linux-kernel - Re: [PATCH] dma: fix up broken comparison in dma_alloc_from

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Message-Id: <20090127134831.3dd04182.akpm@linux-foundation.org>
Date:	Tue, 27 Jan 2009 13:48:31 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	adrian@...golddream.dyndns.info, lkmladrian@...il.com,
	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	penberg@...helsinki.fi, dbaryshkov@...il.com,
	penguin-kernel@...ove.sakura.ne.jp, lg@...x.de, hannes@...xchg.org
Subject: Re: [PATCH] dma: fix up broken comparison in
 dma_alloc_from_coherent

On Wed, 21 Jan 2009 17:11:19 +0900
Paul Mundt <lethal@...ux-sh.org> wrote:

> @@ -118,31 +118,32 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
>  	mem = dev->dma_mem;
>  	if (!mem)
>  		return 0;
> -	if (unlikely(size > mem->size))
> - 		return 0;
> +
> +	*ret = NULL;
> +
> +	if (unlikely(size > (mem->size << PAGE_SHIFT)))
> +		goto err;

Looks a bit broken on 64-bit.

`size' is ssize_t (long).

`mem->size' is `int'.

The left shift can overflow and cause badnesses.

> +	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
> +	*ret = mem->virt_base + (pageno << PAGE_SHIFT);

Ditto.


Maybe it's a can't-happen (why?), but...
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