clameter@....com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Anton Altaparmakov" <aia21@...tab.net>
Subject: Re: 2.6.22-rc2-mm1 NTFS & SLUB related fix

On Fri, 25 May 2007 06:48:34 +0000 "young dave" <hidave.darkstar@...il.com> wrote:

> Yes, I'm sure.  but the patch in top post of mine works, the diffrence
> is using kzalloc and remove the  "ni->name[i] = 0;" line.
> 

Let's walk through the existing code:

		i = na->name_len * sizeof(ntfschar);

now, i = na->name_len * 2

		ni->name = kmalloc(i + sizeof(ntfschar), GFP_ATOMIC);

we allocated (na->name_len * 2 + 2) bytes

		if (!ni->name)
			return -ENOMEM;
		memcpy(ni->name, na->name, i);

we copied (na->name_len * 2) bytes

		ni->name[i] = 0;

here, we zero the two bytes at byte offsets ((na->name_len * 2) * 2) and
((na->name_len * 2) * 2 + 1), and that is the bug.  We _want_ to zero
the two bytes at byte offsets (na->name_len * 2) and (na->name_len * 2 + 1),
which we can do in C via

		ni->name[na->name_len] = 0;

because sizeof(*(ni->name)) == 2.


So I'm still suspecting that you mistested that change.
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