[PATCH v2 net-next 0/9] mptcp: add syncookie support

[PATCH v2 net-next 0/9] mptcp: add syncookie support

[Florian Westphal]

Changes in v2:
- first patch renames req->ts_cookie to req->syncookie instead of
  removing ts_cookie member.
- patch to add 'want_cookie' arg to init_req() functions has been dropped.
  All users of that arg were changed to check 'req->syncookie' instead.

v1 cover letter:

When syn-cookies are used the SYN?ACK never contains a MPTCP option,
because the code path that creates a request socket based on a valid
cookie ACK lacks the needed changes to construct MPTCP request sockets.

After this series, if SYN carries MP_CAPABLE option, the option is not
cleared anymore and request socket will be reconstructed using the
MP_CAPABLE option data that is re-sent with the ACK.

This means that no additional state gets encoded into the syn cookie or
the TCP timestamp.

There are two caveats for SYN-Cookies with MPTCP:

1. When syn-cookies are used, the server-generated key is not stored.
The drawback is that the next connection request that comes in before
the cookie-ACK has a small chance that it will generate the same local_key.

If this happens, the cookie ACK that comes in second will (re)compute the
token hash and then detects that this is already in use.
Unlike normal case, where the server will pick a new key value and then
re-tries, we can't do that because we already committed to the key value
(it was sent to peer already).

Im this case, MPTCP cannot be used and late TCP fallback happens.

2). SYN packets with a MP_JOIN requests cannot be handled without storing
    state. This is because the SYN contains a nonce value that is needed to
    verify the HMAC of the MP_JOIN ACK that completes the three-way
    handshake.  Also, a local nonce is generated and used in the cookie
    SYN/ACK.

There are only 2 ways to solve this:
 a) Do not support JOINs when cookies are in effect.
 b) Store the nonces somewhere.

The approach chosen here is b).
Patch 8 adds a fixed-size (1024 entries) state table to store the
information required to validate the MP_JOIN ACK and re-build the
request socket.

State gets stored when syn-cookies are active and the token in the JOIN
request referred to an established MPTCP connection that can also accept
a new subflow.

State is restored if the ACK cookie is valid, an MP_JOIN option is present
and the state slot contains valid data from a previous SYN.

After the request socket has been re-build, normal HMAC check is done just
as without syn cookies.

Largely identical to last RFC, except patch #8 which follows Paolos
suggestion to use a private table storage area rather than keeping
request sockets around.  This also means I dropped the patch to remove
const qualifier from sk_listener pointers.

Florian Westphal (9):
      tcp: rename request_sock cookie_ts bit to syncookie
      mptcp: token: move retry to caller
      mptcp: subflow: split subflow_init_req
      mptcp: rename and export mptcp_subflow_request_sock_ops
      mptcp: subflow: add mptcp_subflow_init_cookie_req helper
      tcp: syncookies: create mptcp request socket for ACK cookies with MPTCP option
      mptcp: enable JOIN requests even if cookies are in use
      selftests: mptcp: make 2nd net namespace use tcp syn cookies unconditionally
      selftests: mptcp: add test cases for mptcp join tests with syn cookies

 drivers/crypto/chelsio/chtls/chtls_cm.c            |   2 +-
 include/net/mptcp.h                                |  11 ++
 include/net/request_sock.h                         |   2 +-
 include/net/tcp.h                                  |   2 +
 net/ipv4/syncookies.c                              |  44 ++++++-
 net/ipv4/tcp_input.c                               |   6 +-
 net/ipv4/tcp_output.c                              |   2 +-
 net/ipv6/syncookies.c                              |   5 +-
 net/mptcp/Makefile                                 |   1 +
 net/mptcp/ctrl.c                                   |   1 +
 net/mptcp/protocol.h                               |  21 ++++
 net/mptcp/subflow.c                                | 116 +++++++++++++++---
 net/mptcp/syncookies.c                             | 132 +++++++++++++++++++++
 net/mptcp/token.c                                  |  38 ++++--
 tools/testing/selftests/net/mptcp/mptcp_connect.sh |  47 ++++++++
 tools/testing/selftests/net/mptcp/mptcp_join.sh    |  66 ++++++++++-
 16 files changed, 453 insertions(+), 43 deletions(-)
 create mode 100644 net/mptcp/syncookies.c

[PATCH v2 net-next 1/9] tcp: rename request_sock cookie_ts bit to syncookie

[Florian Westphal]

Nowadays output function has a 'synack_type' argument that tells us when
the syn/ack is emitted via syncookies.

The request already tells us when timestamps are supported, so check
both to detect special timestamp for tcp option encoding is needed.

We could remove cookie_ts altogether, but a followup patch would
otherwise need to adjust function signatures to pass 'want_cookie' to
mptcp core.

This way, the 'existing' bit can be used.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 drivers/crypto/chelsio/chtls/chtls_cm.c | 2 +-
 include/net/request_sock.h              | 2 +-
 net/ipv4/tcp_input.c                    | 3 +--
 net/ipv4/tcp_output.c                   | 2 +-
 4 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/crypto/chelsio/chtls/chtls_cm.c b/drivers/crypto/chelsio/chtls/chtls_cm.c
index f924c335a195..05520dccd906 100644
--- a/drivers/crypto/chelsio/chtls/chtls_cm.c
+++ b/drivers/crypto/chelsio/chtls/chtls_cm.c
@@ -1348,7 +1348,7 @@ static void chtls_pass_accept_request(struct sock *sk,
 
 	oreq->rsk_rcv_wnd = 0;
 	oreq->rsk_window_clamp = 0;
-	oreq->cookie_ts = 0;
+	oreq->syncookie = 0;
 	oreq->mss = 0;
 	oreq->ts_recent = 0;
 
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index cf8b33213bbc..b2eb8b4ba697 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -54,7 +54,7 @@ struct request_sock {
 	struct request_sock		*dl_next;
 	u16				mss;
 	u8				num_retrans; /* number of retransmits */
-	u8				cookie_ts:1; /* syncookie: encode tcpopts in timestamp */
+	u8				syncookie:1; /* syncookie: encode tcpopts in timestamp */
 	u8				num_timeout:7; /* number of timeouts */
 	u32				ts_recent;
 	struct timer_list		rsk_timer;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a018bafd7bdf..11a6f128e51c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6519,7 +6519,6 @@ static void tcp_openreq_init(struct request_sock *req,
 	struct inet_request_sock *ireq = inet_rsk(req);
 
 	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
-	req->cookie_ts = 0;
 	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
 	tcp_rsk(req)->snt_synack = 0;
@@ -6674,6 +6673,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	if (!req)
 		goto drop;
 
+	req->syncookie = want_cookie;
 	tcp_rsk(req)->af_specific = af_ops;
 	tcp_rsk(req)->ts_off = 0;
 #if IS_ENABLED(CONFIG_MPTCP)
@@ -6739,7 +6739,6 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 
 	if (want_cookie) {
 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
-		req->cookie_ts = tmp_opt.tstamp_ok;
 		if (!tmp_opt.tstamp_ok)
 			inet_rsk(req)->ecn_ok = 0;
 	}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index d8f16f6a9b02..85ff417bda7f 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3393,7 +3393,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 	memset(&opts, 0, sizeof(opts));
 	now = tcp_clock_ns();
 #ifdef CONFIG_SYN_COOKIES
-	if (unlikely(req->cookie_ts))
+	if (unlikely(synack_type == TCP_SYNACK_COOKIE && ireq->tstamp_ok))
 		skb->skb_mstamp_ns = cookie_init_timestamp(req, now);
 	else
 #endif
-- 
2.26.2

[PATCH v2 net-next 2/9] mptcp: token: move retry to caller

[Florian Westphal]

Once syncookie support is added, no state will be stored anymore when the
syn/ack is generated in syncookie mode.

