[PATCH v12 net-next 14/23] net/tcp: Add TCP-AO SNE support

From: Dmitry Safonov
Date: Mon Sep 18 2023 - 15:01:59 EST

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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>
Acked-by: David Ahern <dsahern@xxxxxxxxxx>
---
include/net/tcp_ao.h | 22 ++++++++++++++++++++-
net/ipv4/tcp_ao.c | 41 ++++++++++++++++++++++++++++++++--------
net/ipv4/tcp_input.c | 28 +++++++++++++++++++++++++++
net/ipv4/tcp_ipv4.c | 3 ++-
net/ipv4/tcp_minisocks.c | 15 ++++++++++++++-
net/ipv4/tcp_output.c | 6 +++++-
net/ipv6/tcp_ipv6.c | 3 ++-
7 files changed, 105 insertions(+), 13 deletions(-)

diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index ec9a247f58cb..e62452bc17d6 100644
--- a/include/net/tcp_ao.h
+++ b/include/net/tcp_ao.h
@@ -95,6 +95,25 @@ 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;
};
@@ -145,6 +164,7 @@ 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);
@@ -154,7 +174,7 @@ int tcp_ao_hash_hdr(unsigned short family, char *ao_hash,
const union tcp_ao_addr *saddr,
const struct tcphdr *th, u32 sne);
int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
- const struct tcp_ao_hdr *aoh, int l3index,
+ const struct tcp_ao_hdr *aoh, int l3index, u32 seq,
struct tcp_ao_key **key, char **traffic_key,
bool *allocated_traffic_key, u8 *keyid, u32 *sne);

diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index ec636a8ecf33..0b5621cbc744 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -401,6 +401,21 @@ 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
@@ -611,7 +626,7 @@ struct tcp_ao_key *tcp_v4_ao_lookup(const struct sock *sk, struct sock *addr_sk,
}

int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
- const struct tcp_ao_hdr *aoh, int l3index,
+ const struct tcp_ao_hdr *aoh, int l3index, u32 seq,
struct tcp_ao_key **key, char **traffic_key,
bool *allocated_traffic_key, u8 *keyid, u32 *sne)
{
@@ -639,7 +654,7 @@ 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, seq);
} else {
sisn = th->seq;
disn = 0;
@@ -671,11 +686,15 @@ 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;

@@ -685,7 +704,8 @@ 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, seq);
}
return 0;
}
@@ -814,7 +834,8 @@ 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,
@@ -849,14 +870,16 @@ 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;
@@ -955,6 +978,7 @@ 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);
@@ -973,6 +997,7 @@ 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 92b89eda27a1..08b406cf989e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3546,9 +3546,18 @@ 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;
}

@@ -3556,9 +3565,18 @@ 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);
}

@@ -6414,6 +6432,16 @@ 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 c00c5573937f..b6af893d4679 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -675,7 +675,7 @@ static bool tcp_v4_ao_sign_reset(const struct sock *sk, struct sk_buff *skb,
u8 keyid;

rcu_read_lock();
- if (tcp_ao_prepare_reset(sk, skb, aoh, l3index,
+ if (tcp_ao_prepare_reset(sk, skb, aoh, l3index, ntohl(reply->seq),
&key, &traffic_key, &allocated_traffic_key,
&keyid, &ao_sne))
goto out;
@@ -1033,6 +1033,7 @@ static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb)
struct tcp_ao_key *rnext_key;

key.traffic_key = snd_other_key(key.ao_key);
+ key.sne = READ_ONCE(ao_info->snd_sne);
rnext_key = READ_ONCE(ao_info->rnext_key);
key.rcv_next = rnext_key->rcvid;
key.type = TCP_KEY_AO;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 8dd5de8188d1..49428a17174e 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 42bdc1b0c68b..d9f4c2336c66 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1411,6 +1411,7 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
void *tkey_buf = NULL;
u8 *traffic_key;
__be32 disn;
+ u32 sne;

ao = rcu_dereference_protected(tcp_sk(sk)->ao_info,
lockdep_sock_is_held(sk));
@@ -1432,9 +1433,12 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
} else {
traffic_key = snd_other_key(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, key.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 ba5130e0cb92..4e9131fd4233 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1087,7 +1087,7 @@ static void tcp_v6_send_reset(const struct sock *sk, struct sk_buff *skb)
int l3index;

l3index = tcp_v6_sdif(skb) ? tcp_v6_iif_l3_slave(skb) : 0;
- if (tcp_ao_prepare_reset(sk, skb, aoh, l3index,
+ if (tcp_ao_prepare_reset(sk, skb, aoh, l3index, seq,
&key.ao_key, &key.traffic_key,
&allocated_traffic_key,
&key.rcv_next, &key.sne))
@@ -1164,6 +1164,7 @@ 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);
key.rcv_next = rnext_key->rcvid;
+ key.sne = READ_ONCE(ao_info->snd_sne);
key.type = TCP_KEY_AO;
#else
if (0) {
--
2.41.0

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