Subject: Re: [PATCH RFC v2] slab: introduce kmalloc_array
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From: Xi Wang <xi.wang@gmail.com>
In-Reply-To: <alpine.DEB.2.00.1202140858080.20013@router.home>
Date: Tue, 14 Feb 2012 11:30:52 -0500
Cc: Dan Carpenter <dan.carpenter@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jesper Juhl <jj@chaosbits.net>, Jens Axboe <axboe@kernel.dk>,
        Pekka Enberg <penberg@kernel.org>, linux-kernel@vger.kernel.org,
        Matt Mackall <mpm@selenic.com>, David Rientjes <rientjes@google.com>
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To: Christoph Lameter <cl@linux.com>
Sender: linux-kernel-owner@vger.kernel.org
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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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