Re: [PATCH] tcp: md5: Fix overlap between vrf and non-vrf keys

[Leonard Crestez]

On 07.10.2021 04:14, David Ahern wrote:
> On 10/6/21 11:48 AM, Leonard Crestez wrote:
> > @@ -1103,11 +1116,11 @@ static struct tcp_md5sig_key *tcp_md5_do_lookup_exact(const struct sock *sk,
> >   #endif
> >   	hlist_for_each_entry_rcu(key, &md5sig->head, node,
> >   				 lockdep_sock_is_held(sk)) {
> >   		if (key->family != family)
> >   			continue;
> > -		if (key->l3index && key->l3index != l3index)
> > +		if (key->l3index != l3index)
>
> That seems like the bug fix there. The L3 reference needs to match for
> new key and existing key. I think the same change is needed in
> __tcp_md5_do_lookup.

Current behavior is that keys added without tcpm_ifindex will match 
connections both inside and outside VRFs. Changing this might break real 
applications, is it really OK to claim that this behavior was a bug all 
along?

The approach with most backward compatibility would be to add a new flag 
for keys that only match non-vrf connections.

Alternatively (TCP_MD5SIG_FLAG_IFINDEX && tcpm_ifindex == 0) could be 
defined as "only non-vrf connections" while TCP_MD5SIG_FLAG_IFINDEX 
missing could be "either".

--
Regards,
Leonard