Similarly to RST segments, wire SYN-ACKs to TCP-AO.
tcp_rsk_used_ao() is handy here to check if the request socket used AO
and needs a signature on the outgoing segments.

Co-developed-by: Francesco Ruggeri <redacted>
Signed-off-by: Francesco Ruggeri <redacted>
Co-developed-by: Salam Noureddine <redacted>
Signed-off-by: Salam Noureddine <redacted>
Signed-off-by: Dmitry Safonov <redacted>
Acked-by: David Ahern <dsahern@kernel.org>
---
 include/net/tcp.h     |  3 +++
 include/net/tcp_ao.h  |  6 +++++
 net/ipv4/tcp_ao.c     | 22 +++++++++++++++++
 net/ipv4/tcp_ipv4.c   |  1 +
 net/ipv4/tcp_output.c | 57 ++++++++++++++++++++++++++++++++++++++-----
 net/ipv6/tcp_ao.c     | 22 +++++++++++++++++
 net/ipv6/tcp_ipv6.c   |  1 +
 7 files changed, 106 insertions(+), 6 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 5daa2e98e6a3..56f4180443c7 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h

@@ -2179,6 +2179,9 @@ struct tcp_request_sock_ops {
                                        struct request_sock *req,
                                        int sndid, int rcvid);
        int (*ao_calc_key)(struct tcp_ao_key *mkt, u8 *key, struct request_sock *sk);
+       int (*ao_synack_hash)(char *ao_hash, struct tcp_ao_key *mkt,
+                             struct request_sock *req, const struct sk_buff *skb,
+                             int hash_offset, u32 sne);
 #endif
 #ifdef CONFIG_SYN_COOKIES
        __u32 (*cookie_init_seq)(const struct sk_buff *skb,

diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index d26d98f1b048..c922d2e31d08 100644
--- a/include/net/tcp_ao.h
+++ b/include/net/tcp_ao.h

@@ -144,6 +144,9 @@ int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
 int tcp_v4_parse_ao(struct sock *sk, int cmd, sockptr_t optval, int optlen);
 struct tcp_ao_key *tcp_v4_ao_lookup(const struct sock *sk, struct sock *addr_sk,
                                    int sndid, int rcvid);
+int tcp_v4_ao_synack_hash(char *ao_hash, struct tcp_ao_key *mkt,
+                         struct request_sock *req, const struct sk_buff *skb,
+                         int hash_offset, u32 sne);
 int tcp_v4_ao_calc_key_sk(struct tcp_ao_key *mkt, u8 *key,
                          const struct sock *sk,
                          __be32 sisn, __be32 disn, bool send);

@@ -178,6 +181,9 @@ int tcp_v6_ao_hash_skb(char *ao_hash, struct tcp_ao_key *key,
                       const struct sock *sk, const struct sk_buff *skb,
                       const u8 *tkey, int hash_offset, u32 sne);
 int tcp_v6_parse_ao(struct sock *sk, int cmd, sockptr_t optval, int optlen);
+int tcp_v6_ao_synack_hash(char *ao_hash, struct tcp_ao_key *ao_key,
+                         struct request_sock *req, const struct sk_buff *skb,
+                         int hash_offset, u32 sne);
 void tcp_ao_finish_connect(struct sock *sk, struct sk_buff *skb);
 void tcp_ao_connect_init(struct sock *sk);
 void tcp_ao_syncookie(struct sock *sk, const struct sk_buff *skb,

diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index b114f3d901a0..0d8ea381300b 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c

@@ -568,6 +568,28 @@ int tcp_v4_ao_hash_skb(char *ao_hash, struct tcp_ao_key *key,
                               tkey, hash_offset, sne);
 }

+int tcp_v4_ao_synack_hash(char *ao_hash, struct tcp_ao_key *ao_key,
+                         struct request_sock *req, const struct sk_buff *skb,
+                         int hash_offset, u32 sne)
+{
+       void *hash_buf = NULL;
+       int err;
+
+       hash_buf = kmalloc(tcp_ao_digest_size(ao_key), GFP_ATOMIC);
+       if (!hash_buf)
+               return -ENOMEM;
+
+       err = tcp_v4_ao_calc_key_rsk(ao_key, hash_buf, req);
+       if (err)
+               goto out;
+
+       err = tcp_ao_hash_skb(AF_INET, ao_hash, ao_key, req_to_sk(req), skb,
+                             hash_buf, hash_offset, sne);
+out:
+       kfree(hash_buf);
+       return err;
+}
+
 struct tcp_ao_key *tcp_v4_ao_lookup_rsk(const struct sock *sk,
                                        struct request_sock *req,
                                        int sndid, int rcvid)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 9a4ffcc965f3..c40da33d988b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c

@@ -1675,6 +1675,7 @@ const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {
 #ifdef CONFIG_TCP_AO
        .ao_lookup      =       tcp_v4_ao_lookup_rsk,
        .ao_calc_key    =       tcp_v4_ao_calc_key_rsk,
+       .ao_synack_hash =       tcp_v4_ao_synack_hash,
 #endif
 #ifdef CONFIG_SYN_COOKIES
        .cookie_init_seq =      cookie_v4_init_sequence,

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 44c97e6ddd50..c9d6decef443 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c

@@ -900,6 +900,7 @@ static unsigned int tcp_synack_options(const struct sock *sk,
                                       unsigned int mss, struct sk_buff *skb,
                                       struct tcp_out_options *opts,
                                       const struct tcp_md5sig_key *md5,
+                                      const struct tcp_ao_key *ao,
                                       struct tcp_fastopen_cookie *foc,
                                       enum tcp_synack_type synack_type,
                                       struct sk_buff *syn_skb)

