bfdd: implement minimum TTL

Initial BFD protocol implementation had a hard coded value of maximum 5
hops, now we have a configurable hop amount with a safe default of 1
hop.

Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>

10 files changed, 200 insertions, 6 deletions

diff --git a/bfdd/bfd.c b/bfdd/bfd.c
index 1fc922475..2b3caa6fe 100644
--- a/bfdd/bfd.c
+++ b/bfdd/bfd.c
@@ -89,6 +89,7 @@ static void bfd_profile_set_default(struct bfd_profile *bp)
 	bp->detection_multiplier = BFD_DEFDETECTMULT;
 	bp->echo_mode = false;
 	bp->passive = false;
+	bp->minimum_ttl = BFD_DEF_MHOP_TTL;
 	bp->min_echo_rx = BFD_DEF_REQ_MIN_ECHO;
 	bp->min_rx = BFD_DEFREQUIREDMINRX;
 	bp->min_tx = BFD_DEFDESIREDMINTX;
@@ -190,6 +191,12 @@ void bfd_session_apply(struct bfd_session *bs)
 			bfd_set_echo(bs, bp->echo_mode);
 		else
 			bfd_set_echo(bs, bs->peer_profile.echo_mode);
+	} else {
+		/* Configure the TTL packet filter. */
+		if (bs->peer_profile.minimum_ttl == BFD_DEF_MHOP_TTL)
+			bs->mh_ttl = bp->minimum_ttl;
+		else
+			bs->mh_ttl = bs->peer_profile.minimum_ttl;
 	}
 
 	/* Toggle 'passive-mode' if default value. */
@@ -752,6 +759,11 @@ static void _bfd_session_update(struct bfd_session *bs,
 	else
 		UNSET_FLAG(bs->flags, BFD_SESS_FLAG_CBIT);
 
+	if (bpc->bpc_has_minimum_ttl) {
+		bs->mh_ttl = bpc->bpc_minimum_ttl;
+		bs->peer_profile.minimum_ttl = bpc->bpc_minimum_ttl;
+	}
+
 	bs->peer_profile.echo_mode = bpc->bpc_echo;
 	bfd_set_echo(bs, bpc->bpc_echo);
 
diff --git a/bfdd/bfd.h b/bfdd/bfd.h
index 4f88e6b2e..af3f92d6a 100644
--- a/bfdd/bfd.h
+++ b/bfdd/bfd.h
@@ -210,6 +210,8 @@ struct bfd_profile {
 	bool admin_shutdown;
 	/** Passive mode. */
 	bool passive;
+	/** Minimum expected TTL value. */
+	uint8_t minimum_ttl;
 
 	/** Echo mode (only applies to single hop). */
 	bool echo_mode;
@@ -331,7 +333,8 @@ TAILQ_HEAD(obslist, bfd_session_observer);
 #define BFD_DEFREQUIREDMINRX (300 * 1000) /* microseconds. */
 #define BFD_DEF_REQ_MIN_ECHO (50 * 1000) /* microseconds. */
 #define BFD_DEF_SLOWTX (1000 * 1000) /* microseconds. */
-#define BFD_DEF_MHOP_TTL 5
+/** Minimum multi hop TTL. */
+#define BFD_DEF_MHOP_TTL 254
 #define BFD_PKT_LEN 24 /* Length of control packet */
 #define BFD_TTL_VAL 255
 #define BFD_RCV_TTL_VAL 1
diff --git a/bfdd/bfd_packet.c b/bfdd/bfd_packet.c
index 68bdd89bb..38855acff 100644
--- a/bfdd/bfd_packet.c
+++ b/bfdd/bfd_packet.c
@@ -577,7 +577,7 @@ int bfd_recv_cb(struct thread *t)
 		return 0;
 	}
 
