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

[Maximilian Luz]

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@xxxxxxxxxxxxxxx>
> Though a few nit-picks below.
>
> > Reported-by: kernel-test-robot <lkp@xxxxxxxxx>
> > Fixes: c167b9c7e3d6 ("platform/surface: Add Surface Aggregator subsystem")
> > Signed-off-by: Maximilian Luz <luzmaximilian@xxxxxxxxx>
> > ---
> >   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)