bgpd: add set as-path exclude acl-list command

A route-map applied on incoming BGP updates is not able
to replace an unwanted as segments by another one.
unwanted as segment are based on an AS path access-list.

The below configuration illustrates the case:

router bgp 65001

address-family ipv4 unicast
 neighbor 192.168.1.2 route-map rule_2 in
exit-address-family

bgp as-path access-list RULE permit ^65

route-map rule_2 permit 10
 set as-path replace as-path-access-list RULE 6000

```
BGP routing table entry for 10.10.10.10/32, version 13
Paths: (1 available, best sonic-net#1, table default)
  Advertised to non peer-group peers:
  192.168.10.65
  65000 1 2 3 123
    192.168.10.65 from 192.168.10.65 (10.10.10.11)
      Origin IGP, metric 0, valid, external, best (First path received)
```

After:

```
do show ip bgp 10.10.10.10/32
BGP routing table entry for 10.10.10.10/32, version 15
    Paths: (1 available, best sonic-net#1, table default)
      Advertised to non peer-group peers:
      192.168.10.65
      6000 1 2 3 123
        192.168.10.65 from 192.168.10.65 (10.10.10.11)
          Origin IGP, metric 0, valid, external, best (First path
          received)
```

Signed-off-by: Francois Dumontet <francois.dumontet@6wind.com>

bgpd/bgp_aspath.c

@@ -1231,6 +1231,46 @@ bool aspath_private_as_check(struct aspath *aspath)
 	return true;
 }
 
+/* Replace all ASN instances of the regex rule with our own ASN  */
+struct aspath *aspath_replace_regex_asn(struct aspath *aspath,
+					struct as_list *acl_list, as_t our_asn)
+{
+	struct aspath *new;
+	struct assegment *cur_seg;
+	struct as_list *cur_as_list;
+	struct as_filter *cur_as_filter;
+	char str_buf[ASPATH_STR_DEFAULT_LEN];
+	uint32_t i;
+
+	new = aspath_dup(aspath);
+	cur_seg = new->segments;
+
+	while (cur_seg) {
+		cur_as_list = acl_list;
+		while (cur_as_list) {
+			cur_as_filter = cur_as_list->head;
+			while (cur_as_filter) {
+				for (i = 0; i < cur_seg->length; i++) {
+					snprintfrr(str_buf,
+						   ASPATH_STR_DEFAULT_LEN,
+						   ASN_FORMAT(new->asnotation),
+						   &cur_seg->as[i]);
+					if (!regexec(cur_as_filter->reg,
+						     str_buf, 0, NULL, 0))
+						cur_seg->as[i] = our_asn;
+				}
+				cur_as_filter = cur_as_filter->next;
+			}
+			cur_as_list = cur_as_list->next;
+		}
+		cur_seg = cur_seg->next;
+	}
+
+	aspath_str_update(new, false);
+	return new;
+}
+
+
 /* Replace all instances of the target ASN with our own ASN */
 struct aspath *aspath_replace_specific_asn(struct aspath *aspath,
 					   as_t target_asn, as_t our_asn)

bgpd/bgp_aspath.h

@@ -107,6 +107,9 @@ extern unsigned int aspath_get_last_as(struct aspath *aspath);
 extern int aspath_loop_check(struct aspath *aspath, as_t asno);
 extern int aspath_loop_check_confed(struct aspath *aspath, as_t asno);
 extern bool aspath_private_as_check(struct aspath *aspath);
+extern struct aspath *aspath_replace_regex_asn(struct aspath *aspath,
+					       struct as_list *acl_list,
+					       as_t our_asn);
 extern struct aspath *aspath_replace_specific_asn(struct aspath *aspath,
 						  as_t target_asn,
 						  as_t our_asn);

