linux-kernel - Re: [PATCH] mm: dmapool: fix possible use after free in dmam_pool

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Date:	Mon, 6 Jun 2011 09:37:46 +0100
From:	Maxin B John <maxin.john@...il.com>
To:	eike-kernel@...tec.de
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, dima@...roid.com, willy@...ux.intel.com,
	segooon@...il.com, tj@...nel.org, jkosina@...e.cz,
	tglx@...utronix.de
Subject: Re: [PATCH] mm: dmapool: fix possible use after free in dmam_pool_destroy()

Hi,

On Thu, Jun 2, 2011 at 3:22 PM, Maxin B John <maxin.john@...il.com> wrote:
> On Thu, Jun 2, 2011 at 12:47 PM, Rolf Eike Beer <eike-kernel@...tec.de> wrote:
>> Maxin B John wrote:
>>> "dma_pool_destroy(pool)" calls "kfree(pool)". The freed pointer
>>> "pool" is again passed as an argument to the function "devres_destroy()".
>>> This patch fixes the possible use after free.
>>
>> The pool itself is not used there, only the address where the pool
>> has been.This will only lead to any trouble if something else is allocated to
>> the same place and inserted into the devres list of the same device between
>> the dma_pool_destroy() and devres_destroy().
>
> Thank you very much for explaining it in detail.
>
>> But I agree that this is bad style. But if you are going to change
>> this please also have a look at devm_iounmap() in lib/devres.c. Maybe also the
>> devm_*irq* functions need the same changes.
>
> As per your suggestion, I have made similar modifications for lib/devres.c and
> kernel/irq/devres.c
>
> CCed the maintainers of the respective files.
>
> Signed-off-by: Maxin B. John <maxin.john@...il.com>
> ---
> diff --git a/kernel/irq/devres.c b/kernel/irq/devres.c
> index 1ef4ffc..bd8e788 100644
> --- a/kernel/irq/devres.c
> +++ b/kernel/irq/devres.c
> @@ -87,8 +87,8 @@ void devm_free_irq(struct device *dev, unsigned int irq, void *dev_id)
>  {
>        struct irq_devres match_data = { irq, dev_id };
>
> -       free_irq(irq, dev_id);
>        WARN_ON(devres_destroy(dev, devm_irq_release, devm_irq_match,
>                               &match_data));
> +       free_irq(irq, dev_id);
>  }
>  EXPORT_SYMBOL(devm_free_irq);
> diff --git a/lib/devres.c b/lib/devres.c
> index 6efddf5..7c0e953 100644
> --- a/lib/devres.c
> +++ b/lib/devres.c
> @@ -79,9 +79,9 @@ EXPORT_SYMBOL(devm_ioremap_nocache);
>  */
>  void devm_iounmap(struct device *dev, void __iomem *addr)
>  {
> -       iounmap(addr);
>        WARN_ON(devres_destroy(dev, devm_ioremap_release, devm_ioremap_match,
>                               (void *)addr));
> +       iounmap(addr);
>  }
>  EXPORT_SYMBOL(devm_iounmap);
>

Could you please let me know your thoughts on this patch ?

Best Regards,
Maxin
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