Merge: mptcp: phase-1 backports for RHEL-10.2

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/1560

JIRA: https://issues.redhat.com/browse/RHEL-115576
Upstream Status: all mainline in net.git
Conflicts: only one, see individual patches
Tested: boot-tested only
Omitted-fix: e84cb86 ("mptcp: pm: in-kernel: C-flag: handle late ADD_ADDR") :
  the new test on 'C' flag can be flaky, we can stabilize it later in the developement phase

Note: the upstream path manager has been re-worked so much that no present/future patch
in that area  would apply, unless all the re-work patches are backported. Therefore, the
following series:

- 71ca356 ("Merge branch 'mptcp-pm-code-reorganisation'")
- 8121227 ("Merge branch 'mptcp-pm-misc-cleanups-part-2'")
- 7842f3d ("Merge branch 'mptcp-pm-misc-cleanups-part-3'")

plus some sparse "zero-impact" commits reworking the MPTCP path manager have been included.

Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Approved-by: Florian Westphal <fwestpha@redhat.com>
Approved-by: Paolo Abeni <pabeni@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

Documentation/netlink/specs/mptcp_pm.yaml

@@ -22,65 +22,67 @@ definitions:
       doc: unused event
      -
       name: created
-      doc:
-        token, family, saddr4 | saddr6, daddr4 | daddr6, sport, dport
+      doc: >-
         A new MPTCP connection has been created. It is the good time to
         allocate memory and send ADD_ADDR if needed. Depending on the
         traffic-patterns it can take a long time until the
         MPTCP_EVENT_ESTABLISHED is sent.
+        Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6, sport,
+        dport, server-side, [flags].
      -
       name: established
-      doc:
-        token, family, saddr4 | saddr6, daddr4 | daddr6, sport, dport
+      doc: >-
         A MPTCP connection is established (can start new subflows).
+        Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6, sport,
+        dport, server-side, [flags].
      -
       name: closed
-      doc:
-        token
+      doc: >-
         A MPTCP connection has stopped.
+        Attribute: token.
      -
       name: announced
       value: 6
-      doc:
-        token, rem_id, family, daddr4 | daddr6 [, dport]
+      doc: >-
         A new address has been announced by the peer.
+        Attributes: token, rem_id, family, daddr4 | daddr6 [, dport].
      -
       name: removed
-      doc:
-        token, rem_id
+      doc: >-
         An address has been lost by the peer.
+        Attributes: token, rem_id.
      -
       name: sub-established
       value: 10
-      doc:
-        token, family, loc_id, rem_id, saddr4 | saddr6, daddr4 | daddr6, sport,
-        dport, backup, if_idx [, error]
+      doc: >-
         A new subflow has been established. 'error' should not be set.
+        Attributes: token, family, loc_id, rem_id, saddr4 | saddr6, daddr4 |
+        daddr6, sport, dport, backup, if_idx [, error].
      -
       name: sub-closed
-      doc:
-        token, family, loc_id, rem_id, saddr4 | saddr6, daddr4 | daddr6, sport,
-        dport, backup, if_idx [, error]
+      doc: >-
         A subflow has been closed. An error (copy of sk_err) could be set if an
         error has been detected for this subflow.
+        Attributes: token, family, loc_id, rem_id, saddr4 | saddr6, daddr4 |
+        daddr6, sport, dport, backup, if_idx [, error].
      -
       name: sub-priority
       value: 13
-      doc:
-        token, family, loc_id, rem_id, saddr4 | saddr6, daddr4 | daddr6, sport,
-        dport, backup, if_idx [, error]
+      doc: >-
         The priority of a subflow has changed. 'error' should not be set.
+        Attributes: token, family, loc_id, rem_id, saddr4 | saddr6, daddr4 |
+        daddr6, sport, dport, backup, if_idx [, error].
      -
       name: listener-created
       value: 15
-      doc:
-        family, sport, saddr4 | saddr6
+      doc: >-
         A new PM listener is created.
+        Attributes: family, sport, saddr4 | saddr6.
      -
       name: listener-closed
-      doc:
-        family, sport, saddr4 | saddr6
+      doc: >-
         A PM listener is closed.
+        Attributes: family, sport, saddr4 | saddr6.
 
 attribute-sets:
   -

Documentation/networking/mptcp-sysctl.rst

@@ -12,6 +12,8 @@ add_addr_timeout - INTEGER (seconds)
 	resent to an MPTCP peer that has not acknowledged a previous
 	ADD_ADDR message.
 
+	Do not retransmit if set to 0.
+
 	The default value matches TCP_RTO_MAX. This is a per-namespace
 	sysctl.
 
@@ -108,3 +110,19 @@ stale_loss_cnt - INTEGER
 	This is a per-namespace sysctl.
 