When the ACK comes back, the generated key will be taken from the TCP ACK,
the token is re-generated and inserted into the token tree.

This means we can't retry with a new key when the token is already taken
in the syncookie case.

Therefore, move the retry logic to the caller to prepare for syncookie
support in mptcp.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/mptcp/subflow.c |  9 ++++++++-
 net/mptcp/token.c   | 12 ++++--------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 1c8482bc2ce5..9feb87880d1c 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -126,11 +126,18 @@ static void subflow_init_req(struct request_sock *req,
 	}
 
 	if (mp_opt.mp_capable && listener->request_mptcp) {
-		int err;
+		int err, retries = 4;
+
+again:
+		do {
+			get_random_bytes(&subflow_req->local_key, sizeof(subflow_req->local_key));
+		} while (subflow_req->local_key == 0);
 
 		err = mptcp_token_new_request(req);
 		if (err == 0)
 			subflow_req->mp_capable = 1;
+		else if (retries-- > 0)
+			goto again;
 
 		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
 	} else if (mp_opt.mp_join && listener->request_mptcp) {
diff --git a/net/mptcp/token.c b/net/mptcp/token.c
index 97cfc45bcc4f..f82410c54653 100644
--- a/net/mptcp/token.c
+++ b/net/mptcp/token.c
@@ -109,14 +109,12 @@ static void mptcp_crypto_key_gen_sha(u64 *key, u32 *token, u64 *idsn)
 int mptcp_token_new_request(struct request_sock *req)
 {
 	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
-	int retries = TOKEN_MAX_RETRIES;
 	struct token_bucket *bucket;
 	u32 token;
 
-again:
-	mptcp_crypto_key_gen_sha(&subflow_req->local_key,
-				 &subflow_req->token,
-				 &subflow_req->idsn);
+	mptcp_crypto_key_sha(subflow_req->local_key,
+			     &subflow_req->token,
+			     &subflow_req->idsn);
 	pr_debug("req=%p local_key=%llu, token=%u, idsn=%llu\n",
 		 req, subflow_req->local_key, subflow_req->token,
 		 subflow_req->idsn);
@@ -126,9 +124,7 @@ int mptcp_token_new_request(struct request_sock *req)
 	spin_lock_bh(&bucket->lock);
 	if (__token_bucket_busy(bucket, token)) {
 		spin_unlock_bh(&bucket->lock);
-		if (!--retries)
-			return -EBUSY;
-		goto again;
+		return -EBUSY;
 	}
 
 	hlist_nulls_add_head_rcu(&subflow_req->token_node, &bucket->req_chain);
-- 
2.26.2

Re: [PATCH v2 net-next 2/9] mptcp: token: move retry to caller

[Mat Martineau]

On Thu, 30 Jul 2020, Florian Westphal wrote:

> Once syncookie support is added, no state will be stored anymore when the
> syn/ack is generated in syncookie mode.
>
> When the ACK comes back, the generated key will be taken from the TCP ACK,
> the token is re-generated and inserted into the token tree.
>
> This means we can't retry with a new key when the token is already taken
> in the syncookie case.
>
> Therefore, move the retry logic to the caller to prepare for syncookie
> support in mptcp.
>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> net/mptcp/subflow.c |  9 ++++++++-
> net/mptcp/token.c   | 12 ++++--------
> 2 files changed, 12 insertions(+), 9 deletions(-)

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel

[PATCH v2 net-next 3/9] mptcp: subflow: split subflow_init_req

[Florian Westphal]

When syncookie support is added, we will need to add a variant of
subflow_init_req() helper.  It will do almost same thing except
that it will not compute/add a token to the mptcp token tree.

To avoid excess copy&paste, this commit splits away part of the
code into a new helper, __subflow_init_req, that can then be re-used
from the 'no insert' function added in a followup change.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/mptcp/subflow.c | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 9feb87880d1c..091e305a81c8 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -91,17 +91,9 @@ static struct mptcp_sock *subflow_token_join_request(struct request_sock *req,
 	return msk;
 }
 
-static void subflow_init_req(struct request_sock *req,
-			     const struct sock *sk_listener,
-			     struct sk_buff *skb)
+static int __subflow_init_req(struct request_sock *req, const struct sock *sk_listener)
 {
-	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);
 	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
-	struct mptcp_options_received mp_opt;
-
-	pr_debug("subflow_req=%p, listener=%p", subflow_req, listener);
-
-	mptcp_get_options(skb, &mp_opt);
 
 	subflow_req->mp_capable = 0;
 	subflow_req->mp_join = 0;
@@ -113,9 +105,29 @@ static void subflow_init_req(struct request_sock *req,
 	 * TCP option space.
 	 */
 	if (rcu_access_pointer(tcp_sk(sk_listener)->md5sig_info))
-		return;
+		return -EINVAL;
 #endif
 
+	return 0;
+}
+
+static void subflow_init_req(struct request_sock *req,
+			     const struct sock *sk_listener,
+			     struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct mptcp_options_received mp_opt;
+	int ret;
+
+	pr_debug("subflow_req=%p, listener=%p", subflow_req, listener);
+
+	ret = __subflow_init_req(req, sk_listener);
+	if (ret)
+		return;
+
+	mptcp_get_options(skb, &mp_opt);
+
 	if (mp_opt.mp_capable) {
 		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVE);
 
-- 
2.26.2

Re: [PATCH v2 net-next 3/9] mptcp: subflow: split subflow_init_req

[Mat Martineau]

On Thu, 30 Jul 2020, Florian Westphal wrote:

> When syncookie support is added, we will need to add a variant of
> subflow_init_req() helper.  It will do almost same thing except
> that it will not compute/add a token to the mptcp token tree.
>
> To avoid excess copy&paste, this commit splits away part of the
> code into a new helper, __subflow_init_req, that can then be re-used
> from the 'no insert' function added in a followup change.
>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> net/mptcp/subflow.c | 32 ++++++++++++++++++++++----------
> 1 file changed, 22 insertions(+), 10 deletions(-)
>

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel

[PATCH v2 net-next 4/9] mptcp: rename and export mptcp_subflow_request_sock_ops

[Florian Westphal]

syncookie code path needs to create an mptcp request sock.

