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

[David Miller <davem@davemloft.net>]

From: Sabrina Dubroca <sd@queasysnail.net>
Date: Wed, 2 Sep 2015 11:43:01 +0200

> This reverts commit 8013d1d7eafb0589ca766db6b74026f76b7f5cb4.
> 
> There are several issues with this patch.
> It completely cancels the security changes introduced by 6fd99094de2b
> ("ipv6: Don't reduce hop limit for an interface").
> The current default value (min hop limit = 1) can result in the same
> denial of service that 6fd99094de2b prevents, but it is hard to define
> a correct and sane default value.
> More generally, it is yet another IPv6 sysctl, and we already have too
> many.
> 
> This was introduced to satisfy a TAHI test case which, in my opinion, is
> too strict, turning the RFC's "SHOULD" into a "MUST":
> 
>     If the received Cur Hop Limit value is non-zero, the host
>     SHOULD set its CurHopLimit variable to the received value.
> 
> The behavior of this sysctl is wrong in multiple ways.  Some are
> fixable, but let's not rush this commit into mainline, and revert this
> while we still can, then we can come up with a better solution.
> 
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>

I don't agree with this revert.

If you look at the original commit, the quoted RFC recommends adding
a configurable method to protect against this.

And that's exactly what the commit you are trying to revert is doing.

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.

Thanks.