[PATCH v10 net-next 11/23] net/tcp: Sign SYN-ACK segments with TCP-AO

From: Dmitry Safonov
Date: Tue Aug 15 2023 - 15:16:26 EST

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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@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.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 710d75b23b77..97fbe14a1275 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2180,6 +2180,9 @@ 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 409646be90c3..ead52113591e 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 94ca87240c17..a3f26a2ab690 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 968692f76fa2..c7487f30af42 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1676,6 +1676,7 @@ 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 a9e45b13720f..72c0c0746ce4 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;
@@ -3720,6 +3729,7 @@ 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;
@@ -3770,16 +3780,43 @@ 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);
+ kfree_skb(skb);
+ net_warn_ratelimited("TCP-AO: the keyid %u with maclen %u|%u from SYN packet is not present - not sending SYNACK\n",
+ keyid, maclen,
+ ao_key ? tcp_ao_maclen(ao_key) : 0);
+ 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);
@@ -3799,7 +3836,7 @@ 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);

@@ -3807,7 +3844,15 @@ 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 7178e8bab922..016871c6520f 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

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