bgpd/bgp_routemap.c

@@ -2410,18 +2410,63 @@ route_set_aspath_replace(void *rule, const struct prefix *dummy, void *object)
 	as_t configured_asn;
 	char *buf;
 	char src_asn[ASN_STRING_MAX_SIZE];
+	char *acl_list_name = NULL;
+	uint32_t acl_list_name_len = 0;
+	char *buf_acl_name = NULL;
+	static const char asp_acl[] = "as-path-access-list";
+	struct as_list *aspath_acl = NULL;
 
 	if (path->peer->sort != BGP_PEER_EBGP) {
 		zlog_warn(
 			"`set as-path replace` is supported only for EBGP peers");
-		return RMAP_NOOP;
+		goto end_ko;
 	}
 
 	buf = strchr(replace, ' ');
 	if (!buf) {
 		configured_asn = path->peer->change_local_as
 					 ? path->peer->change_local_as
 					 : path->peer->local_as;
+	} else if (!strncmp(replace, asp_acl, strlen(asp_acl))) {
+		/* its as-path-acl-list command get the access list name */
+		while (*buf == ' ')
+			buf++;
+		buf_acl_name = buf;
+		buf = strchr(buf_acl_name, ' ');
+		if (buf)
+			acl_list_name_len = buf - buf_acl_name;
+		else
+			acl_list_name_len = strlen(buf_acl_name);
+
+		buf_acl_name[acl_list_name_len] = 0;
+		/* get the acl-list */
+		aspath_acl = as_list_lookup(buf_acl_name);
+		if (!aspath_acl) {
+			zlog_warn("`set as-path replace`, invalid as-path-access-list name: %s",
+				  buf_acl_name);
+			goto end_ko;
+		}
+		acl_list_name = XSTRDUP(MTYPE_TMP, buf_acl_name);
+		buf_acl_name[acl_list_name_len] = ' ';
+
+		if (!buf) {
+			configured_asn = path->peer->change_local_as
+						 ? path->peer->change_local_as
+						 : path->peer->local_as;
+		} else {
+			while (*buf == ' ')
+				buf++;
+			/* get the configured asn */
+			if (!asn_str2asn(buf, &configured_asn)) {
+				zlog_warn(
+					"`set as-path replace`, invalid configured AS %s",
+					buf);
+				goto end_ko;
+			}
+		}
+
+		replace = buf;
+
 	} else {
 		memcpy(src_asn, replace, (size_t)(buf - replace));
 		src_asn[(size_t)(buf - replace)] = '\0';
@@ -2431,30 +2476,44 @@ route_set_aspath_replace(void *rule, const struct prefix *dummy, void *object)
 			zlog_warn(
 				"`set as-path replace`, invalid configured AS %s",
 				buf);
-			return RMAP_NOOP;
+			goto end_ko;
 		}
 	}
 
-	if (!strmatch(replace, "any") && !asn_str2asn(replace, &replace_asn)) {
+	if (replace && !strmatch(replace, "any") &&
+	    !asn_str2asn(replace, &replace_asn)) {
 		zlog_warn("`set as-path replace`, invalid AS %s", replace);
-		return RMAP_NOOP;
+		goto end_ko;
 	}
 
 	if (path->attr->aspath->refcnt)
 		aspath_new = aspath_dup(path->attr->aspath);
 	else
 		aspath_new = path->attr->aspath;
 
-	if (strmatch(replace, "any")) {
+	if (aspath_acl) {
+		path->attr->aspath = aspath_replace_regex_asn(aspath_new,
+							      aspath_acl,
+							      configured_asn);
+	} else if (strmatch(replace, "any")) {
 		path->attr->aspath =
 			aspath_replace_all_asn(aspath_new, configured_asn);
-	} else
+	} else {
 		path->attr->aspath = aspath_replace_specific_asn(
 			aspath_new, replace_asn, configured_asn);
-
+	}
 	aspath_free(aspath_new);
 