Prepare for this and add mptcp prefix plus needed export of ops struct.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/net/mptcp.h |  1 +
 net/mptcp/subflow.c | 11 ++++++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 02158c257bd4..76eb915bf91c 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -58,6 +58,7 @@ struct mptcp_out_options {
 };
 
 #ifdef CONFIG_MPTCP
+extern struct request_sock_ops mptcp_subflow_request_sock_ops;
 
 void mptcp_init(void);
 
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 091e305a81c8..9b11d2b6ff4d 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -284,7 +284,8 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 	tcp_done(sk);
 }
 
-static struct request_sock_ops subflow_request_sock_ops;
+struct request_sock_ops mptcp_subflow_request_sock_ops;
+EXPORT_SYMBOL_GPL(mptcp_subflow_request_sock_ops);
 static struct tcp_request_sock_ops subflow_request_sock_ipv4_ops;
 
 static int subflow_v4_conn_request(struct sock *sk, struct sk_buff *skb)
@@ -297,7 +298,7 @@ static int subflow_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
 		goto drop;
 
-	return tcp_conn_request(&subflow_request_sock_ops,
+	return tcp_conn_request(&mptcp_subflow_request_sock_ops,
 				&subflow_request_sock_ipv4_ops,
 				sk, skb);
 drop:
@@ -322,7 +323,7 @@ static int subflow_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 	if (!ipv6_unicast_destination(skb))
 		goto drop;
 
-	return tcp_conn_request(&subflow_request_sock_ops,
+	return tcp_conn_request(&mptcp_subflow_request_sock_ops,
 				&subflow_request_sock_ipv6_ops, sk, skb);
 
 drop:
@@ -1311,8 +1312,8 @@ static int subflow_ops_init(struct request_sock_ops *subflow_ops)
 
 void __init mptcp_subflow_init(void)
 {
-	subflow_request_sock_ops = tcp_request_sock_ops;
-	if (subflow_ops_init(&subflow_request_sock_ops) != 0)
+	mptcp_subflow_request_sock_ops = tcp_request_sock_ops;
+	if (subflow_ops_init(&mptcp_subflow_request_sock_ops) != 0)
 		panic("MPTCP: failed to init subflow request sock ops\n");
 
 	subflow_request_sock_ipv4_ops = tcp_request_sock_ipv4_ops;
-- 
2.26.2

Re: [PATCH v2 net-next 4/9] mptcp: rename and export mptcp_subflow_request_sock_ops

[Mat Martineau]

On Thu, 30 Jul 2020, Florian Westphal wrote:

> syncookie code path needs to create an mptcp request sock.
>
> Prepare for this and add mptcp prefix plus needed export of ops struct.
>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> include/net/mptcp.h |  1 +
> net/mptcp/subflow.c | 11 ++++++-----
> 2 files changed, 7 insertions(+), 5 deletions(-)

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel

[PATCH v2 net-next 5/9] mptcp: subflow: add mptcp_subflow_init_cookie_req helper

[Florian Westphal]

Will be used to initialize the mptcp request socket when a MP_CAPABLE
request was handled in syncookie mode, i.e. when a TCP ACK containing a
MP_CAPABLE option is a valid syncookie value.

Normally (non-cookie case), MPTCP will generate a unique 32 bit connection
ID and stores it in the MPTCP token storage to be able to retrieve the
mptcp socket for subflow joining.

In syncookie case, we do not want to store any state, so just generate the
unique ID and use it in the reply.

This means there is a small window where another connection could generate
the same token.

When Cookie ACK comes back, we check that the token has not been registered
in the mean time.  If it was, the connection needs to fall back to TCP.

Changes in v2:
 - use req->syncookie instead of passing 'want_cookie' arg to ->init_req()
   (Eric Dumazet)

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/net/mptcp.h  | 10 +++++++++
 net/mptcp/protocol.h |  1 +
 net/mptcp/subflow.c  | 50 +++++++++++++++++++++++++++++++++++++++++++-
 net/mptcp/token.c    | 26 +++++++++++++++++++++++
 4 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 76eb915bf91c..3525d2822abe 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -131,6 +131,9 @@ static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
 }
 
 void mptcp_seq_show(struct seq_file *seq);
+int mptcp_subflow_init_cookie_req(struct request_sock *req,
+				  const struct sock *sk_listener,
+				  struct sk_buff *skb);
 #else
 
 static inline void mptcp_init(void)
@@ -200,6 +203,13 @@ static inline bool mptcp_skb_can_collapse(const struct sk_buff *to,
 
 static inline void mptcp_space(const struct sock *ssk, int *s, int *fs) { }
 static inline void mptcp_seq_show(struct seq_file *seq) { }
+
+static inline int mptcp_subflow_init_cookie_req(struct request_sock *req,
+						const struct sock *sk_listener,
+						struct sk_buff *skb)
+{
+	return 0; /* TCP fallback */
+}
 #endif /* CONFIG_MPTCP */
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index beb34b8a5363..d76d3b40d69e 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -400,6 +400,7 @@ void mptcp_token_destroy_request(struct request_sock *req);
 int mptcp_token_new_connect(struct sock *sk);
 void mptcp_token_accept(struct mptcp_subflow_request_sock *r,
 			struct mptcp_sock *msk);
+bool mptcp_token_exists(u32 token);
 struct mptcp_sock *mptcp_token_get_sock(u32 token);
 struct mptcp_sock *mptcp_token_iter_next(const struct net *net, long *s_slot,
 					 long *s_num);
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 9b11d2b6ff4d..3d346572d4c9 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -140,18 +140,31 @@ static void subflow_init_req(struct request_sock *req,
 	if (mp_opt.mp_capable && listener->request_mptcp) {
 		int err, retries = 4;
 
+		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
 again:
 		do {
 			get_random_bytes(&subflow_req->local_key, sizeof(subflow_req->local_key));
 		} while (subflow_req->local_key == 0);
 
+		if (unlikely(req->syncookie)) {
+			mptcp_crypto_key_sha(subflow_req->local_key,
+					     &subflow_req->token,
+					     &subflow_req->idsn);
+			if (mptcp_token_exists(subflow_req->token)) {
+				if (retries-- > 0)
+					goto again;
+			} else {
+				subflow_req->mp_capable = 1;
+			}
+			return;
+		}
+
 		err = mptcp_token_new_request(req);
 		if (err == 0)
 			subflow_req->mp_capable = 1;
 		else if (retries-- > 0)
 			goto again;
 
-		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
 	} else if (mp_opt.mp_join && listener->request_mptcp) {
 		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
 		subflow_req->mp_join = 1;
@@ -165,6 +178,41 @@ static void subflow_init_req(struct request_sock *req,
 	}
 }
 
