linux-kernel - Re: [PATCH] gpio: langwell: Prevent possible NULL pointer dereference in the demux handler.

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Date:	Mon, 7 May 2012 21:18:55 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Krzysztof Wilczynski <krzysztof.wilczynski@...ux.com>
cc:	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio: langwell: Prevent possible NULL pointer dereference
 in the demux handler.

On Sun, 6 May 2012, Krzysztof Wilczynski wrote:

> This is to address a possible NULL pointer dereference on a platform that might
> use this driver but its underlying IRQ chip does not provide an irq_eoi callback.
> 
> A commit 0766d20 added an conditional to the code, but then it was later
> super-seeded by commit 20e2aa9 which introduced number of helper functions
> for accessing various members of the irq_desc struct, but removed said
> conditional from the code.
> 
> This change will re-introduce conditional guarding against possible NULL
> pointer dereference caused by missing EIO handler.
> 
> Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@...ux.com>
> ---
>  drivers/gpio/gpio-langwell.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/gpio/gpio-langwell.c b/drivers/gpio/gpio-langwell.c
> index 00692e8..5749738 100644
> --- a/drivers/gpio/gpio-langwell.c
> +++ b/drivers/gpio/gpio-langwell.c
> @@ -260,7 +260,8 @@ static void lnw_irq_handler(unsigned irq, struct irq_desc *desc)
>  		}
>  	}
>  
> -	chip->irq_eoi(data);
> +	if (data)
> +		chip->irq_eoi(data);

And how does data, which is always set as long as the interrupt exist
prove that the chip has an eoi function?

Thanks,

	tglx
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