[PATCH v8.1 net-next 14/23] net/tcp: Add TCP-AO SNE support
From: Dmitry Safonov
Date: Fri Jul 21 2023 - 12:23:16 EST
Add Sequence Number Extension (SNE) for TCP-AO.
This is needed to protect long-living TCP-AO connections from replaying
attacks after sequence number roll-over, see RFC5925 (6.2).
Co-developed-by: Francesco Ruggeri <fruggeri@xxxxxxxxxx>
Signed-off-by: Francesco Ruggeri <fruggeri@xxxxxxxxxx>
Co-developed-by: Salam Noureddine <noureddine@xxxxxxxxxx>
Signed-off-by: Salam Noureddine <noureddine@xxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
---
include/net/tcp_ao.h | 20 ++++++++++++++++++++
net/ipv4/tcp_ao.c | 40 +++++++++++++++++++++++++++++++++-------
net/ipv4/tcp_input.c | 28 ++++++++++++++++++++++++++++
net/ipv4/tcp_ipv4.c | 1 +
net/ipv4/tcp_minisocks.c | 15 ++++++++++++++-
net/ipv4/tcp_output.c | 6 +++++-
net/ipv6/tcp_ipv6.c | 1 +
7 files changed, 102 insertions(+), 9 deletions(-)
diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index 0a02098bddeb..fc5674763730 100644
--- a/include/net/tcp_ao.h
+++ b/include/net/tcp_ao.h
@@ -96,6 +96,25 @@ struct tcp_ao_info {
__unused :31;
__be32 lisn;
__be32 risn;
+ /* Sequence Number Extension (SNE) are upper 4 bytes for SEQ,
+ * that protect TCP-AO connection from replayed old TCP segments.
+ * See RFC5925 (6.2).
+ * In order to get correct SNE, there's a helper tcp_ao_compute_sne().
+ * It needs SEQ basis to understand whereabouts are lower SEQ numbers.
+ * According to that basis vector, it can provide incremented SNE
+ * when SEQ rolls over or provide decremented SNE when there's
+ * a retransmitted segment from before-rolling over.
+ * - for request sockets such basis is rcv_isn/snt_isn, which seems
+ * good enough as it's unexpected to receive 4 Gbytes on reqsk.
+ * - for full sockets the basis is rcv_nxt/snd_una. snd_una is
+ * taken instead of snd_nxt as currently it's easier to track
+ * in tcp_snd_una_update(), rather than updating SNE in all
+ * WRITE_ONCE(tp->snd_nxt, ...)
+ * - for time-wait sockets the basis is tw_rcv_nxt/tw_snd_nxt.
+ * tw_snd_nxt is not expected to change, while tw_rcv_nxt may.
+ */
+ u32 snd_sne;
+ u32 rcv_sne;
atomic_t refcnt; /* Protects twsk destruction */
struct rcu_head rcu;
};
@@ -144,6 +163,7 @@ enum skb_drop_reason tcp_inbound_ao_hash(struct sock *sk,
const struct sk_buff *skb, unsigned short int family,
const struct request_sock *req,
const struct tcp_ao_hdr *aoh);
+u32 tcp_ao_compute_sne(u32 next_sne, u32 next_seq, u32 seq);
struct tcp_ao_key *tcp_ao_do_lookup(const struct sock *sk,
const union tcp_ao_addr *addr,
int family, int sndid, int rcvid, u16 port);
diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index 5ab66928a952..5ebbfadfbfd0 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -403,6 +403,21 @@ static int tcp_ao_hash_pseudoheader(unsigned short int family,
return -EAFNOSUPPORT;
}
+u32 tcp_ao_compute_sne(u32 next_sne, u32 next_seq, u32 seq)
+{
+ u32 sne = next_sne;
+
+ if (before(seq, next_seq)) {
+ if (seq > next_seq)
+ sne--;
+ } else {
+ if (seq < next_seq)
+ sne++;
+ }
+
+ return sne;
+}
+
/* tcp_ao_hash_sne(struct tcp_sigpool *hp)
* @hp - used for hashing
* @sne - sne value
@@ -641,7 +656,8 @@ int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
sisn = htonl(tcp_rsk(req)->rcv_isn);
disn = htonl(tcp_rsk(req)->snt_isn);
- *sne = 0;
+ *sne = tcp_ao_compute_sne(0, tcp_rsk(req)->snt_isn,
+ ntohl(seq));
} else {
sisn = th->seq;
disn = 0;