+
+	if (acl_list_name)
+		XFREE(MTYPE_TMP, acl_list_name);
 	return RMAP_OKAY;
+
+end_ko:
+	if (acl_list_name)
+		XFREE(MTYPE_TMP, acl_list_name);
+	return RMAP_NOOP;
+
 }
 
 static const struct route_map_rule_cmd route_set_aspath_replace_cmd = {
@@ -6087,6 +6146,61 @@ DEFPY_YANG(no_set_aspath_replace_asn, no_set_aspath_replace_asn_cmd,
 	return nb_cli_apply_changes(vty, NULL);
 }
 
+DEFPY_YANG(
+	set_aspath_replace_access_list, set_aspath_replace_access_list_cmd,
+	"set as-path replace as-path-access-list AS_PATH_FILTER_NAME$aspath_filter_name [<ASNUM>$configured_asn]",
+	SET_STR
+	"Transform BGP AS-path attribute\n"
+	"Replace AS number to local or configured AS number\n"
+	"Specify an as path access list name\n"
+	"AS path access list name\n"
+	"Define the configured AS number\n")
+{
+	char *str;
+	const char *xpath =
+		"./set-action[action='frr-bgp-route-map:as-path-replace']";
+	char xpath_value[XPATH_MAXLEN];
+	as_t as_configured_value;
+	char replace_value[ASN_STRING_MAX_SIZE * 2];
+
+	if (configured_asn_str &&
+	    !asn_str2asn(configured_asn_str, &as_configured_value)) {
+		vty_out(vty, "%% Invalid AS configured value %s\n",
+			configured_asn_str);
+		return CMD_WARNING_CONFIG_FAILED;
+	}
+
+	str = argv_concat(argv, argc, 3);
+
+	nb_cli_enqueue_change(vty, xpath, NB_OP_CREATE, NULL);
+
+	snprintf(replace_value, sizeof(replace_value), "%s %s", aspath_filter_name, str);
+
+	snprintf(xpath_value, sizeof(xpath_value),
+		 "%s/rmap-set-action/frr-bgp-route-map:replace-as-path", xpath);
+	nb_cli_enqueue_change(vty, xpath_value, NB_OP_MODIFY, str);
+
+	return nb_cli_apply_changes(vty, NULL);
+}
+
+DEFPY_YANG(
+	no_set_aspath_replace_access_list, no_set_aspath_replace_access_list_cmd,
+	"no set as-path replace as-path-access-list [AS_PATH_FILTER_NAME] [<ASNUM>$configured_asn]",
+	NO_STR
+	SET_STR
+	"Transform BGP AS_PATH attribute\n"
+	"Replace AS number to local or configured AS number\n"
+	"Specify an as path access list name\n"
+	"AS path access list name\n"
+	"Define the configured AS number\n")
+{
+	const char *xpath =
+		"./set-action[action='frr-bgp-route-map:as-path-replace']";
+
+	nb_cli_enqueue_change(vty, xpath, NB_OP_DESTROY, NULL);
+	return nb_cli_apply_changes(vty, NULL);
+}
+
 DEFUN_YANG (no_set_aspath_prepend,
 	    no_set_aspath_prepend_cmd,
 	    "no set as-path prepend [ASNUM]",
@@ -7792,12 +7906,14 @@ void bgp_route_map_init(void)
 	install_element(RMAP_NODE, &set_aspath_exclude_all_cmd);
 	install_element(RMAP_NODE, &set_aspath_exclude_access_list_cmd);
 	install_element(RMAP_NODE, &set_aspath_replace_asn_cmd);
+	install_element(RMAP_NODE, &set_aspath_replace_access_list_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_prepend_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_prepend_lastas_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_exclude_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_exclude_all_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_exclude_access_list_cmd);
 	install_element(RMAP_NODE, &no_set_aspath_replace_asn_cmd);
+	install_element(RMAP_NODE, &no_set_aspath_replace_access_list_cmd);
 	install_element(RMAP_NODE, &set_origin_cmd);
 	install_element(RMAP_NODE, &no_set_origin_cmd);
 	install_element(RMAP_NODE, &set_atomic_aggregate_cmd);