 	Default: 4
+
+syn_retrans_before_tcp_fallback - INTEGER
+	The number of SYN + MP_CAPABLE retransmissions before falling back to
+	TCP, i.e. dropping the MPTCP options. In other words, if all the packets
+	are dropped on the way, there will be:
+
+	* The initial SYN with MPTCP support
+	* This number of SYN retransmitted with MPTCP support
+	* The next SYN retransmissions will be without MPTCP support
+
+	0 means the first retransmission will be done without MPTCP options.
+	>= 128 means that all SYN retransmissions will keep the MPTCP options. A
+	lower number might increase false-positive MPTCP blackholes detections.
+	This is a per-namespace sysctl.
+
+	Default: 2

include/net/mptcp.h

@@ -100,17 +100,9 @@ struct mptcp_out_options {
 #define MPTCP_SCHED_MAX		128
 #define MPTCP_SCHED_BUF_MAX	(MPTCP_SCHED_NAME_MAX * MPTCP_SCHED_MAX)
 
-#define MPTCP_SUBFLOWS_MAX	8
-
-struct mptcp_sched_data {
-	bool	reinject;
-	u8	subflows;
-	struct mptcp_subflow_context *contexts[MPTCP_SUBFLOWS_MAX];
-};
-
 struct mptcp_sched_ops {
-	int (*get_subflow)(struct mptcp_sock *msk,
-			   struct mptcp_sched_data *data);
+	int (*get_send)(struct mptcp_sock *msk);
+	int (*get_retrans)(struct mptcp_sock *msk);
 
 	char			name[MPTCP_SCHED_NAME_MAX];
 	struct module		*owner;

include/uapi/linux/mptcp.h

@@ -31,6 +31,8 @@
 #define MPTCP_INFO_FLAG_FALLBACK		_BITUL(0)
 #define MPTCP_INFO_FLAG_REMOTE_KEY_RECEIVED	_BITUL(1)
 
+#define MPTCP_PM_EV_FLAG_DENY_JOIN_ID0		_BITUL(0)
+
 #define MPTCP_PM_ADDR_FLAG_SIGNAL                      (1 << 0)
 #define MPTCP_PM_ADDR_FLAG_SUBFLOW                     (1 << 1)
 #define MPTCP_PM_ADDR_FLAG_BACKUP                      (1 << 2)

include/uapi/linux/mptcp_pm.h

@@ -12,31 +12,33 @@
 /**
  * enum mptcp_event_type
  * @MPTCP_EVENT_UNSPEC: unused event
- * @MPTCP_EVENT_CREATED: token, family, saddr4 | saddr6, daddr4 | daddr6,
- *   sport, dport A new MPTCP connection has been created. It is the good time
- *   to allocate memory and send ADD_ADDR if needed. Depending on the
+ * @MPTCP_EVENT_CREATED: A new MPTCP connection has been created. It is the
+ *   good time to allocate memory and send ADD_ADDR if needed. Depending on the
  *   traffic-patterns it can take a long time until the MPTCP_EVENT_ESTABLISHED
- *   is sent.
- * @MPTCP_EVENT_ESTABLISHED: token, family, saddr4 | saddr6, daddr4 | daddr6,
- *   sport, dport A MPTCP connection is established (can start new subflows).
- * @MPTCP_EVENT_CLOSED: token A MPTCP connection has stopped.
- * @MPTCP_EVENT_ANNOUNCED: token, rem_id, family, daddr4 | daddr6 [, dport] A
- *   new address has been announced by the peer.
- * @MPTCP_EVENT_REMOVED: token, rem_id An address has been lost by the peer.
- * @MPTCP_EVENT_SUB_ESTABLISHED: token, family, loc_id, rem_id, saddr4 |
- *   saddr6, daddr4 | daddr6, sport, dport, backup, if_idx [, error] A new
- *   subflow has been established. 'error' should not be set.
- * @MPTCP_EVENT_SUB_CLOSED: token, family, loc_id, rem_id, saddr4 | saddr6,
- *   daddr4 | daddr6, sport, dport, backup, if_idx [, error] A subflow has been
- *   closed. An error (copy of sk_err) could be set if an error has been
- *   detected for this subflow.
- * @MPTCP_EVENT_SUB_PRIORITY: token, family, loc_id, rem_id, saddr4 | saddr6,
- *   daddr4 | daddr6, sport, dport, backup, if_idx [, error] The priority of a
- *   subflow has changed. 'error' should not be set.
- * @MPTCP_EVENT_LISTENER_CREATED: family, sport, saddr4 | saddr6 A new PM
- *   listener is created.
- * @MPTCP_EVENT_LISTENER_CLOSED: family, sport, saddr4 | saddr6 A PM listener
- *   is closed.
+ *   is sent. Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6,
+ *   sport, dport, server-side, [flags].
+ * @MPTCP_EVENT_ESTABLISHED: A MPTCP connection is established (can start new
+ *   subflows). Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6,
+ *   sport, dport, server-side, [flags].
+ * @MPTCP_EVENT_CLOSED: A MPTCP connection has stopped. Attribute: token.
+ * @MPTCP_EVENT_ANNOUNCED: A new address has been announced by the peer.
+ *   Attributes: token, rem_id, family, daddr4 | daddr6 [, dport].
+ * @MPTCP_EVENT_REMOVED: An address has been lost by the peer. Attributes:
+ *   token, rem_id.
+ * @MPTCP_EVENT_SUB_ESTABLISHED: A new subflow has been established. 'error'
+ *   should not be set. Attributes: token, family, loc_id, rem_id, saddr4 |
+ *   saddr6, daddr4 | daddr6, sport, dport, backup, if_idx [, error].
+ * @MPTCP_EVENT_SUB_CLOSED: A subflow has been closed. An error (copy of
+ *   sk_err) could be set if an error has been detected for this subflow.
+ *   Attributes: token, family, loc_id, rem_id, saddr4 | saddr6, daddr4 |
+ *   daddr6, sport, dport, backup, if_idx [, error].
+ * @MPTCP_EVENT_SUB_PRIORITY: The priority of a subflow has changed. 'error'
+ *   should not be set. Attributes: token, family, loc_id, rem_id, saddr4 |
+ *   saddr6, daddr4 | daddr6, sport, dport, backup, if_idx [, error].
+ * @MPTCP_EVENT_LISTENER_CREATED: A new PM listener is created. Attributes:
+ *   family, sport, saddr4 | saddr6.
+ * @MPTCP_EVENT_LISTENER_CLOSED: A PM listener is closed. Attributes: family,
+ *   sport, saddr4 | saddr6.
  */
 enum mptcp_event_type {
 	MPTCP_EVENT_UNSPEC,