-	/* Validate packet TTL. */
+	/* Validate single hop packet TTL. */
 	if ((!is_mhop) && (ttl != BFD_TTL_VAL)) {
 		cp_debug(is_mhop, &peer, &local, ifindex, vrfid,
 			 "invalid TTL: %d expected %d", ttl, BFD_TTL_VAL);
@@ -630,10 +630,10 @@ int bfd_recv_cb(struct thread *t)
 	 * Single hop: set local address that received the packet.
 	 */
 	if (is_mhop) {
-		if ((BFD_TTL_VAL - bfd->mh_ttl) > BFD_TTL_VAL) {
+		if (ttl < bfd->mh_ttl) {
 			cp_debug(is_mhop, &peer, &local, ifindex, vrfid,
 				 "exceeded max hop count (expected %d, got %d)",
-				 bfd->mh_ttl, BFD_TTL_VAL);
+				 bfd->mh_ttl, ttl);
 			return 0;
 		}
 	} else if (bfd->local_address.sa_sin.sin_family == AF_UNSPEC) {
diff --git a/bfdd/bfdctl.h b/bfdd/bfdctl.h
index 3cb2fba49..e1cff9a31 100644
--- a/bfdd/bfdctl.h
+++ b/bfdd/bfdctl.h
@@ -84,6 +84,9 @@ struct bfd_peer_cfg {
 	bool bpc_has_echointerval;
 	uint64_t bpc_echointerval;
 
+	bool bpc_has_minimum_ttl;
+	uint8_t bpc_minimum_ttl;
+
 	bool bpc_echo;
 	bool bpc_createonly;
 	bool bpc_shutdown;
diff --git a/bfdd/bfdd_cli.c b/bfdd/bfdd_cli.c
index e70354de0..058ce7d1f 100644
--- a/bfdd/bfdd_cli.c
+++ b/bfdd/bfdd_cli.c
@@ -287,6 +287,42 @@ void bfd_cli_show_passive(struct vty *vty, struct lyd_node *dnode,
 }
 
 DEFPY_YANG(
+	bfd_peer_minimum_ttl, bfd_peer_minimum_ttl_cmd,
+	"[no] minimum-ttl (1-254)$ttl",
+	NO_STR
+	"Expect packets with at least this TTL\n"
+	"Minimum TTL expected\n")
+{
+	if (no)
+		nb_cli_enqueue_change(vty, "./minimum-ttl", NB_OP_DESTROY,
+				      NULL);
+	else
+		nb_cli_enqueue_change(vty, "./minimum-ttl", NB_OP_MODIFY,
+				      ttl_str);
+	return nb_cli_apply_changes(vty, NULL);
+}
+
+DEFPY_YANG(
+	no_bfd_peer_minimum_ttl, no_bfd_peer_minimum_ttl_cmd,
+	"no minimum-ttl",
+	NO_STR
+	"Expect packets with at least this TTL\n")
+{
+	nb_cli_enqueue_change(vty, "./minimum-ttl", NB_OP_DESTROY, NULL);
+	return nb_cli_apply_changes(vty, NULL);
+}
+
+void bfd_cli_show_minimum_ttl(struct vty *vty, struct lyd_node *dnode,
+			      bool show_defaults)
+{
+	if (show_defaults)
+		vty_out(vty, "  minimum-ttl 254\n");
+	else
+		vty_out(vty, "  minimum-ttl %s\n",
+			yang_dnode_get_string(dnode, NULL));
+}
+
+DEFPY_YANG(
 	bfd_peer_mult, bfd_peer_mult_cmd,
 	"detect-multiplier (2-255)$multiplier",
 	"Configure peer detection multiplier\n"
@@ -488,6 +524,17 @@ ALIAS_YANG(bfd_peer_passive, bfd_profile_passive_cmd,
       NO_STR
       "Don't attempt to start sessions\n")
 