+int mptcp_subflow_init_cookie_req(struct request_sock *req,
+				  const struct sock *sk_listener,
+				  struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct mptcp_options_received mp_opt;
+	int err;
+
+	err = __subflow_init_req(req, sk_listener);
+	if (err)
+		return err;
+
+	mptcp_get_options(skb, &mp_opt);
+
+	if (mp_opt.mp_capable && mp_opt.mp_join)
+		return -EINVAL;
+
+	if (mp_opt.mp_capable && listener->request_mptcp) {
+		if (mp_opt.sndr_key == 0)
+			return -EINVAL;
+
+		subflow_req->local_key = mp_opt.rcvr_key;
+		err = mptcp_token_new_request(req);
+		if (err)
+			return err;
+
+		subflow_req->mp_capable = 1;
+		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mptcp_subflow_init_cookie_req);
+
 static void subflow_v4_init_req(struct request_sock *req,
 				const struct sock *sk_listener,
 				struct sk_buff *skb)
diff --git a/net/mptcp/token.c b/net/mptcp/token.c
index f82410c54653..8b47c4bb1c6b 100644
--- a/net/mptcp/token.c
+++ b/net/mptcp/token.c
@@ -204,6 +204,32 @@ void mptcp_token_accept(struct mptcp_subflow_request_sock *req,
 	spin_unlock_bh(&bucket->lock);
 }
 
+bool mptcp_token_exists(u32 token)
+{
+	struct hlist_nulls_node *pos;
+	struct token_bucket *bucket;
+	struct mptcp_sock *msk;
+	struct sock *sk;
+
+	rcu_read_lock();
+	bucket = token_bucket(token);
+
+again:
+	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
+		msk = mptcp_sk(sk);
+		if (READ_ONCE(msk->token) == token)
+			goto found;
+	}
+	if (get_nulls_value(pos) != (token & token_mask))
+		goto again;
+
+	rcu_read_unlock();
+	return false;
+found:
+	rcu_read_unlock();
+	return true;
+}
+
 /**
  * mptcp_token_get_sock - retrieve mptcp connection sock using its token
  * @token: token of the mptcp connection to retrieve
-- 
2.26.2

Re: [PATCH v2 net-next 5/9] mptcp: subflow: add mptcp_subflow_init_cookie_req helper

[Mat Martineau]

On Thu, 30 Jul 2020, Florian Westphal wrote:

> Will be used to initialize the mptcp request socket when a MP_CAPABLE
> request was handled in syncookie mode, i.e. when a TCP ACK containing a
> MP_CAPABLE option is a valid syncookie value.
>
> Normally (non-cookie case), MPTCP will generate a unique 32 bit connection
> ID and stores it in the MPTCP token storage to be able to retrieve the
> mptcp socket for subflow joining.
>
> In syncookie case, we do not want to store any state, so just generate the
> unique ID and use it in the reply.
>
> This means there is a small window where another connection could generate
> the same token.
>
> When Cookie ACK comes back, we check that the token has not been registered
> in the mean time.  If it was, the connection needs to fall back to TCP.
>
> Changes in v2:
> - use req->syncookie instead of passing 'want_cookie' arg to ->init_req()
>   (Eric Dumazet)
>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> include/net/mptcp.h  | 10 +++++++++
> net/mptcp/protocol.h |  1 +
> net/mptcp/subflow.c  | 50 +++++++++++++++++++++++++++++++++++++++++++-
> net/mptcp/token.c    | 26 +++++++++++++++++++++++
> 4 files changed, 86 insertions(+), 1 deletion(-)

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel

[PATCH v2 net-next 6/9] tcp: syncookies: create mptcp request socket for ACK cookies with MPTCP option

[Florian Westphal]

If SYN packet contains MP_CAPABLE option, keep it enabled.
Syncokie validation and cookie-based socket creation is changed to
instantiate an mptcp request sockets if the ACK contains an MPTCP
connection request.

Rather than extend both cookie_v4/6_check, add a common helper to create
the (mp)tcp request socket.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/net/tcp.h     |  2 ++
 net/ipv4/syncookies.c | 38 ++++++++++++++++++++++++++++++++++----
 net/ipv4/tcp_input.c  |  3 ---
 net/ipv6/syncookies.c |  5 +----
 4 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index e0c35d56091f..dbf5c791a6eb 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -469,6 +469,8 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
 		      u32 cookie);
 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
+struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
+					    struct sock *sk, struct sk_buff *skb);
 #ifdef CONFIG_SYN_COOKIES
 
 /* Syncookies use a monotonic timer which increments every 60 seconds.
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 9a4f6b16c9bc..54838ee2e8d4 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -276,6 +276,39 @@ bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt,
 }
 EXPORT_SYMBOL(cookie_ecn_ok);
 
+struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
+					    struct sock *sk,
+					    struct sk_buff *skb)
+{
+	struct tcp_request_sock *treq;
+	struct request_sock *req;
+
+#ifdef CONFIG_MPTCP
+	if (sk_is_mptcp(sk))
+		ops = &mptcp_subflow_request_sock_ops;
+#endif
+
+	req = inet_reqsk_alloc(ops, sk, false);
+	if (!req)
+		return NULL;
+
+#if IS_ENABLED(CONFIG_MPTCP)
+	treq = tcp_rsk(req);
+	treq->is_mptcp = sk_is_mptcp(sk);
+	if (treq->is_mptcp) {
+		int err = mptcp_subflow_init_cookie_req(req, sk, skb);
+
+		if (err) {
+			reqsk_free(req);
+			return NULL;
+		}
+	}
+#endif
+
+	return req;
+}
+EXPORT_SYMBOL_GPL(cookie_tcp_reqsk_alloc);
+
 /* On input, sk is a listener.
  * Output is listener if incoming packet would not create a child
  *           NULL if memory could not be allocated.
@@ -326,7 +359,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 		goto out;
 
 	ret = NULL;
-	req = inet_reqsk_alloc(&tcp_request_sock_ops, sk, false); /* for safety */
+	req = cookie_tcp_reqsk_alloc(&tcp_request_sock_ops, sk, skb);
 	if (!req)
 		goto out;
 
@@ -350,9 +383,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	treq->snt_synack	= 0;
 	treq->tfo_listener	= false;
 
-	if (IS_ENABLED(CONFIG_MPTCP))
-		treq->is_mptcp = 0;
-
 	if (IS_ENABLED(CONFIG_SMC))
 		ireq->smc_ok = 0;
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 11a6f128e51c..739da25b0c23 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6701,9 +6701,6 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 
 	af_ops->init_req(req, sk, skb);
 
-	if (IS_ENABLED(CONFIG_MPTCP) && want_cookie)
-		tcp_rsk(req)->is_mptcp = 0;
-
 	if (security_inet_conn_request(sk, skb, req))
 		goto drop_and_free;
 
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 13235a012388..e796a64be308 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -170,7 +170,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		goto out;
 
 	ret = NULL;
-	req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false);
+	req = cookie_tcp_reqsk_alloc(&tcp6_request_sock_ops, sk, skb);
 	if (!req)
 		goto out;
 
@@ -178,9 +178,6 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	treq = tcp_rsk(req);
 	treq->tfo_listener = false;
 
-	if (IS_ENABLED(CONFIG_MPTCP))
-		treq->is_mptcp = 0;
-
 	if (security_inet_conn_request(sk, skb, req))
 		goto out_free;
 
-- 
2.26.2

[PATCH v2 net-next 7/9] mptcp: enable JOIN requests even if cookies are in use

[Florian Westphal]

JOIN requests do not work in syncookie mode -- for HMAC validation, the
peers nonce and the mptcp token (to obtain the desired connection socket
the join is for) are required, but this information is only present in the
initial syn.

