linux-kernel - Re: [PATCH] platform/surface: aggregator: Fix access of unaligned value

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Date:   Thu, 11 Feb 2021 12:22:56 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Maximilian Luz <luzmaximilian@...il.com>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-test-robot <lkp@...el.com>
Subject: Re: [PATCH] platform/surface: aggregator: Fix access of unaligned
 value

On Thu, Feb 11, 2021 at 12:04:11AM +0100, Maximilian Luz wrote:
> The raw message frame length is unaligned and explicitly marked as
> little endian. It should not be accessed without the appropriatte
> accessor functions. Fix this.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Though a few nit-picks below.

> Reported-by: kernel-test-robot <lkp@...el.com>
> Fixes: c167b9c7e3d6 ("platform/surface: Add Surface Aggregator subsystem")
> Signed-off-by: Maximilian Luz <luzmaximilian@...il.com>
> ---
>  drivers/platform/surface/aggregator/ssh_packet_layer.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/surface/aggregator/ssh_packet_layer.c b/drivers/platform/surface/aggregator/ssh_packet_layer.c
> index 583315db8b02..9a78188d8d1c 100644
> --- a/drivers/platform/surface/aggregator/ssh_packet_layer.c
> +++ b/drivers/platform/surface/aggregator/ssh_packet_layer.c
> @@ -1774,7 +1774,8 @@ static size_t ssh_ptl_rx_eval(struct ssh_ptl *ptl, struct ssam_span *source)
>  		break;
>  	}
>  
> -	return aligned.ptr - source->ptr + SSH_MESSAGE_LENGTH(frame->len);
> +	return aligned.ptr - source->ptr
> +		+ SSH_MESSAGE_LENGTH(get_unaligned_le16(&frame->len));

I would leave + on previous line.
Also it's possible to annotate temporary variable and use it, but it seems not
worth to do.

Side question: Do you think the below is correct (& operator)?

        sp.len = get_unaligned_le16(&((struct ssh_frame *)sf.ptr)->len);

To me seems like you take an address to len member rather its value.

>  }
>  
>  static int ssh_ptl_rx_threadfn(void *data)

-- 
With Best Regards,
Andy Shevchenko