netdev - Re: [PATCH] TCP: Add support for TCP Stealth

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Date:	Fri, 02 Jan 2015 00:31:53 +0100
From:	Julian Kirsch <kirschju@....in.tum.de>
To:	Stephen Hemminger <stephen@...workplumber.org>
CC:	netdev@...r.kernel.org,
	Christian Grothoff <christian@...thoff.org>,
	Jacob Appelbaum <jacob@...elbaum.net>
Subject: Re: [PATCH] TCP: Add support for TCP Stealth

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Hi Stephen,

thanks a lot for your input. I've reflected your suggestions in the
code: The mode member of the stealth struct is now a u8, integrity_len
is now unsigned (size_t), I've switched the integrity_len and
integrity_hash members in order to close the gaps in the struct (sorry
for wasting bits) and I removed the cast from the second parameter of
the memcopy you mentioned. While I totally agree with you that the
part of the iv-setup where we xor the hash, tsval and dport in is not
very readable, I'd argue that declaring and using a struct would make
the patch longer while the semantics of such a struct really are
needed only in context of a single function and therefore cannot be
reused. Do you think that accessing the elements with a macro (see
below) could be an alternative?

#define tcp_stealth_iv_integrity_hash(iv)	(((__be16 *)&iv)[2])

Best,
Julian

On 2015-01-01 20:10, Stephen Hemminger wrote:
> On Wed, 31 Dec 2014 22:54:59 +0100 Julian Kirsch
> <kirschju@....in.tum.de> wrote:
> 
>> +	memcpy(iv, (const __u8 *)daddr, +	       (daddr_size >
>> sizeof(iv)) ? sizeof(iv) : daddr_size); + +#ifdef
>> CONFIG_TCP_MD5SIG +	md5 = tp->af_specific->md5_lookup(sk, sk); 
>> +#else +	md5 = NULL; +#endif +	if (likely(sysctl_tcp_timestamps
>> && !md5) || tp->stealth.saw_tsval) +		tsval =
>> tp->stealth.mstamp.stamp_jiffies; + +	((__be16 *)iv)[2] ^=
>> cpu_to_be16(tp->stealth.integrity_hash);
> 
> Cast unnecessary on memcpy arg since it takes void *
> 
> Would be clearer to use a real structure or union not assignment to
> cast to setup iv. -- 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
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> 

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