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

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.