netdev - Re: [PATCH net-next] Revert "net/ipv6: add sysctl option accept_ra_min_hop

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Date:	Thu, 10 Sep 2015 11:40:37 +0200
From:	Sabrina Dubroca <sd@...asysnail.net>
To:	YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
Cc:	David Miller <davem@...emloft.net>,
	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
	liuhangbin@...il.com
Subject: Re: [PATCH net-next] Revert "net/ipv6: add sysctl option
 accept_ra_min_hop_limit"

2015-09-10, 14:52:45 +0900, YOSHIFUJI Hideaki wrote:
> Sabrina Dubroca wrote:
> > 2015-09-02, 16:11:10 -0700, David Miller wrote:
> >> The only thing I would entertain is potentially an adjustment of the
> >> default, working in concert with the TAHI folks to make sure their
> >> tests still pass with any new default.
> > 
> > Would you agree with a default of 64, as Florian suggested?
> 
> 1 was chosen to restore our behavior before introduction of current
> hoplimit check.  I am not in favor of changing that value.

But our old behavior had a security issue, which is why the >= current
check was introduced.


> Plus, 64 is too restrictive and 32 would be enough for global
> internet, IMHO.

I guess I could live with that, if 32 is indeed enough for everybody.


> > Can we still modify the behavior of this sysctl? It's already been in
> > Linus's tree for a while, but if we can, I would rather restrict the
> > values we let the user write to accept_ra_min_hop_limit, as anything
> > outside [0..255] does not really make sense.
> 
> [1..256], maybe, but it is not harmful to set outside the range.
> 0 is always ignored. If it is set to 256 or more, the option is
> completely ignored.

Not harmful, but maybe slightly misleading, and requires the "< 256"
check when processing a RA.


> > Allowing an RA to update the hop limit if
> > 
> >    current hop limit < RA.hop_limit < accept_ra_min_hop_limit
> > 
> > might also be desirable, but I'm not so sure about this case.
> > 
> > 
> 
> It might be... byt I don't think it is a good idea since it becomes
> more complex.

A bit more complex, yes.  But I don't think this should hold us back
if it results in better behavior.


Thanks,

-- 
Sabrina
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