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

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Date:   Thu, 7 Oct 2021 09:41:42 +0300
From:   Leonard Crestez <cdleonard@...il.com>
To:     David Ahern <dsahern@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Ahern <dsahern@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        Yonghong Song <yhs@...com>,
        Alexander Duyck <alexanderduyck@...com>,
        Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: md5: Fix overlap between vrf and non-vrf keys



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