netdev - Re: [PATCH net] fib_rules: don't break ECN with TOS rules

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Message-Id: <1465691900.3002733.634955425.22770D5E@webmail.messagingengine.com>
Date:	Sun, 12 Jun 2016 02:38:20 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Julian Anastasov <ja@....bg>
Cc:	netdev@...r.kernel.org, Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net] fib_rules: don't break ECN with TOS rules

On Sun, Jun 12, 2016, at 02:36, Hannes Frederic Sowa wrote:
> On Sun, Jun 12, 2016, at 02:09, Julian Anastasov wrote:
> > 
> > 	Hello,
> > 
> > On Sat, 11 Jun 2016, Hannes Frederic Sowa wrote:
> > 
> > > Users of ToS rules could accidentally break ECN, this patch tries to
> > > fix this in a way so we don't break shell scripts depending on the old
> > > behavior while still being transparent to ECN. This quietly fixes ECN
> > > behavior for old setups.
> > > 
> > > For IPv6 we have no check if we check for ECN bits, in IPv4 we only
> > > check for the last bit, which is specified to be '0' from pre-DSCP times
> > > (because of implementation confusion).
> > > 
> > > This patch changes fib rules in a way that matches only for ecn bits
> > > will never match from now on (I consider them illegal), as we simply
> > > ignore those rules (it was easier to explain in a pr_warn). Opinions?
> > 
> > 	Well, may be the confusion comes from commit 89aef8921bfb
> > ("ipv4: Delete routing cache.") where the 'tos &= IPTOS_RT_MASK;'
> > line is lost from ip_route_input_common. I think, we should
> > add it back, so that we can properly match input routes with rules
> > that specify tos value. Old kernels didn't stored ECN bits in
> > flowi4_tos in the input path, so we should do the same.
> 
> I would love to have done that but was fearing problems with user space
> compatibility. Also IPTOS_RT_MASK is not enough for filtering, we need
> to check for the whole INET_ECN_MASK.

Correction: IPTOS_RT_MASK would be fine, but fib4_rule_configure uses
IPTOS_TOS_MASK.

Bye,
Hannes