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

From: Alexander Duyck <redacted>
Date: Fri, 10 Oct 2014 11:53:35 -0700

On 10/10/2014 11:22 AM, David Miller wrote:

quoted

From: David Miller <davem@davemloft.net>
Date: Fri, 10 Oct 2014 14:15:59 -0400 (EDT)

quoted

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.

No reason, just a thinko, my brain implemented this as if skb_header_pointer
worked like skb_pull :-/