netdev - Re: [PATCH] tcp: make urg+gso work for real this time

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <E1LCtP8-0004QO-Bp@gondolin.me.apana.org.au>
Date:	Wed, 17 Dec 2008 21:13:22 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	ilpo.jarvinen@...sinki.fi (Ilpo J??rvinen)
Cc:	herbert@...dor.apana.org.au, davem@...emloft.net,
	netdev@...r.kernel.org, ptesarik@...e.cz
Subject: Re: [PATCH] tcp: make urg+gso work for real this time

Ilpo J??rvinen <ilpo.jarvinen@...sinki.fi> wrote:
> 
> This is certainly nice and possible but as mention earlier, the harder 
> problem is that the urg_ptr is only 16-bits so there will be still be 
> problem if the urgent seq-64k mark is within a super-skb as tail segments 
> need urg while the head ones won't. I think we would need out-of-band 
> means to communicate the extra bit (17th) from tcp if we want to solve 
> that one. It would be rather easy to change TCP to only do splitting for 
> that particular skb though and keep everything else intact.

I think you've got it the wrong way around.  The test for setting
urg_ptr is:

        if (unlikely(tcp_urg_mode(tp) &&
                     between(tp->snd_up, tcb->seq + 1, tcb->seq + 0xFFFF))) {

So if this is true for the super-packet, then by definition it is
also true for the first packet.  In fact, it will be true for the
first n packets where

	tcb->seq + n * mss + 1 <= tp->snd_up

The only time when this will fall apart is if we had super-packets
bigger than 64K.  Fortunately or unfortunately that is a long way
off.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html