So either we need to drop all JOIN requests once a listening socket enters
syncookie mode, or we need to store enough state to reconstruct the request
socket later.

This adds a state table (1024 entries) to store the data present in the
MP_JOIN syn request and the random nonce used for the cookie syn/ack.

When a MP_JOIN ACK passed cookie validation, the table is consulted
to rebuild the request socket from it.

An alternate approach would be to "cancel" syn-cookie mode and force
MP_JOIN to always use a syn queue entry.

However, doing so brings the backlog over the configured queue limit.

v2: use req->syncookie, not (removed) want_cookie arg

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/ipv4/syncookies.c  |   6 ++
 net/mptcp/Makefile     |   1 +
 net/mptcp/ctrl.c       |   1 +
 net/mptcp/protocol.h   |  20 +++++++
 net/mptcp/subflow.c    |  14 +++++
 net/mptcp/syncookies.c | 132 +++++++++++++++++++++++++++++++++++++++++
 6 files changed, 174 insertions(+)
 create mode 100644 net/mptcp/syncookies.c

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 54838ee2e8d4..11b20474be83 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -212,6 +212,12 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 		refcount_set(&req->rsk_refcnt, 1);
 		tcp_sk(child)->tsoffset = tsoff;
 		sock_rps_save_rxhash(child, skb);
+
+		if (tcp_rsk(req)->drop_req) {
+			refcount_set(&req->rsk_refcnt, 2);
+			return child;
+		}
+
 		if (inet_csk_reqsk_queue_add(sk, req, child))
 			return child;
 
diff --git a/net/mptcp/Makefile b/net/mptcp/Makefile
index 2360cbd27d59..a611968be4d7 100644
--- a/net/mptcp/Makefile
+++ b/net/mptcp/Makefile
@@ -4,6 +4,7 @@ obj-$(CONFIG_MPTCP) += mptcp.o
 mptcp-y := protocol.o subflow.o options.o token.o crypto.o ctrl.o pm.o diag.o \
 	   mib.o pm_netlink.o
 
+obj-$(CONFIG_SYN_COOKIES) += syncookies.o
 obj-$(CONFIG_INET_MPTCP_DIAG) += mptcp_diag.o
 
 mptcp_crypto_test-objs := crypto_test.o
diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 8e39585d37f3..54b888f94009 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -112,6 +112,7 @@ static struct pernet_operations mptcp_pernet_ops = {
 
 void __init mptcp_init(void)
 {
+	mptcp_join_cookie_init();
 	mptcp_proto_init();
 
 	if (register_pernet_subsys(&mptcp_pernet_ops) < 0)
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index d76d3b40d69e..60b27d44c184 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -506,4 +506,24 @@ static inline bool subflow_simultaneous_connect(struct sock *sk)
 	       !subflow->conn_finished;
 }
 
+#ifdef CONFIG_SYN_COOKIES
+void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,
+				       struct sk_buff *skb);
+bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,
+					struct sk_buff *skb);
+void __init mptcp_join_cookie_init(void);
+#else
+static inline void
+subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,
+				  struct sk_buff *skb) {}
+static inline bool
+mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,
+				   struct sk_buff *skb)
+{
+	return false;
+}
+
+static inline void mptcp_join_cookie_init(void) {}
+#endif
+
 #endif /* __MPTCP_PROTOCOL_H */
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 3d346572d4c9..a4cc4591bd4e 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -173,6 +173,12 @@ static void subflow_init_req(struct request_sock *req,
 		subflow_req->token = mp_opt.token;
 		subflow_req->remote_nonce = mp_opt.nonce;
 		subflow_req->msk = subflow_token_join_request(req, skb);
+
+		if (unlikely(req->syncookie) && subflow_req->msk) {
+			if (mptcp_can_accept_new_subflow(subflow_req->msk))
+				subflow_init_req_cookie_join_save(subflow_req, skb);
+		}
+
 		pr_debug("token=%u, remote_nonce=%u msk=%p", subflow_req->token,
 			 subflow_req->remote_nonce, subflow_req->msk);
 	}
@@ -207,6 +213,14 @@ int mptcp_subflow_init_cookie_req(struct request_sock *req,
 
 		subflow_req->mp_capable = 1;
 		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
+	} else if (mp_opt.mp_join && listener->request_mptcp) {
+		if (!mptcp_token_join_cookie_init_state(subflow_req, skb))
+			return -EINVAL;
+
+		if (mptcp_can_accept_new_subflow(subflow_req->msk))
+			subflow_req->mp_join = 1;
+
+		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
 	}
 
