On Thu, Dec 1, 2022 at 8:38 PM Eric Dumazet [off-list ref] wrote:

On Wed, Nov 23, 2022 at 6:39 PM Dmitry Safonov [off-list ref] wrote:

quoted

To do that, separate two scenarios:
- where it's the first MD5 key on the system, which means that enabling
  of the static key may need to sleep;
- copying of an existing key from a listening socket to the request
  socket upon receiving a signed TCP segment, where static key was
  already enabled (when the key was added to the listening socket).

Now the life-time of the static branch for TCP-MD5 is until:
- last tcp_md5sig_info is destroyed
- last socket in time-wait state with MD5 key is closed.

Which means that after all sockets with TCP-MD5 keys are gone, the
system gets back the performance of disabled md5-key static branch.

While at here, provide static_key_fast_inc() helper that does ref
counter increment in atomic fashion (without grabbing cpus_read_lock()
on CONFIG_JUMP_LABEL=y). This is needed to add a new user for
a static_key when the caller controls the lifetime of another user.

Signed-off-by: Dmitry Safonov <redacted>
Acked-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Hmm, I missed two kfree_rcu(key) calls, I will send the following fix:

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 7fae586405cfb10011a0674289280bf400dfa8d8..8320d0ecb13ae1e3e259f3c13a4c2797fbd984a5

100644

--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c

@@ -1245,7 +1245,7 @@ int tcp_md5_do_add(struct sock *sk, const union

tcp_md5_addr *addr,

                        md5sig =
rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk));
                        rcu_assign_pointer(tp->md5sig_info, NULL);
-                       kfree_rcu(md5sig);
+                       kfree_rcu(md5sig, rcu);
                        return -EUSERS;
                }
        }

@@ -1271,7 +1271,7 @@ int tcp_md5_key_copy(struct sock *sk, const

union tcp_md5_addr *addr,
                        md5sig =
rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk));
                        net_warn_ratelimited("Too many TCP-MD5 keys in
the system\n");
                        rcu_assign_pointer(tp->md5sig_info, NULL);
-                       kfree_rcu(md5sig);
+                       kfree_rcu(md5sig, rcu);
                        return -EUSERS;
                }
        }