net/mptcp/Makefile

@@ -3,7 +3,7 @@ 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 sockopt.o pm_userspace.o fastopen.o sched.o \
-	   mptcp_pm_gen.o
+	   mptcp_pm_gen.o pm_kernel.o
 
 obj-$(CONFIG_SYN_COOKIES) += syncookies.o
 obj-$(CONFIG_INET_MPTCP_DIAG) += mptcp_diag.o

net/mptcp/ctrl.c

@@ -32,6 +32,7 @@ struct mptcp_pernet {
 	unsigned int close_timeout;
 	unsigned int stale_loss_cnt;
 	atomic_t active_disable_times;
+	u8 syn_retrans_before_tcp_fallback;
 	unsigned long active_disable_stamp;
 	u8 mptcp_enabled;
 	u8 checksum_enabled;
@@ -92,6 +93,7 @@ static void mptcp_pernet_set_defaults(struct mptcp_pernet *pernet)
 	pernet->mptcp_enabled = 0;
 	pernet->add_addr_timeout = TCP_RTO_MAX;
 	pernet->blackhole_timeout = 3600;
+	pernet->syn_retrans_before_tcp_fallback = 2;
 	atomic_set(&pernet->active_disable_times, 0);
 	pernet->close_timeout = TCP_TIMEWAIT_LEN;
 	pernet->checksum_enabled = 0;
@@ -245,6 +247,12 @@ static struct ctl_table mptcp_sysctl_table[] = {
 		.proc_handler = proc_blackhole_detect_timeout,
 		.extra1 = SYSCTL_ZERO,
 	},
+	{
+		.procname = "syn_retrans_before_tcp_fallback",
+		.maxlen = sizeof(u8),
+		.mode = 0644,
+		.proc_handler = proc_dou8vec_minmax,
+	},
 };
 
 static int mptcp_pernet_new_table(struct net *net, struct mptcp_pernet *pernet)
@@ -269,6 +277,7 @@ static int mptcp_pernet_new_table(struct net *net, struct mptcp_pernet *pernet)
 	/* table[7] is for available_schedulers which is read-only info */
 	table[8].data = &pernet->close_timeout;
 	table[9].data = &pernet->blackhole_timeout;
+	table[10].data = &pernet->syn_retrans_before_tcp_fallback;
 
 	hdr = register_net_sysctl_sz(net, MPTCP_SYSCTL_PATH, table,
 				     ARRAY_SIZE(mptcp_sysctl_table));
@@ -385,29 +394,39 @@ void mptcp_active_enable(struct sock *sk)
 
 		if (dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK))
 			atomic_set(&pernet->active_disable_times, 0);
+
+		dst_release(dst);
 	}
 }
 