 	return 0;
diff --git a/net/mptcp/syncookies.c b/net/mptcp/syncookies.c
new file mode 100644
index 000000000000..6eb992789b50
--- /dev/null
+++ b/net/mptcp/syncookies.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/skbuff.h>
+
+#include "protocol.h"
+
+/* Syncookies do not work for JOIN requests.
+ *
+ * Unlike MP_CAPABLE, where the ACK cookie contains the needed MPTCP
+ * options to reconstruct the initial syn state, MP_JOIN does not contain
+ * the token to obtain the mptcp socket nor the server-generated nonce
+ * that was used in the cookie SYN/ACK response.
+ *
+ * Keep a small best effort state table to store the syn/synack data,
+ * indexed by skb hash.
+ *
+ * A MP_JOIN SYN packet handled by syn cookies is only stored if the 32bit
+ * token matches a known mptcp connection that can still accept more subflows.
+ *
+ * There is no timeout handling -- state is only re-constructed
+ * when the TCP ACK passed the cookie validation check.
+ */
+
+struct join_entry {
+	u32 token;
+	u32 remote_nonce;
+	u32 local_nonce;
+	u8 join_id;
+	u8 local_id;
+	u8 backup;
+	u8 valid;
+};
+
+#define COOKIE_JOIN_SLOTS	1024
+
+static struct join_entry join_entries[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;
+static spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;
+
+static u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net)
+{
+	u32 i = skb_get_hash(skb) ^ net_hash_mix(net);
+
+	return i % ARRAY_SIZE(join_entries);
+}
+
+static void mptcp_join_store_state(struct join_entry *entry,
+				   const struct mptcp_subflow_request_sock *subflow_req)
+{
+	entry->token = subflow_req->token;
+	entry->remote_nonce = subflow_req->remote_nonce;
+	entry->local_nonce = subflow_req->local_nonce;
+	entry->backup = subflow_req->backup;
+	entry->join_id = subflow_req->remote_id;
+	entry->local_id = subflow_req->local_id;
+	entry->valid = 1;
+}
+
+void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,
+				       struct sk_buff *skb)
+{
+	struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
+	u32 i = mptcp_join_entry_hash(skb, net);
+
+	/* No use in waiting if other cpu is already using this slot --
+	 * would overwrite the data that got stored.
+	 */
+	spin_lock_bh(&join_entry_locks[i]);
+	mptcp_join_store_state(&join_entries[i], subflow_req);
+	spin_unlock_bh(&join_entry_locks[i]);
+}
+
+/* Called for a cookie-ack with MP_JOIN option present.
+ * Look up the saved state based on skb hash & check token matches msk
+ * in same netns.
+ *
+ * Caller will check msk can still accept another subflow.  The hmac
+ * present in the cookie ACK mptcp option space will be checked later.
+ */
+bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,
+					struct sk_buff *skb)
+{
+	struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
+	u32 i = mptcp_join_entry_hash(skb, net);
+	struct mptcp_sock *msk;
+	struct join_entry *e;
+
+	e = &join_entries[i];
+
+	spin_lock_bh(&join_entry_locks[i]);
+
+	if (e->valid == 0) {
+		spin_unlock_bh(&join_entry_locks[i]);
+		return false;
+	}
+
+	e->valid = 0;
+
+	msk = mptcp_token_get_sock(e->token);
+	if (!msk) {
+		spin_unlock_bh(&join_entry_locks[i]);
+		return false;
+	}
+
+	/* If this fails, the token got re-used in the mean time by another
+	 * mptcp socket in a different netns, i.e. entry is outdated.
+	 */
+	if (!net_eq(sock_net((struct sock *)msk), net))
+		goto err_put;
+
+	subflow_req->remote_nonce = e->remote_nonce;
+	subflow_req->local_nonce = e->local_nonce;
+	subflow_req->backup = e->backup;
+	subflow_req->remote_id = e->join_id;
+	subflow_req->token = e->token;
+	subflow_req->msk = msk;
+	spin_unlock_bh(&join_entry_locks[i]);
+	return true;
+
+err_put:
+	spin_unlock_bh(&join_entry_locks[i]);
+	sock_put((struct sock *)msk);
+	return false;
+}
+
+void __init mptcp_join_cookie_init(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(join_entry_locks); i++)
+		spin_lock_init(&join_entry_locks[i]);
+
+	BUILD_BUG_ON(ARRAY_SIZE(join_entry_locks) != ARRAY_SIZE(join_entries));
+}
-- 
2.26.2

Re: [PATCH v2 net-next 7/9] mptcp: enable JOIN requests even if cookies are in use

[Mat Martineau]

On Thu, 30 Jul 2020, Florian Westphal wrote:

> JOIN requests do not work in syncookie mode -- for HMAC validation, the
> peers nonce and the mptcp token (to obtain the desired connection socket
> the join is for) are required, but this information is only present in the
> initial syn.
>
> So either we need to drop all JOIN requests once a listening socket enters
> syncookie mode, or we need to store enough state to reconstruct the request
> socket later.
>
> This adds a state table (1024 entries) to store the data present in the
> MP_JOIN syn request and the random nonce used for the cookie syn/ack.
>
> When a MP_JOIN ACK passed cookie validation, the table is consulted
> to rebuild the request socket from it.
>
> An alternate approach would be to "cancel" syn-cookie mode and force
> MP_JOIN to always use a syn queue entry.
>
> However, doing so brings the backlog over the configured queue limit.
>
> v2: use req->syncookie, not (removed) want_cookie arg
>
> Suggested-by: Paolo Abeni <pabeni@redhat.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> net/ipv4/syncookies.c  |   6 ++
> net/mptcp/Makefile     |   1 +
> net/mptcp/ctrl.c       |   1 +
> net/mptcp/protocol.h   |  20 +++++++
> net/mptcp/subflow.c    |  14 +++++
> net/mptcp/syncookies.c | 132 +++++++++++++++++++++++++++++++++++++++++
> 6 files changed, 174 insertions(+)
> create mode 100644 net/mptcp/syncookies.c

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel

Re: [PATCH v2 net-next 7/9] mptcp: enable JOIN requests even if cookies are in use

[Eric Dumazet]

On Thu, Jul 30, 2020 at 12:26 PM Florian Westphal <fw@strlen.de> wrote:
>
> JOIN requests do not work in syncookie mode -- for HMAC validation, the
> peers nonce and the mptcp token (to obtain the desired connection socket
> the join is for) are required, but this information is only present in the
> initial syn.
>
> So either we need to drop all JOIN requests once a listening socket enters
> syncookie mode, or we need to store enough state to reconstruct the request
> socket later.
>
> This adds a state table (1024 entries) to store the data present in the
> MP_JOIN syn request and the random nonce used for the cookie syn/ack.
>
> When a MP_JOIN ACK passed cookie validation, the table is consulted
> to rebuild the request socket from it.
>
> An alternate approach would be to "cancel" syn-cookie mode and force
> MP_JOIN to always use a syn queue entry.
>
> However, doing so brings the backlog over the configured queue limit.
>
> v2: use req->syncookie, not (removed) want_cookie arg
>
> Suggested-by: Paolo Abeni <pabeni@redhat.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  net/ipv4/syncookies.c  |   6 ++
>  net/mptcp/Makefile     |   1 +
>  net/mptcp/ctrl.c       |   1 +
>  net/mptcp/protocol.h   |  20 +++++++
>  net/mptcp/subflow.c    |  14 +++++
>  net/mptcp/syncookies.c | 132 +++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 174 insertions(+)
>  create mode 100644 net/mptcp/syncookies.c
>
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 54838ee2e8d4..11b20474be83 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -212,6 +212,12 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
>                 refcount_set(&req->rsk_refcnt, 1);
>                 tcp_sk(child)->tsoffset = tsoff;
>                 sock_rps_save_rxhash(child, skb);
> +
> +               if (tcp_rsk(req)->drop_req) {
> +                       refcount_set(&req->rsk_refcnt, 2);
> +                       return child;
> +               }
> +


Hey, what happened to CONFIG_MPTCP=n ?

net/ipv4/syncookies.c: In function 'tcp_get_cookie_sock':
net/ipv4/syncookies.c:216:19: error: 'struct tcp_request_sock' has no
member named 'drop_req'
  216 |   if (tcp_rsk(req)->drop_req) {
      |                   ^~
net/ipv4/syncookies.c: In function 'cookie_tcp_reqsk_alloc':
net/ipv4/syncookies.c:289:27: warning: unused variable 'treq'
[-Wunused-variable]
  289 |  struct tcp_request_sock *treq;
      |                           ^~~~
make[3]: *** [scripts/Makefile.build:280: net/ipv4/syncookies.o] Error 1
make[3]: *** Waiting for unfinished jobs....

