linux-kernel - Re: [PATCH RFC v2] slab: introduce kmalloc

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Message-Id: <8F83835C-366C-46AC-A50A-3F680B7D2D83@gmail.com>
Date:	Tue, 14 Feb 2012 11:30:52 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesper Juhl <jj@...osbits.net>, Jens Axboe <axboe@...nel.dk>,
	Pekka Enberg <penberg@...nel.org>,
	linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH RFC v2] slab: introduce kmalloc_array

On Feb 14, 2012, at 10:02 AM, Christoph Lameter wrote:
> We could also catch these issues with BUG() or WARN_ON() and then return
> zero.

You cannot have SAFE_ARRAY_SIZE return 0 when an integer overflow
occurs.

1) kmalloc(0) has a different semantics.

2) Using kmalloc(0) allows DoS attacks because often after kmalloc()
   there is some initialization code that writes to the allocated
   memory, such as:

   p = kmalloc(SAFE_ARRAY_SIZE(n, size), ...);
   for (i = 0; i < n; ++i)
       p[i] = ...;

Besides, BUG() still allows DoS attacks and WARN_ON() would flood
the log, especially if n is controlled from user space.  Neither
seems appropriate here.

- xi
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