[PATCH v2 16/35] net/tcp: Sign SYN-ACK segments with TCP-AO

Dmitry Safonov
2022-09-23T20:15:18Z

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 <fruggeri@arista.com>
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Co-developed-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
include/net/tcp.h | 4 ++++
include/net/tcp_ao.h | 6 ++++++
net/ipv4/tcp_ao.c | 14 ++++++++++++++
net/ipv4/tcp_ipv4.c | 1 +
net/ipv4/tcp_output.c | 37 +++++++++++++++++++++++++++++++------
net/ipv6/tcp_ao.c | 14 ++++++++++++++
net/ipv6/tcp_ipv6.c | 1 +
7 files changed, 71 insertions(+), 6 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index f21898bb31bd..19549be29265 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2109,6 +2109,10 @@ struct tcp_request_sock_ops {
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 a1d26e1a0b82..cc3f6686d5c9 100644
--- a/include/net/tcp_ao.h
+++ b/include/net/tcp_ao.h
@@ -142,6 +142,9 @@ int tcp_ao_hash_hdr(unsigned short family, char *ao_hash,
int tcp_v4_parse_ao(struct sock *sk, int optname, 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);
@@ -176,6 +179,9 @@ int tcp_v6_ao_hash_skb(char *ao_hash, struct tcp_ao_key *key,
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);

diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index a90b950781f9..6a601279852d 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -603,6 +603,20 @@ 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)
+{
+ char traffic_key[TCP_AO_MAX_HASH_SIZE] __tcp_ao_key_align;
+
+ tcp_v4_ao_calc_key_rsk(ao_key, traffic_key, req);
+
+ tcp_ao_hash_skb(AF_INET, ao_hash, ao_key, req_to_sk(req), skb,
+ traffic_key, hash_offset, sne);
+
+ return 0;
+}
+
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 cbe428957686..fedccda1dd55 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1654,6 +1654,7 @@ 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 be92fe85e82c..c08ad98721d6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3632,6 +3632,7 @@ 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;
@@ -3682,16 +3683,32 @@ 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
+ /* TODO: what should we do if the key is no longer available on
+ * the listening socket? Maybe we can try a different matching
+ * key (without sndid match). If that also fails what should
+ * we do? We currently send an unsigned synack. It's probably
+ * better to not send anything.
+ */
+ ao_key = tcp_sk(sk)->af_specific->ao_lookup(sk, req_to_sk(req),
+ tcp_rsk(req)->ao_keyid, -1);
+#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, 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,
- NULL, 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);
@@ -3711,7 +3728,7 @@ 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, NULL);
th->doff = (tcp_header_size >> 2);
__TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);

@@ -3719,7 +3736,15 @@ 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 31ae504af8e6..526bbe232a64 100644
--- a/net/ipv6/tcp_ao.c
+++ b/net/ipv6/tcp_ao.c
@@ -123,3 +123,17 @@ 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)
+{
+ char traffic_key[TCP_AO_MAX_HASH_SIZE] __tcp_ao_key_align;
+
+ tcp_v6_ao_calc_key_rsk(ao_key, traffic_key, req);
+
+ tcp_ao_hash_skb(AF_INET6, ao_hash, ao_key, req_to_sk(req), skb,
+ traffic_key, hash_offset, sne);
+
+ return 0;
+}
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 7610fdf5d519..16cea7de0851 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -838,6 +838,7 @@ 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,
--
2.37.2