+ALIAS_YANG(bfd_peer_minimum_ttl, bfd_profile_minimum_ttl_cmd,
+      "[no] minimum-ttl (1-254)$ttl",
+      NO_STR
+      "Expect packets with at least this TTL\n"
+      "Minimum TTL expected\n")
+
+ALIAS_YANG(no_bfd_peer_minimum_ttl, no_bfd_profile_minimum_ttl_cmd,
+      "no minimum-ttl",
+      NO_STR
+      "Expect packets with at least this TTL\n")
+
 ALIAS_YANG(bfd_peer_echo, bfd_profile_echo_cmd,
       "[no] echo-mode",
       NO_STR
@@ -557,6 +604,8 @@ bfdd_cli_init(void)
 	install_element(BFD_PEER_NODE, &bfd_peer_echo_interval_cmd);
 	install_element(BFD_PEER_NODE, &bfd_peer_profile_cmd);
 	install_element(BFD_PEER_NODE, &bfd_peer_passive_cmd);
+	install_element(BFD_PEER_NODE, &bfd_peer_minimum_ttl_cmd);
+	install_element(BFD_PEER_NODE, &no_bfd_peer_minimum_ttl_cmd);
 
 	/* Profile commands. */
 	cmd_variable_handler_register(bfd_vars);
@@ -574,4 +623,6 @@ bfdd_cli_init(void)
 	install_element(BFD_PROFILE_NODE, &bfd_profile_echo_cmd);
 	install_element(BFD_PROFILE_NODE, &bfd_profile_echo_interval_cmd);
 	install_element(BFD_PROFILE_NODE, &bfd_profile_passive_cmd);
+	install_element(BFD_PROFILE_NODE, &bfd_profile_minimum_ttl_cmd);
+	install_element(BFD_PROFILE_NODE, &no_bfd_profile_minimum_ttl_cmd);
 }
diff --git a/bfdd/bfdd_nb.c b/bfdd/bfdd_nb.c
index cf063f82f..64ba3cf81 100644
--- a/bfdd/bfdd_nb.c
+++ b/bfdd/bfdd_nb.c
@@ -84,6 +84,14 @@ const struct frr_yang_module_info frr_bfdd_info = {
 				.cli_show = bfd_cli_show_passive,
                         }
                 },
+		{
+			.xpath = "/frr-bfdd:bfdd/bfd/profile/minimum-ttl",
+			.cbs = {
+				.modify = bfdd_bfd_profile_minimum_ttl_modify,
+				.destroy = bfdd_bfd_profile_minimum_ttl_destroy,
+				.cli_show = bfd_cli_show_minimum_ttl,
+			}
+		},
                 {
                         .xpath = "/frr-bfdd:bfdd/bfd/profile/echo-mode",
                         .cbs = {
@@ -350,6 +358,14 @@ const struct frr_yang_module_info frr_bfdd_info = {
 			}
 		},
 		{
+			.xpath = "/frr-bfdd:bfdd/bfd/sessions/multi-hop/minimum-ttl",
+			.cbs = {
+				.modify = bfdd_bfd_sessions_multi_hop_minimum_ttl_modify,
+				.destroy = bfdd_bfd_sessions_multi_hop_minimum_ttl_destroy,
+				.cli_show = bfd_cli_show_minimum_ttl,
+			}
+		},
+		{
 			.xpath = "/frr-bfdd:bfdd/bfd/sessions/multi-hop/stats/local-discriminator",
 			.cbs = {
 				.get_elem = bfdd_bfd_sessions_single_hop_stats_local_discriminator_get_elem,
diff --git a/bfdd/bfdd_nb.h b/bfdd/bfdd_nb.h
index ec467f357..fbd557b6b 100644
--- a/bfdd/bfdd_nb.h
+++ b/bfdd/bfdd_nb.h
@@ -38,6 +38,8 @@ int bfdd_bfd_profile_required_receive_interval_modify(
 	struct nb_cb_modify_args *args);
 int bfdd_bfd_profile_administrative_down_modify(struct nb_cb_modify_args *args);
 int bfdd_bfd_profile_passive_mode_modify(struct nb_cb_modify_args *args);
+int bfdd_bfd_profile_minimum_ttl_modify(struct nb_cb_modify_args *args);
+int bfdd_bfd_profile_minimum_ttl_destroy(struct nb_cb_destroy_args *args);
 int bfdd_bfd_profile_echo_mode_modify(struct nb_cb_modify_args *args);
 int bfdd_bfd_profile_desired_echo_transmission_interval_modify(
 	struct nb_cb_modify_args *args);
@@ -134,6 +136,10 @@ int bfdd_bfd_sessions_multi_hop_required_receive_interval_modify(
 	struct nb_cb_modify_args *args);
 int bfdd_bfd_sessions_multi_hop_administrative_down_modify(
 	struct nb_cb_modify_args *args);
+int bfdd_bfd_sessions_multi_hop_minimum_ttl_modify(
+	struct nb_cb_modify_args *args);
+int bfdd_bfd_sessions_multi_hop_minimum_ttl_destroy(
+	struct nb_cb_destroy_args *args);
 struct yang_data *
 bfdd_bfd_sessions_multi_hop_stats_local_discriminator_get_elem(
 	struct nb_cb_get_elem_args *args);
@@ -211,5 +217,7 @@ void bfd_cli_peer_profile_show(struct vty *vty, struct lyd_node *dnode,
 			       bool show_defaults);
 void bfd_cli_show_passive(struct vty *vty, struct lyd_node *dnode,
 			  bool show_defaults);
+void bfd_cli_show_minimum_ttl(struct vty *vty, struct lyd_node *dnode,
+			      bool show_defaults);
 
