linux-kernel - Re: [PATCH] mailbox: pcc: fix channel calculation in get_pcc

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Date:	Fri, 15 Jan 2016 13:20:09 -0500
From:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
To:	Alexey Klimov <alexey.klimov@....com>
Cc:	Jassi Brar <jassisinghbrar@...il.com>,
	Sudeep Holla <sudeep.holla@....com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mailbox: pcc: fix channel calculation in get_pcc_channel()

Jassi,

On 10 December 2015 at 13:19, Ashwin Chaugule
<ashwin.chaugule@...aro.org> wrote:
> On 10 December 2015 at 12:28, Alexey Klimov <alexey.klimov@....com> wrote:
>> This patch fixes the calculation of pcc_chan for non-zero id.
>> After the compiler ignores the (unsigned long) cast the
>> pcc_mbox_channels pointer is type-cast and then the type-cast
>> offset is added which results in address outside of the range
>> leading to the kernel crashing.
>>
>> We might add braces and make it:
>>
>> pcc_chan = (struct mbox_chan *)
>>                 ((unsigned long) pcc_mbox_channels +
>>                 (id * sizeof(*pcc_chan)));
>>
>> but let's go with array approach here and use id as index.
>>
>> Tested on Juno board.
>>
>> Acked-by: Sudeep Holla <sudeep.holla@....com>
>> Signed-off-by: Alexey Klimov <alexey.klimov@....com>
>> ---
>>  drivers/mailbox/pcc.c | 8 +-------
>>  1 file changed, 1 insertion(+), 7 deletions(-)
>>
>> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
>> index 45d85ae..8f779a1 100644
>> --- a/drivers/mailbox/pcc.c
>> +++ b/drivers/mailbox/pcc.c
>> @@ -81,16 +81,10 @@ static struct mbox_controller pcc_mbox_ctrl = {};
>>   */
>>  static struct mbox_chan *get_pcc_channel(int id)
>>  {
>> -       struct mbox_chan *pcc_chan;
>> -
>>         if (id < 0 || id > pcc_mbox_ctrl.num_chans)
>>                 return ERR_PTR(-ENOENT);
>>
>> -       pcc_chan = (struct mbox_chan *)
>> -               (unsigned long) pcc_mbox_channels +
>> -               (id * sizeof(*pcc_chan));
>> -
>> -       return pcc_chan;
>> +       return &pcc_mbox_channels[id];
>>  }
>>
>
>
> Strange that we didn't catch this even with a non-zero id. But the
> change makes sense so..
>
> Acked-by: Ashwin Chaugule <ashwin.chaugule@...aro.org>

Can you please include this patch in your pull request to Linus?

Thanks,
Ashwin.