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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 2 Dec 2022 06:05:28 +0100
Message-ID: <CANn89i+6dKFvBRHNyfSbZ6e+Azjz-x48D1um0qrKVRw0xoUquA@mail.gmail.com>
Subject: Re: [PATCH v6 3/5] net/tcp: Disable TCP-MD5 static key on
 tcp_md5sig_info destruction
To:     Dmitry Safonov <dima@arista.com>
Cc:     linux-kernel@vger.kernel.org, David Ahern <dsahern@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Bob Gilligan <gilligan@arista.com>,
        "David S. Miller" <davem@davemloft.net>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Francesco Ruggeri <fruggeri@arista.com>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Jason Baron <jbaron@akamai.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Salam Noureddine <noureddine@arista.com>,
        Steven Rostedt <rostedt@goodmis.org>, netdev@vger.kernel.org
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On Thu, Dec 1, 2022 at 8:38 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Wed, Nov 23, 2022 at 6:39 PM Dmitry Safonov <dima@arista.com> wrote:
> >
> > 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 <dima@arista.com>
> > 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;
                }
        }