 #endif /* _FRR_BFDD_NB_H_ */
diff --git a/bfdd/bfdd_nb_config.c b/bfdd/bfdd_nb_config.c
index 527c6d83a..0046bc625 100644
--- a/bfdd/bfdd_nb_config.c
+++ b/bfdd/bfdd_nb_config.c
@@ -382,6 +382,42 @@ int bfdd_bfd_profile_passive_mode_modify(struct nb_cb_modify_args *args)
 }
 
 /*
+ * XPath: /frr-bfdd:bfdd/bfd/profile/minimum-ttl
+ */
+int bfdd_bfd_profile_minimum_ttl_modify(struct nb_cb_modify_args *args)
+{
+	struct bfd_profile *bp;
+	uint8_t minimum_ttl;
+
+	if (args->event != NB_EV_APPLY)
+		return NB_OK;
+
+	minimum_ttl = yang_dnode_get_uint8(args->dnode, NULL);
+	bp = nb_running_get_entry(args->dnode, NULL, true);
+	if (bp->minimum_ttl == minimum_ttl)
+		return NB_OK;
+
+	bp->minimum_ttl = minimum_ttl;
+	bfd_profile_update(bp);
+
+	return NB_OK;
+}
+
+int bfdd_bfd_profile_minimum_ttl_destroy(struct nb_cb_destroy_args *args)
+{
+	struct bfd_profile *bp;
+
+	if (args->event != NB_EV_APPLY)
+		return NB_OK;
+
+	bp = nb_running_get_entry(args->dnode, NULL, true);
+	bp->minimum_ttl = BFD_DEF_MHOP_TTL;
+	bfd_profile_update(bp);
+
+	return NB_OK;
+}
+
+/*
  * XPath: /frr-bfdd:bfdd/bfd/profile/echo-mode
  */
 int bfdd_bfd_profile_echo_mode_modify(struct nb_cb_modify_args *args)
@@ -739,3 +775,54 @@ int bfdd_bfd_sessions_multi_hop_destroy(struct nb_cb_destroy_args *args)
 {
 	return bfd_session_destroy(args->event, args->dnode, true);
 }
+
+/*
+ * XPath: /frr-bfdd:bfdd/bfd/sessions/multi-hop/minimum-ttl
+ */
+int bfdd_bfd_sessions_multi_hop_minimum_ttl_modify(
+	struct nb_cb_modify_args *args)
+{
+	struct bfd_session *bs;
+
+	switch (args->event) {
+	case NB_EV_VALIDATE:
+	case NB_EV_PREPARE:
+		return NB_OK;
+
+	case NB_EV_APPLY:
+		break;
+
+	case NB_EV_ABORT:
+		return NB_OK;
+	}
+
+	bs = nb_running_get_entry(args->dnode, NULL, true);
+	bs->peer_profile.minimum_ttl = yang_dnode_get_uint8(args->dnode, NULL);
+	bfd_session_apply(bs);
+
+	return NB_OK;
+}
+
+int bfdd_bfd_sessions_multi_hop_minimum_ttl_destroy(
+	struct nb_cb_destroy_args *args)
+{
+	struct bfd_session *bs;
+
+	switch (args->event) {
+	case NB_EV_VALIDATE:
+	case NB_EV_PREPARE:
+		return NB_OK;
+
+	case NB_EV_APPLY:
+		break;
+
+	case NB_EV_ABORT:
+		return NB_OK;
+	}
+
+	bs = nb_running_get_entry(args->dnode, NULL, true);
+	bs->peer_profile.minimum_ttl = BFD_DEF_MHOP_TTL;
+	bfd_session_apply(bs);
+
+	return NB_OK;
+}
diff --git a/bfdd/bfdd_vty.c b/bfdd/bfdd_vty.c
index a532b76f0..a3f1638e5 100644
--- a/bfdd/bfdd_vty.c
+++ b/bfdd/bfdd_vty.c
@@ -115,6 +115,8 @@ static void _display_peer(struct vty *vty, struct bfd_session *bs)
 		vty_out(vty, "\t\tPassive mode\n");
 	else
 		vty_out(vty, "\t\tActive mode\n");
+	if (CHECK_FLAG(bs->flags, BFD_SESS_FLAG_MH))
+		vty_out(vty, "\t\tMinimum TTL: %d\n", bs->mh_ttl);
 
