linux-kernel - Re: [PATCH 04/10] usb: musb: ux500: harden checks for platform data

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Date:	Wed, 24 Apr 2013 18:00:28 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Lee Jones <lee.jones@...aro.org>
CC:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arnd@...db.de, linus.walleij@...ricsson.com,
	mian.yousaf.kaukab@...ricsson.com, Felipe Balbi <balbi@...com>,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH 04/10] usb: musb: ux500: harden checks for platform data

Hello.

On 24-04-2013 10:53, Lee Jones wrote:

>>>   	struct musb_hdrc_platform_data *plat = dev->platform_data;
>>> -	struct ux500_musb_board_data *data = plat->board_data;
>>> +	struct ux500_musb_board_data *data;

>>> -	param_array = data->dma_rx_param_array;
>>> +	param_array = (data) ? data->dma_rx_param_array : NULL;

>>     Why enclose a simple variable in parens?

> Because 'data' is a pointer, so it contains a memory location,

    Pointer points to memory location, not contains it.

> but if
> 'plat->board_data' is NULL, then 'data' will be NULL (essentially
> memory location 0x00000000).

    So what?

> So if we were to read-in to 'struct ux500_musb_board_data *data', by
> index 'dma_rx_param_array', which I believe is '0' in this case:

> struct ux500_musb_board_data {
>          void    **dma_rx_param_array;
>          void    **dma_tx_param_array;
>          bool (*dma_filter)(struct dma_chan *chan, void *filter_param);
> };

> ... then we're saying take the data from this memory location:

> param_array = *((0x00000000)->(0x0));

> Which will cause a kernel Oops, due to the fact that address 0x0 isn't
> allocated to us, so you get something like:

> "Unable to handle kernel NULL pointer dereference at virtual address 00000000"

    We're not dereferencing 'data', so I completely fail to follow you.

> Hope that helps.

    Not at all.

> Kind regards,
> Lee

WBR, Sergei

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