netdev - Re: [PATCH v2 net] net, ip_tunnel: fix interface lookup with no key

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Message-ID: <13f3cb64-4e5a-7792-91b6-795c89903fe3@6wind.com>
Date:   Fri, 27 Mar 2020 19:15:35 +0100
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     William Dauchy <w.dauchy@...teo.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net] net, ip_tunnel: fix interface lookup with no key

Le 27/03/2020 à 15:54, William Dauchy a écrit :
> when creating a new ipip interface with no local/remote configuration,
> the lookup is done with TUNNEL_NO_KEY flag, making it impossible to
> match the new interface (only possible match being fallback or metada
> case interface); e.g: `ip link add tunl1 type ipip dev eth0`
> 
> To fix this case, adding a flag check before the key comparison so we
> permit to match an interface with no local/remote config; it also avoids
> breaking possible userland tools relying on TUNNEL_NO_KEY flag and
> uninitialised key.
> 
> context being on my side, I'm creating an extra ipip interface attached
> to the physical one, and moving it to a dedicated namespace.
> 
> Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
> Signed-off-by: William Dauchy <w.dauchy@...teo.com>
> ---
>  net/ipv4/ip_tunnel.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index 74e1d964a615..b30485615426 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -142,11 +142,8 @@ struct ip_tunnel *ip_tunnel_lookup(struct ip_tunnel_net *itn,
>  			cand = t;
>  	}
>  
> -	if (flags & TUNNEL_NO_KEY)
> -		goto skip_key_lookup;
> -
>  	hlist_for_each_entry_rcu(t, head, hash_node) {
> -		if (t->parms.i_key != key ||
> +		if ((flags & TUNNEL_KEY && t->parms.i_key != key) ||
I saw this flag, and frankly, having a flag named TUNNEL_KEY and another named
TUNNEL_NO_KEY is an horrible API design.

But I prefer to be conservative and avoid (ugly) surprise, thus I think it's
better to keep TUNNEL_NO_KEY.


Regards,
Nicolas