netdev - Re: [PATCH net 1/2] ipv6: make exception cache less predictible

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Date:   Sun, 29 Aug 2021 17:39:17 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>, Willy Tarreau <w@....eu>,
        Keyu Man <kman001@....edu>, David Ahern <dsahern@...nel.org>,
        Wei Wang <weiwan@...gle.com>, Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH net 1/2] ipv6: make exception cache less predictible

On 8/29/21 3:16 PM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Even after commit 4785305c05b2 ("ipv6: use siphash in rt6_exception_hash()"),
> an attacker can still use brute force to learn some secrets from a victim
> linux host.
> 
> One way to defeat these attacks is to make the max depth of the hash
> table bucket a random value.
> 
> Before this patch, each bucket of the hash table used to store exceptions
> could contain 6 items under attack.
> 
> After the patch, each bucket would contains a random number of items,
> between 6 and 10. The attacker can no longer infer secrets.
> 
> This is slightly increasing memory size used by the hash table,
> we do not expect this to be a problem.
> 
> Following patch is dealing with the same issue in IPv4.
> 
> Fixes: 35732d01fe31 ("ipv6: introduce a hash table to store dst cache")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Keyu Man <kman001@....edu>
> Cc: Wei Wang <weiwan@...gle.com>
> Cc: Martin KaFai Lau <kafai@...com>
> ---
>  net/ipv6/route.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 

Reviewed-by: David Ahern <dsahern@...nel.org>