Re: [PATCH v8 01/26] tcp: authopt: Initial support and key management

[Leonard Crestez]

On 9/7/22 01:57, Eric Dumazet wrote:
> On Mon, Sep 5, 2022 at 12:06 AM Leonard Crestez <cdleonard@xxxxxxxxx> wrote:
> > This commit adds support to add and remove keys but does not use them
> > further.
> >
> > Similar to tcp md5 a single pointer to a struct tcp_authopt_info* struct
> > is added to struct tcp_sock, this avoids increasing memory usage. The
> > data structures related to tcp_authopt are initialized on setsockopt and
> > only freed on socket close.
>
> Thanks Leonard.
>
> Small points from my side, please find them attached.

...

> > +/* Free info and keys.
> > + * Don't touch tp->authopt_info, it might not even be assigned yes.
> > + */
> > +void tcp_authopt_free(struct sock *sk, struct tcp_authopt_info *info)
> > +{
> > +       kfree_rcu(info, rcu);
> > +}
> > +
> > +/* Free everything and clear tcp_sock.authopt_info to NULL */
> > +void tcp_authopt_clear(struct sock *sk)
> > +{
> > +       struct tcp_authopt_info *info;
> > +
> > +       info = rcu_dereference_protected(tcp_sk(sk)->authopt_info, lockdep_sock_is_held(sk));
> > +       if (info) {
> > +               tcp_authopt_free(sk, info);
> > +               tcp_sk(sk)->authopt_info = NULL;
>
> RCU rules at deletion mandate that the pointer must be cleared before
> the call_rcu()/kfree_rcu() call.
>
> It is possible that current MD5 code has an issue here, let's not copy/paste it.

OK. Is there a need for some special form of assignment or is current 
plain form enough?

> > +       }
> > +}
> > +
> > +/* checks that ipv4 or ipv6 addr matches. */
> > +static bool ipvx_addr_match(struct sockaddr_storage *a1,
> > +                           struct sockaddr_storage *a2)
> > +{
> > +       if (a1->ss_family != a2->ss_family)
> > +               return false;
> > +       if (a1->ss_family == AF_INET &&
> > +           (((struct sockaddr_in *)a1)->sin_addr.s_addr !=
> > +            ((struct sockaddr_in *)a2)->sin_addr.s_addr))
> > +               return false;
> > +       if (a1->ss_family == AF_INET6 &&
> > +           !ipv6_addr_equal(&((struct sockaddr_in6 *)a1)->sin6_addr,
> > +                            &((struct sockaddr_in6 *)a2)->sin6_addr))
> > +               return false;
> > +       return true;
> > +}
>
> Always surprising to see this kind of generic helper being added in a patch.

I remember looking for an equivalent and not finding it. Many places 
have distinct code paths for ipv4 and ipv6 and my use of 
"sockaddr_storage" as ipv4/ipv6 union is uncommon.

It also wastes some memory.

> > +int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *opt)
> > +{
> > +       struct tcp_sock *tp = tcp_sk(sk);
> > +       struct tcp_authopt_info *info;
> > +
> > +       memset(opt, 0, sizeof(*opt));
> > +       sock_owned_by_me(sk);
> > +
> > +       info = rcu_dereference_check(tp->authopt_info, lockdep_sock_is_held(sk));
>
> Probably not a big deal, but it seems the prior sock_owned_by_me()
> might be redundant.

The sock_owned_by_me call checks checks lockdep_sock_is_held

The rcu_dereference_check call checks lockdep_sock_is_held || 
rcu_read_lock_held()

This is a getsockopt so caller ensures socket locking but 
rcu_read_lock_held() == 0.

The sock_owned_by_me is indeed redundant because it seems very unlikely 
the sockopt calling conditions will be changes. It was mostly there to 
clarify for myself because I had probably at one time with locking 
warnings. I guess they can be removed.

> > +int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
> > +{
> > +       struct tcp_authopt_key opt;
> > +       struct tcp_authopt_info *info;
> > +       struct tcp_authopt_key_info *key_info, *old_key_info;
> > +       struct netns_tcp_authopt *net = sock_net_tcp_authopt(sk);
> > +       int err;
> > +
> > +       sock_owned_by_me(sk);
> > +       if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
> > +               return -EPERM;
> > +
> > +       err = _copy_from_sockptr_tolerant((u8 *)&opt, sizeof(opt), optval, optlen);
> > +       if (err)
> > +               return err;
> > +
> > +       if (opt.flags & ~TCP_AUTHOPT_KEY_KNOWN_FLAGS)
> > +               return -EINVAL;
> > +
> > +       if (opt.keylen > TCP_AUTHOPT_MAXKEYLEN)
> > +               return -EINVAL;
> > +
> > +       /* Delete is a special case: */
> > +       if (opt.flags & TCP_AUTHOPT_KEY_DEL) {
> > +               mutex_lock(&net->mutex);
> > +               key_info = tcp_authopt_key_lookup_exact(sk, net, &opt);
> > +               if (key_info) {
> > +                       tcp_authopt_key_del(net, key_info);
> > +                       err = 0;
> > +               } else {
> > +                       err = -ENOENT;
> > +               }
> > +               mutex_unlock(&net->mutex);
> > +               return err;
> > +       }
> > +
> > +       /* check key family */
> > +       if (opt.flags & TCP_AUTHOPT_KEY_ADDR_BIND) {
> > +               if (sk->sk_family != opt.addr.ss_family)
> > +                       return -EINVAL;
> > +       }
> > +
> > +       /* Initialize tcp_authopt_info if not already set */
> > +       info = __tcp_authopt_info_get_or_create(sk);
> > +       if (IS_ERR(info))
> > +               return PTR_ERR(info);
> > +
> > +       key_info = kmalloc(sizeof(*key_info), GFP_KERNEL | __GFP_ZERO);
>
> kzalloc() ?

Yes

> > +static int tcp_authopt_init_net(struct net *full_net)
>
> Hmmm... our convention is to use "struct net *net"
>
> > +{
> > +       struct netns_tcp_authopt *net = &full_net->tcp_authopt;
>
> Here, you should use a different name ...

OK, will replace with net_ao

> > @@ -2267,10 +2268,11 @@ void tcp_v4_destroy_sock(struct sock *sk)
> >                  tcp_clear_md5_list(sk);
> >                  kfree_rcu(rcu_dereference_protected(tp->md5sig_info, 1), rcu);
> >                  tp->md5sig_info = NULL;
> >          }
> >   #endif
> > +       tcp_authopt_clear(sk);
>
> Do we really own the socket lock at this point ?

Not sure how I would tell but there is a lockdep_sock_is_held check 
inside tcp_authopt_clear. I also added sock_owned_by_me and there were 
no warnings.