[PATCH v2 net-next 8/9] selftests: mptcp: make 2nd net namespace use tcp syn cookies unconditionally

[Florian Westphal]

check we can establish connections also when syn cookies are in use.

Check that
MPTcpExtMPCapableSYNRX and MPTcpExtMPCapableACKRX increase for each
MPTCP test.

Check TcpExtSyncookiesSent and TcpExtSyncookiesRecv increase in netns2.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 .../selftests/net/mptcp/mptcp_connect.sh      | 47 +++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.sh b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
index c0589e071f20..57d75b7f6220 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
@@ -196,6 +196,9 @@ ip -net "$ns4" link set ns4eth3 up
 ip -net "$ns4" route add default via 10.0.3.2
 ip -net "$ns4" route add default via dead:beef:3::2
 
+# use TCP syn cookies, even if no flooding was detected.
+ip netns exec "$ns2" sysctl -q net.ipv4.tcp_syncookies=2
+
 set_ethtool_flags() {
 	local ns="$1"
 	local dev="$2"
@@ -407,6 +410,11 @@ do_transfer()
 		sleep 1
 	fi
 
+	local stat_synrx_last_l=$(ip netns exec ${listener_ns} nstat -z -a MPTcpExtMPCapableSYNRX | while read a count c rest ;do  echo $count;done)
+	local stat_ackrx_last_l=$(ip netns exec ${listener_ns} nstat -z -a MPTcpExtMPCapableACKRX | while read a count c rest ;do  echo $count;done)
+	local stat_cookietx_last=$(ip netns exec ${listener_ns} nstat -z -a TcpExtSyncookiesSent | while read a count c rest ;do  echo $count;done)
+	local stat_cookierx_last=$(ip netns exec ${listener_ns} nstat -z -a TcpExtSyncookiesRecv | while read a count c rest ;do  echo $count;done)
+
 	ip netns exec ${listener_ns} ./mptcp_connect -t $timeout -l -p $port -s ${srv_proto} $extra_args $local_addr < "$sin" > "$sout" &
 	local spid=$!
 
@@ -450,6 +458,45 @@ do_transfer()
 	check_transfer $cin $sout "file received by server"
 	rets=$?
 
+	local stat_synrx_now_l=$(ip netns exec ${listener_ns} nstat -z -a MPTcpExtMPCapableSYNRX  | while read a count c rest ;do  echo $count;done)
+	local stat_ackrx_now_l=$(ip netns exec ${listener_ns} nstat -z -a MPTcpExtMPCapableACKRX  | while read a count c rest ;do  echo $count;done)
+
+	local stat_cookietx_now=$(ip netns exec ${listener_ns} nstat -z -a TcpExtSyncookiesSent | while read a count c rest ;do  echo $count;done)
+	local stat_cookierx_now=$(ip netns exec ${listener_ns} nstat -z -a TcpExtSyncookiesRecv | while read a count c rest ;do  echo $count;done)
+
+	expect_synrx=$((stat_synrx_last_l))
+	expect_ackrx=$((stat_ackrx_last_l))
+
+	cookies=$(ip netns exec ${listener_ns} sysctl net.ipv4.tcp_syncookies)
+	cookies=${cookies##*=}
+
+	if [ ${cl_proto} = "MPTCP" ] && [ ${srv_proto} = "MPTCP" ]; then
+		expect_synrx=$((stat_synrx_last_l+1))
+		expect_ackrx=$((stat_ackrx_last_l+1))
+	fi
+	if [ $cookies -eq 2 ];then
+		if [ $stat_cookietx_last -ge $stat_cookietx_now ] ;then
+			echo "${listener_ns} CookieSent: ${cl_proto} -> ${srv_proto}: did not advance"
+		fi
+		if [ $stat_cookierx_last -ge $stat_cookierx_now ] ;then
+			echo "${listener_ns} CookieRecv: ${cl_proto} -> ${srv_proto}: did not advance"
+		fi
+	else
+		if [ $stat_cookietx_last -ne $stat_cookietx_now ] ;then
+			echo "${listener_ns} CookieSent: ${cl_proto} -> ${srv_proto}: changed"
+		fi
+		if [ $stat_cookierx_last -ne $stat_cookierx_now ] ;then
+			echo "${listener_ns} CookieRecv: ${cl_proto} -> ${srv_proto}: changed"
+		fi
+	fi
+
+	if [ $expect_synrx -ne $stat_synrx_now_l ] ;then
+		echo "${listener_ns} SYNRX: ${cl_proto} -> ${srv_proto}: expect ${expect_synrx}, got ${stat_synrx_now_l}"
+	fi
+	if [ $expect_ackrx -ne $stat_ackrx_now_l ] ;then
+		echo "${listener_ns} ACKRX: ${cl_proto} -> ${srv_proto}: expect ${expect_synrx}, got ${stat_synrx_now_l}"
+	fi
+
 	if [ $retc -eq 0 ] && [ $rets -eq 0 ];then
 		echo "$duration [ OK ]"
 		cat "$capout"
-- 
2.26.2

Re: [PATCH v2 net-next 8/9] selftests: mptcp: make 2nd net namespace use tcp syn cookies unconditionally

[Mat Martineau]

On Thu, 30 Jul 2020, Florian Westphal wrote:

> check we can establish connections also when syn cookies are in use.
>
> Check that
> MPTcpExtMPCapableSYNRX and MPTcpExtMPCapableACKRX increase for each
> MPTCP test.
>
> Check TcpExtSyncookiesSent and TcpExtSyncookiesRecv increase in netns2.
>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> .../selftests/net/mptcp/mptcp_connect.sh      | 47 +++++++++++++++++++
> 1 file changed, 47 insertions(+)

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel

[PATCH v2 net-next 9/9] selftests: mptcp: add test cases for mptcp join tests with syn cookies

[Florian Westphal]

Also add test cases with MP_JOIN when tcp_syncookies sysctl is 2 (i.e.,
syncookies are always-on).

While at it, also print the test number and add the test number
to the pcap files that can be generated optionally.

