netdev - Re: [PATCH] flow-dissector: Fix alignment issue in __skb_flow_get

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Date:	Fri, 10 Oct 2014 11:53:35 -0700
From:	Alexander Duyck <alexander.h.duyck@...hat.com>
To:	David Miller <davem@...emloft.net>, alexander.duyck@...il.com
CC:	eric.dumazet@...il.com, David.Laight@...LAB.COM,
	netdev@...r.kernel.org
Subject: Re: [PATCH] flow-dissector: Fix alignment issue in __skb_flow_get_ports

On 10/10/2014 11:22 AM, David Miller wrote:
> From: David Miller <davem@...emloft.net>
> Date: Fri, 10 Oct 2014 14:15:59 -0400 (EDT)
>
>> Your original code works because you do things like "byte[12] & 0xf0" to
>> extract these fields.
> Changing that th->doff sequence to instead be:
>
> 		const u8 *bp;
> 		u8 buf[13];
>
> 		bp = __skb_header_pointer(skb, poff, sizeof(buf),
> 					  data, hlen, &buf);
> 		if (!bp)
> 			return poff;
>
> 		poff += max_t(u32, sizeof(struct tcphdr), (bp[12] & 0xf0) >> 2);
> 		break;
>
> on top of your v3 patch works for me.
>
> Please double-check my calculations.

Any reason why you are grabbing all 13 bytes instead of just the 1 we 
care about?  Seems like we could just use a u8 buf instead of the array 
since we are only grabbing doff.

Thanks,

Alex
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