@@ -674,11 +690,15 @@ int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
*keyid = (*key)->rcvid;
} else {
struct tcp_ao_key *rnext_key;
+ u32 snd_basis;
- if (sk->sk_state == TCP_TIME_WAIT)
+ if (sk->sk_state == TCP_TIME_WAIT) {
ao_info = rcu_dereference(tcp_twsk(sk)->ao_info);
- else
+ snd_basis = tcp_twsk(sk)->tw_snd_nxt;
+ } else {
ao_info = rcu_dereference(tcp_sk(sk)->ao_info);
+ snd_basis = tcp_sk(sk)->snd_una;
+ }
if (!ao_info)
return -ENOENT;
@@ -688,7 +708,8 @@ int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
*traffic_key = snd_other_key(*key);
rnext_key = READ_ONCE(ao_info->rnext_key);
*keyid = rnext_key->rcvid;
- *sne = 0;
+ *sne = tcp_ao_compute_sne(READ_ONCE(ao_info->snd_sne),
+ snd_basis, ntohl(seq));
}
return 0;
}
@@ -821,7 +842,8 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
if (unlikely(th->syn && !th->ack))
goto verify_hash;
- sne = 0;
+ sne = tcp_ao_compute_sne(info->rcv_sne, tcp_sk(sk)->rcv_nxt,
+ ntohl(th->seq));
/* Established socket, traffic key are cached */
traffic_key = rcv_other_key(key);
err = tcp_ao_verify_hash(sk, skb, family, info, aoh, key,
@@ -856,14 +878,16 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV)) {
/* Make the initial syn the likely case here */
if (unlikely(req)) {
- sne = 0;
+ sne = tcp_ao_compute_sne(0, tcp_rsk(req)->rcv_isn,
+ ntohl(th->seq));
sisn = htonl(tcp_rsk(req)->rcv_isn);
disn = htonl(tcp_rsk(req)->snt_isn);
} else if (unlikely(th->ack && !th->syn)) {
/* Possible syncookie packet */
sisn = htonl(ntohl(th->seq) - 1);
disn = htonl(ntohl(th->ack_seq) - 1);
- sne = 0;
+ sne = tcp_ao_compute_sne(0, ntohl(sisn),
+ ntohl(th->seq));
} else if (unlikely(!th->syn)) {
/* no way to figure out initial sisn/disn - drop */
return SKB_DROP_REASON_TCP_FLAGS;
@@ -963,6 +987,7 @@ void tcp_ao_connect_init(struct sock *sk)
tp->tcp_header_len += tcp_ao_len(key);
ao_info->lisn = htonl(tp->write_seq);
+ ao_info->snd_sne = 0;
} else {
/* TODO: probably, it should fail to connect() here */
rcu_assign_pointer(tp->ao_info, NULL);
@@ -981,6 +1006,7 @@ void tcp_ao_finish_connect(struct sock *sk, struct sk_buff *skb)
return;
ao->risn = tcp_hdr(skb)->seq;
+ ao->rcv_sne = 0;
hlist_for_each_entry_rcu(key, &ao->head, node)
tcp_ao_cache_traffic_keys(sk, ao, key);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2a7ed329f7cb..4b37e82ab612 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3532,9 +3532,18 @@ static inline bool tcp_may_update_window(const struct tcp_sock *tp,
static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
{
u32 delta = ack - tp->snd_una;
+#ifdef CONFIG_TCP_AO
+ struct tcp_ao_info *ao;
+#endif
sock_owned_by_me((struct sock *)tp);
tp->bytes_acked += delta;
+#ifdef CONFIG_TCP_AO
+ ao = rcu_dereference_protected(tp->ao_info,
+ lockdep_sock_is_held((struct sock *)tp));
+ if (ao && ack < tp->snd_una)
+ ao->snd_sne++;
+#endif
tp->snd_una = ack;
}
@@ -3542,9 +3551,18 @@ static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
{
u32 delta = seq - tp->rcv_nxt;
+#ifdef CONFIG_TCP_AO
+ struct tcp_ao_info *ao;
+#endif
sock_owned_by_me((struct sock *)tp);
tp->bytes_received += delta;
+#ifdef CONFIG_TCP_AO
+ ao = rcu_dereference_protected(tp->ao_info,
+ lockdep_sock_is_held((struct sock *)tp));
+ if (ao && seq < tp->rcv_nxt)
+ ao->rcv_sne++;
+#endif
WRITE_ONCE(tp->rcv_nxt, seq);
}
@@ -6387,6 +6405,16 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
* simultaneous connect with crossed SYNs.