This makes it easier to match the pcap to the test case.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 .../testing/selftests/net/mptcp/mptcp_join.sh | 66 ++++++++++++++++++-
 1 file changed, 64 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index dd42c2f692d0..f39c1129ce5f 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -72,6 +72,15 @@ reset()
 	init
 }
 
+reset_with_cookies()
+{
+	reset
+
+	for netns in "$ns1" "$ns2";do
+		ip netns exec $netns sysctl -q net.ipv4.tcp_syncookies=2
+	done
+}
+
 for arg in "$@"; do
 	if [ "$arg" = "-c" ]; then
 		capture=1
@@ -138,7 +147,7 @@ do_transfer()
 			capuser="-Z $SUDO_USER"
 		fi
 
-		capfile="mp_join-${listener_ns}.pcap"
+		capfile=$(printf "mp_join-%02u-%s.pcap" "$TEST_COUNT" "${listener_ns}")
 
 		echo "Capturing traffic for test $TEST_COUNT into $capfile"
 		ip netns exec ${listener_ns} tcpdump -i any -s 65535 -B 32768 $capuser -w $capfile > "$capout" 2>&1 &
@@ -227,7 +236,7 @@ chk_join_nr()
 	local count
 	local dump_stats
 
-	printf "%-36s %s" "$msg" "syn"
+	printf "%02u %-36s %s" "$TEST_COUNT" "$msg" "syn"
 	count=`ip netns exec $ns1 nstat -as | grep MPTcpExtMPJoinSynRx | awk '{print $2}'`
 	[ -z "$count" ] && count=0
 	if [ "$count" != "$syn_nr" ]; then
@@ -354,4 +363,57 @@ ip netns exec $ns2 ./pm_nl_ctl add 10.0.4.2 flags subflow
 run_tests $ns1 $ns2 10.0.1.1
 chk_join_nr "multiple subflows and signal" 3 3 3
 
+# single subflow, syncookies
+reset_with_cookies
+ip netns exec $ns1 ./pm_nl_ctl limits 0 1
+ip netns exec $ns2 ./pm_nl_ctl limits 0 1
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.3.2 flags subflow
+run_tests $ns1 $ns2 10.0.1.1
+chk_join_nr "single subflow with syn cookies" 1 1 1
+
+# multiple subflows with syn cookies
+reset_with_cookies
+ip netns exec $ns1 ./pm_nl_ctl limits 0 2
+ip netns exec $ns2 ./pm_nl_ctl limits 0 2
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.3.2 flags subflow
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.2.2 flags subflow
+run_tests $ns1 $ns2 10.0.1.1
+chk_join_nr "multiple subflows with syn cookies" 2 2 2
+
+# multiple subflows limited by server
+reset_with_cookies
+ip netns exec $ns1 ./pm_nl_ctl limits 0 1
+ip netns exec $ns2 ./pm_nl_ctl limits 0 2
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.3.2 flags subflow
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.2.2 flags subflow
+run_tests $ns1 $ns2 10.0.1.1
+chk_join_nr "subflows limited by server w cookies" 2 2 1
+
+# test signal address with cookies
+reset_with_cookies
+ip netns exec $ns1 ./pm_nl_ctl limits 0 1
+ip netns exec $ns2 ./pm_nl_ctl limits 1 1
+ip netns exec $ns1 ./pm_nl_ctl add 10.0.2.1 flags signal
+run_tests $ns1 $ns2 10.0.1.1
+chk_join_nr "signal address with syn cookies" 1 1 1
+
+# test cookie with subflow and signal
+reset_with_cookies
+ip netns exec $ns1 ./pm_nl_ctl add 10.0.2.1 flags signal
+ip netns exec $ns1 ./pm_nl_ctl limits 0 2
+ip netns exec $ns2 ./pm_nl_ctl limits 1 2
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.3.2 flags subflow
+run_tests $ns1 $ns2 10.0.1.1
+chk_join_nr "subflow and signal w cookies" 2 2 2
+
+# accept and use add_addr with additional subflows
+reset_with_cookies
+ip netns exec $ns1 ./pm_nl_ctl limits 0 3
+ip netns exec $ns1 ./pm_nl_ctl add 10.0.2.1 flags signal
+ip netns exec $ns2 ./pm_nl_ctl limits 1 3
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.3.2 flags subflow
+ip netns exec $ns2 ./pm_nl_ctl add 10.0.4.2 flags subflow
+run_tests $ns1 $ns2 10.0.1.1
+chk_join_nr "subflows and signal w. cookies" 3 3 3
+
 exit $ret
-- 
2.26.2

Re: [PATCH v2 net-next 9/9] selftests: mptcp: add test cases for mptcp join tests with syn cookies

[Mat Martineau]

On Thu, 30 Jul 2020, Florian Westphal wrote:

> Also add test cases with MP_JOIN when tcp_syncookies sysctl is 2 (i.e.,
> syncookies are always-on).
>
> While at it, also print the test number and add the test number
> to the pcap files that can be generated optionally.
>
> This makes it easier to match the pcap to the test case.
>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> .../testing/selftests/net/mptcp/mptcp_join.sh | 66 ++++++++++++++++++-
> 1 file changed, 64 insertions(+), 2 deletions(-)

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

--
Mat Martineau
Intel

Re: [PATCH v2 net-next 0/9] mptcp: add syncookie support

[David Miller]

From: Florian Westphal <fw@strlen.de>
Date: Thu, 30 Jul 2020 21:25:49 +0200

> Changes in v2:
 ...
> When syn-cookies are used the SYN?ACK never contains a MPTCP option,
> because the code path that creates a request socket based on a valid
> cookie ACK lacks the needed changes to construct MPTCP request sockets.
> 
> After this series, if SYN carries MP_CAPABLE option, the option is not
> cleared anymore and request socket will be reconstructed using the
> MP_CAPABLE option data that is re-sent with the ACK.
> 
> This means that no additional state gets encoded into the syn cookie or
> the TCP timestamp.
 ...

Series applied, thanks Florian.

Re: [PATCH v2 net-next 0/9] mptcp: add syncookie support

[Eric Dumazet]

On 7/31/20 4:56 PM, David Miller wrote:
> From: Florian Westphal <fw@strlen.de>
> Date: Thu, 30 Jul 2020 21:25:49 +0200
> 
>> Changes in v2:
>  ...
>> When syn-cookies are used the SYN?ACK never contains a MPTCP option,
>> because the code path that creates a request socket based on a valid
>> cookie ACK lacks the needed changes to construct MPTCP request sockets.
>>
>> After this series, if SYN carries MP_CAPABLE option, the option is not
>> cleared anymore and request socket will be reconstructed using the
>> MP_CAPABLE option data that is re-sent with the ACK.
>>
>> This means that no additional state gets encoded into the syn cookie or
>> the TCP timestamp.
>  ...
> 
> Series applied, thanks Florian.
> 

Build is broken

I had to use :

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 11b20474be8310d7070750a1c7b4013f2fba2f55..f0794f0232bae749244fff35d8b96b1f561a5e87 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -213,7 +213,7 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
                tcp_sk(child)->tsoffset = tsoff;
                sock_rps_save_rxhash(child, skb);
 
-               if (tcp_rsk(req)->drop_req) {
+               if (rsk_drop_req(req)) {
                        refcount_set(&req->rsk_refcnt, 2);
                        return child;
                }
@@ -286,10 +286,11 @@ struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
                                            struct sock *sk,
                                            struct sk_buff *skb)
 {
-       struct tcp_request_sock *treq;
        struct request_sock *req;
 
 #ifdef CONFIG_MPTCP
+       struct tcp_request_sock *treq;
+
        if (sk_is_mptcp(sk))
                ops = &mptcp_subflow_request_sock_ops;
 #endif