 /* Check the number of retransmissions, and fallback to TCP if needed */
 void mptcp_active_detect_blackhole(struct sock *ssk, bool expired)
 {
 	struct mptcp_subflow_context *subflow;
-	u32 timeouts;
+	u8 timeouts, to_max;
+	struct net *net;
 
-	if (!sk_is_mptcp(ssk))
+	/* Only check MPTCP SYN ... */
+	if (likely(!sk_is_mptcp(ssk) || ssk->sk_state != TCP_SYN_SENT))
 		return;
 
-	timeouts = inet_csk(ssk)->icsk_retransmits;
 	subflow = mptcp_subflow_ctx(ssk);
 
-	if (subflow->request_mptcp && ssk->sk_state == TCP_SYN_SENT) {
-		if (timeouts == 2 || (timeouts < 2 && expired)) {
-			MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPCAPABLEACTIVEDROP);
-			subflow->mpc_drop = 1;
-			mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow);
-		}
-	} else if (ssk->sk_state == TCP_SYN_SENT) {
+	/* ... + MP_CAPABLE */
+	if (!subflow->request_mptcp) {
+		/* Mark as blackhole iif the 1st non-MPTCP SYN is accepted */
 		subflow->mpc_drop = 0;
+		return;
+	}
+
+	net = sock_net(ssk);
+	timeouts = inet_csk(ssk)->icsk_retransmits;
+	to_max = mptcp_get_pernet(net)->syn_retrans_before_tcp_fallback;
+
+	if (timeouts == to_max || (timeouts < to_max && expired)) {
+		MPTCP_INC_STATS(net, MPTCP_MIB_MPCAPABLEACTIVEDROP);
+		subflow->mpc_drop = 1;
+		mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow);
 	}
 }
 

net/mptcp/diag.c

@@ -47,7 +47,7 @@ static int subflow_get_info(struct sock *sk, struct sk_buff *skb, bool net_admin
 		flags |= MPTCP_SUBFLOW_FLAG_BKUP_REM;
 	if (sf->request_bkup)
 		flags |= MPTCP_SUBFLOW_FLAG_BKUP_LOC;
-	if (sf->fully_established)
+	if (READ_ONCE(sf->fully_established))
 		flags |= MPTCP_SUBFLOW_FLAG_FULLY_ESTABLISHED;
 	if (sf->conn_finished)
 		flags |= MPTCP_SUBFLOW_FLAG_CONNECTED;

net/mptcp/options.c

@@ -458,7 +458,7 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 		return false;
 
 	/* MPC/MPJ needed only on 3rd ack packet, DATA_FIN and TCP shutdown take precedence */
-	if (subflow->fully_established || snd_data_fin_enable ||
+	if (READ_ONCE(subflow->fully_established) || snd_data_fin_enable ||
 	    subflow->snd_isn != TCP_SKB_CB(skb)->seq ||
 	    sk->sk_state != TCP_ESTABLISHED)
 		return false;
@@ -935,7 +935,7 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
 	/* here we can process OoO, in-window pkts, only in-sequence 4th ack
 	 * will make the subflow fully established
 	 */
-	if (likely(subflow->fully_established)) {
+	if (likely(READ_ONCE(subflow->fully_established))) {
 		/* on passive sockets, check for 3rd ack retransmission
 		 * note that msk is always set by subflow_syn_recv_sock()
 		 * for mp_join subflows
@@ -979,18 +979,19 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
 		if (subflow->mp_join)
 			goto reset;
 		subflow->mp_capable = 0;
+		if (!mptcp_try_fallback(ssk))
+			goto reset;
 		pr_fallback(msk);
-		mptcp_do_fallback(ssk);
 		return false;
 	}
 
-	if (mp_opt->deny_join_id0)
-		WRITE_ONCE(msk->pm.remote_deny_join_id0, true);
-
 	if (unlikely(!READ_ONCE(msk->pm.server_side)))
 		pr_warn_once("bogus mpc option on established client sk");
 
 set_fully_established:
+	if (mp_opt->deny_join_id0)
+		WRITE_ONCE(msk->pm.remote_deny_join_id0, true);
+
 	mptcp_data_lock((struct sock *)msk);
 	__mptcp_subflow_fully_established(msk, subflow, mp_opt);
 	mptcp_data_unlock((struct sock *)msk);
@@ -1117,7 +1118,9 @@ static bool add_addr_hmac_valid(struct mptcp_sock *msk,
 	return hmac == mp_opt->ahmac;
 }
 
-/* Return false if a subflow has been reset, else return true */
+/* Return false in case of error (or subflow has been reset),
+ * else return true.
+ */
 bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
@@ -1221,7 +1224,7 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 
 	mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
 	if (!mpext)
-		return true;
+		return false;
 
 	memset(mpext, 0, sizeof(*mpext));