* Particularly, it can be connect to self.
*/
+#ifdef CONFIG_TCP_AO
+ struct tcp_ao_info *ao;
+
+ ao = rcu_dereference_protected(tp->ao_info,
+ lockdep_sock_is_held(sk));
+ if (ao) {
+ ao->risn = th->seq;
+ ao->rcv_sne = 0;
+ }
+#endif
tcp_set_state(sk, TCP_SYN_RECV);
if (tp->rx_opt.saw_tstamp) {
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index d8d2499b5e26..37497dec5eb9 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1039,6 +1039,7 @@ static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb)
struct tcp_ao_key *rnext_key;
traffic_key = snd_other_key(ao_key);
+ ao_sne = READ_ONCE(ao_info->snd_sne);
rnext_key = READ_ONCE(ao_info->rnext_key);
rcv_next = rnext_key->rcvid;
}
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 11b76fa601a7..3b367365dc7d 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -51,6 +51,18 @@ tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
return TCP_TW_SUCCESS;
}
+static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq)
+{
+#ifdef CONFIG_TCP_AO
+ struct tcp_ao_info *ao;
+
+ ao = rcu_dereference(tcptw->ao_info);
+ if (unlikely(ao && seq < tcptw->tw_rcv_nxt))
+ WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1);
+#endif
+ tcptw->tw_rcv_nxt = seq;
+}
+
/*
* * Main purpose of TIME-WAIT state is to close connection gracefully,
* when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
@@ -136,7 +148,8 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
/* FIN arrived, enter true time-wait state. */
tw->tw_substate = TCP_TIME_WAIT;
- tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq);
+
if (tmp_opt.saw_tstamp) {
tcptw->tw_ts_recent_stamp = ktime_get_seconds();
tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ed1164f287b7..d87a3823fec5 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1443,6 +1443,7 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
u8 *traffic_key;
void *tkey_buf = NULL;
u32 disn;
+ u32 sne;
sk_gso_disable(sk);
if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
@@ -1460,9 +1461,12 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
} else {
traffic_key = snd_other_key(ao_key);
}
+ sne = tcp_ao_compute_sne(READ_ONCE(ao->snd_sne),
+ READ_ONCE(tp->snd_una),
+ ntohl(th->seq));
tp->af_specific->calc_ao_hash(opts.hash_location, ao_key, sk, skb,
traffic_key,
- opts.hash_location - (u8 *)th, 0);
+ opts.hash_location - (u8 *)th, sne);
kfree(tkey_buf);
}
#endif
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index c825d7c80f5b..873ce0d72f34 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1180,6 +1180,7 @@ static void tcp_v6_timewait_ack(struct sock *sk, struct sk_buff *skb)
/* rcv_next switches to our rcv_next */
rnext_key = READ_ONCE(ao_info->rnext_key);
rcv_next = rnext_key->rcvid;
+ ao_sne = READ_ONCE(ao_info->snd_sne);
}
#endif
--
2.41.0