netdev - Re: [PATCH v2 net-next 4/4] ipv4: Retire global IPv4 hash table inet_addr

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Message-ID: <20241008170906.98082-1-kuniyu@amazon.com>
Date: Tue, 8 Oct 2024 10:09:06 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <dsahern@...nel.org>, <kuba@...nel.org>,
	<kuni1840@...il.com>, <kuniyu@...zon.com>, <netdev@...r.kernel.org>,
	<pabeni@...hat.com>
Subject: Re: [PATCH v2 net-next 4/4] ipv4: Retire global IPv4 hash table inet_addr_lst.

From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 8 Oct 2024 13:21:08 +0200
> On Tue, Oct 8, 2024 at 1:10 PM Paolo Abeni <pabeni@...hat.com> wrote:
> >
> > On 10/4/24 21:59, Kuniyuki Iwashima wrote:
> > > No one uses inet_addr_lst anymore, so let's remove it.
> > >
> > > While at it, we can remove net_hash_mix() from the hash calculation.
> >
> > Is that really safe? it will make hash collision predictable in a
> > deterministic way.
> >
> > FTR, IPv6 still uses the net seed.
> 
> I was planning to switch ipv6 to a safer hash, because the
> ipv6_addr_hash() is also predictable.
> It is easy for an attacker to push 10000 ipv6 addresses on the same slot.
> 
> We have netns isolation for sure, but being able to use a big amount
> of cpu cycles in the kernel is an issue.

I'll keep inet_addr_hash() as is in patch 4, and once the IPv6
changes are applied, I'll post another patch to follow the change
in IPv4 using __ipv4_addr_hash().

static inline u32 __ipv4_addr_hash(const struct net *net, __be32 ip)
{
	return jhash_1word((__force u32)ip, net_hash_mix(net));
}

Thanks!