 	vty_out(vty, "\t\tStatus: ");
 	switch (bs->ses_state) {
@@ -209,6 +211,8 @@ static struct json_object *__display_peer_json(struct bfd_session *bs)
 	json_object_int_add(jo, "remote-id", bs->discrs.remote_discr);
 	json_object_boolean_add(jo, "passive-mode",
 				CHECK_FLAG(bs->flags, BFD_SESS_FLAG_PASSIVE));
+	if (CHECK_FLAG(bs->flags, BFD_SESS_FLAG_MH))
+		json_object_int_add(jo, "minimum-ttl", bs->mh_ttl);
 
 	switch (bs->ses_state) {
 	case PTM_BFD_ADM_DOWN:
diff --git a/bfdd/ptm_adapter.c b/bfdd/ptm_adapter.c
index 8134807a1..48e55bce3 100644
--- a/bfdd/ptm_adapter.c
+++ b/bfdd/ptm_adapter.c
@@ -303,7 +303,6 @@ static int _ptm_msg_read(struct stream *msg, int command, vrf_id_t vrf_id,
 			 struct bfd_peer_cfg *bpc, struct ptm_client **pc)
 {
 	uint32_t pid;
-	uint8_t ttl __attribute__((unused));
 	size_t ifnamelen;
 
 	/*
@@ -375,7 +374,18 @@ static int _ptm_msg_read(struct stream *msg, int command, vrf_id_t vrf_id,
 	if (bpc->bpc_mhop) {
 		/* Read multihop source address and TTL. */
 		_ptm_msg_read_address(msg, &bpc->bpc_local);
-		STREAM_GETC(msg, ttl);
+		STREAM_GETC(msg, bpc->bpc_minimum_ttl);
+		if (bpc->bpc_minimum_ttl >= BFD_TTL_VAL
+		    || bpc->bpc_minimum_ttl == 0) {
+			zlog_warn("%s: received invalid TTL configuration %d",
+				  __func__, bpc->bpc_has_minimum_ttl);
+			bpc->bpc_minimum_ttl = BFD_DEF_MHOP_TTL;
+			bpc->bpc_has_minimum_ttl = false;
+		} else {
+			bpc->bpc_minimum_ttl =
+				(BFD_TTL_VAL + 1) - bpc->bpc_minimum_ttl;
+			bpc->bpc_has_minimum_ttl = true;
+		}
 	} else {
 		/* If target is IPv6, then we must obtain local address. */
 		if (bpc->bpc_ipv4 == false)