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

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Date:   Thu, 11 Feb 2021 12:58:48 +0100
From:   Maximilian Luz <luzmaximilian@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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 2/11/21 11:22 AM, Andy Shevchenko wrote:
> 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.

I can fix that if it bugs you.

> Also it's possible to annotate temporary variable and use it, but it seems not
> worth to do.

Now that you mention it, we already have the correct frame length in
payload.len. Let me draft up a new patch with that.

> 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.

That's the point though, no? The signature is

         u16 get_unaligned_le16(const void *p)

so we do want a pointer to the len member. So I believe that is correct.

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