@@ -921,6 +922,14 @@ static unsigned int tcp_synack_options(const struct sock *sk,
                        ireq->tstamp_ok &= !ireq->sack_ok;
        }
 #endif
+#ifdef CONFIG_TCP_AO
+       if (ao) {
+               opts->options |= OPTION_AO;
+               remaining -= tcp_ao_len(ao);
+               ireq->tstamp_ok &= !ireq->sack_ok;
+       }
+#endif
+       WARN_ON_ONCE(md5 && ao);

        /* We always send an MSS option. */
        opts->mss = mss;

@@ -3727,6 +3736,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
        struct inet_request_sock *ireq = inet_rsk(req);
        const struct tcp_sock *tp = tcp_sk(sk);
        struct tcp_md5sig_key *md5 = NULL;
+       struct tcp_ao_key *ao_key = NULL;
        struct tcp_out_options opts;
        struct sk_buff *skb;
        int tcp_header_size;

@@ -3777,16 +3787,43 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
                        tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);
        }

-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
        rcu_read_lock();
-       md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
 #endif
+       if (tcp_rsk_used_ao(req)) {
+#ifdef CONFIG_TCP_AO
+               u8 maclen = tcp_rsk(req)->maclen;
+               u8 keyid = tcp_rsk(req)->ao_keyid;
+
+               ao_key = tcp_sk(sk)->af_specific->ao_lookup(sk, req_to_sk(req),
+                                                           keyid, -1);
+               /* If there is no matching key - avoid sending anything,
+                * especially usigned segments. It could try harder and lookup
+                * for another peer-matching key, but the peer has requested
+                * ao_keyid (RFC5925 RNextKeyID), so let's keep it simple here.
+                */
+               if (unlikely(!ao_key || tcp_ao_maclen(ao_key) != maclen)) {
+                       rcu_read_unlock();
+                       skb_dst_drop(skb);

+                       return NULL;
+               }
+#endif
+       } else {
+#ifdef CONFIG_TCP_MD5SIG
+               md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk,
+                                                               req_to_sk(req));
+#endif
+       }
        skb_set_hash(skb, READ_ONCE(tcp_rsk(req)->txhash), PKT_HASH_TYPE_L4);
        /* bpf program will be interested in the tcp_flags */
        TCP_SKB_CB(skb)->tcp_flags = TCPHDR_SYN | TCPHDR_ACK;
        tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5,
-                                            foc, synack_type,
-                                            syn_skb) + sizeof(*th);
+                                            ao_key, foc, synack_type, syn_skb)
+                                       + sizeof(*th);

        skb_push(skb, tcp_header_size);
        skb_reset_transport_header(skb);

@@ -3806,7 +3843,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,

        /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
        th->window = htons(min(req->rsk_rcv_wnd, 65535U));
-       tcp_options_write(th, NULL, NULL, &opts, NULL);
+       tcp_options_write(th, NULL, tcp_rsk(req), &opts, ao_key);
        th->doff = (tcp_header_size >> 2);
        TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);

@@ -3814,7 +3851,15 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
        /* Okay, we have all we need - do the md5 hash if needed */
        if (md5)
                tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
-                                              md5, req_to_sk(req), skb);
+                                       md5, req_to_sk(req), skb);
+#endif
+#ifdef CONFIG_TCP_AO
+       if (ao_key)
+               tcp_rsk(req)->af_specific->ao_synack_hash(opts.hash_location,
+                                       ao_key, req, skb,
+                                       opts.hash_location - (u8 *)th, 0);
+#endif
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
        rcu_read_unlock();
 #endif

diff --git a/net/ipv6/tcp_ao.c b/net/ipv6/tcp_ao.c
index c9a6fa84f6ce..99753e12c08c 100644
--- a/net/ipv6/tcp_ao.c
+++ b/net/ipv6/tcp_ao.c

@@ -144,3 +144,25 @@ int tcp_v6_parse_ao(struct sock *sk, int cmd,
 {
        return tcp_parse_ao(sk, cmd, AF_INET6, optval, optlen);
 }
+
+int tcp_v6_ao_synack_hash(char *ao_hash, struct tcp_ao_key *ao_key,
+                         struct request_sock *req, const struct sk_buff *skb,
+                         int hash_offset, u32 sne)
+{
+       void *hash_buf = NULL;
+       int err;
+
+       hash_buf = kmalloc(tcp_ao_digest_size(ao_key), GFP_ATOMIC);
+       if (!hash_buf)
+               return -ENOMEM;
+
+       err = tcp_v6_ao_calc_key_rsk(ao_key, hash_buf, req);
+       if (err)
+               goto out;
+
+       err = tcp_ao_hash_skb(AF_INET6, ao_hash, ao_key, req_to_sk(req), skb,
+                             hash_buf, hash_offset, sne);
+out:
+       kfree(hash_buf);
+       return err;
+}

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index c060cd964f91..f57617d2921a 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c

@@ -845,6 +845,7 @@ const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = {
 #ifdef CONFIG_TCP_AO
        .ao_lookup      =       tcp_v6_ao_lookup_rsk,
        .ao_calc_key    =       tcp_v6_ao_calc_key_rsk,
+       .ao_synack_hash =       tcp_v6_ao_synack_hash,
 #endif
 #ifdef CONFIG_SYN_COOKIES
        .cookie_init_seq =      cookie_v6_init_sequence,
--

2.41.0