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

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Message-ID: <CAJ5Y-ebG4YR2e3mYNCxGYiEvm3=9HTXp-5BXfQnuY7wvoipm-A@mail.gmail.com>
Date:	Thu, 10 Dec 2015 13:19:01 -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()

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>

Thanks,
Ashwin.
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