bgpd: fix no bgp as-path access-list issue

router bgp 65001
 no bgp ebgp-requires-policy
 neighbor 192.168.1.2 remote-as external
 neighbor 192.168.1.2 timers 3 10
 address-family ipv4 unicast
  neighbor 192.168.1.2 route-map r2 in
 exit-address-family
!
ip prefix-list p1 seq 5 permit 172.16.255.31/32
!
route-map r2 permit 10
 match ip address prefix-list p1
 set as-path exclude 65003
route-map r2 permit 20
 set as-path exclude all
!

we make the following commands

bgp as-path access-list FIRST permit ^65
bgp as-path access-list SECOND permit 2
 route-map r2 permit 6
  set as-path exclude as-path-access-list SECOND

and then

no bgp as-path access-list SECOND permit 2
clear bgp *

we have the following crash in bgp

               Stack trace of thread 536083:
                #0  0x00007f87f8aacfe1 raise (libpthread.so.0 + 0x12fe1)
                #1  0x00007f87f8cf6870 core_handler (libfrr.so.0 +
		    0xf6870)
                #2  0x00007f87f8aad140 __restore_rt (libpthread.so.0 +
		    0x13140)
                #3  0x00007f87f89a5122 __GI___regexec (libc.so.6 +
		    0xdf122)
                #4  0x000055d7f198b4a7 aspath_filter_exclude_acl (bgpd +
		    0x2054a7)
                #5  0x000055d7f1902187 route_set_aspath_exclude (bgpd +
		    0x17c187)
                #6  0x00007f87f8ce54b0 route_map_apply_ext (libfrr.so.0
		    + 0xe54b0)
                #7  0x000055d7f18da925 bgp_input_modifier (bgpd +
		    0x154925)
                #8  0x000055d7f18e0647 bgp_update (bgpd + 0x15a647)
                #9  0x000055d7f18e4772 bgp_nlri_parse_ip (bgpd +
		    0x15e772)
                #10 0x000055d7f18c38ae bgp_nlri_parse (bgpd + 0x13d8ae)
                #11 0x000055d7f18c6b7a bgp_update_receive (bgpd +
		    0x140b7a)
                #12 0x000055d7f18c8ff3 bgp_process_packet (bgpd +
		    0x142ff3)
                #13 0x00007f87f8d0dce0 thread_call (libfrr.so.0 +
		    0x10dce0)
                #14 0x00007f87f8cacb28 frr_run (libfrr.so.0 + 0xacb28)
                #15 0x000055d7f18435da main (bgpd + 0xbd5da)
                #16 0x00007f87f88e9d0a __libc_start_main (libc.so.6 +
		    0x23d0a)
                #17 0x000055d7f18415fa _start (bgpd + 0xbb5fa)

analysis

crash is due to the fact that there were always a pointer from
as-path exclude to deleted as-path access list.

fix
we add a backpointer mechanism to manage the dependency beetween
as-path access-list  and aspath exclude.

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

bgpd/bgp_aspath.h

@@ -65,6 +65,14 @@ struct aspath {
 
 #define ASPATH_STR_DEFAULT_LEN 32
 
+/* `set as-path exclude ASn' */
+struct aspath_exclude {
+	struct aspath *aspath;
+	bool exclude_all;
+	char *exclude_aspath_acl_name;
+	struct as_list *exclude_aspath_acl;
+};
+
 /* Prototypes. */
 extern void aspath_init(void);
 extern void aspath_finish(void);

bgpd/bgp_filter.c

@@ -205,8 +205,17 @@ static struct as_list *as_list_new(void)
 
 static void as_list_free(struct as_list *aslist)
 {
-	XFREE(MTYPE_AS_STR, aslist->name);
-	XFREE(MTYPE_AS_LIST, aslist);
+	struct aspath_exclude_list *cur_bp = aslist->exclude_list;
+	struct aspath_exclude_list *next_bp = NULL;
+
+	while (cur_bp) {
+		next_bp = cur_bp->next;
+		XFREE(MTYPE_ROUTE_MAP_COMPILED, cur_bp);
+		cur_bp = next_bp;
+	}
+
+	XFREE (MTYPE_AS_STR, aslist->name);
+	XFREE (MTYPE_AS_LIST, aslist);
 }
 
 /* Insert new AS list to list of as_list.  Each as_list is sorted by
@@ -290,6 +299,7 @@ static void as_list_delete(struct as_list *aslist)
 {
 	struct as_list_list *list;
 	struct as_filter *filter, *next;
+	struct aspath_exclude_list *cur_bp;
 
 	for (filter = aslist->head; filter; filter = next) {
 		next = filter->next;
@@ -308,6 +318,12 @@ static void as_list_delete(struct as_list *aslist)
 	else
 		list->head = aslist->next;
 
+	cur_bp = aslist->exclude_list;
+	while (cur_bp) {
+		cur_bp->bp_as_excl->exclude_aspath_acl = NULL;
+		cur_bp = cur_bp->next;
+	}
+
 	as_list_free(aslist);
 }
 

bgpd/bgp_filter.h

@@ -25,6 +25,11 @@ struct as_filter {
 	int64_t seq;
 };
 
+struct aspath_exclude_list {
+	struct aspath_exclude_list *next;
+	struct aspath_exclude *bp_as_excl;
+};
+
 /* AS path filter list. */
 struct as_list {
 	char *name;
@@ -34,6 +39,7 @@ struct as_list {
 
 	struct as_filter *head;
 	struct as_filter *tail;
+	struct aspath_exclude_list *exclude_list;
 };
 
 

bgpd/bgp_routemap.c

@@ -2323,17 +2323,10 @@ static const struct route_map_rule_cmd route_set_aspath_prepend_cmd = {
 	route_set_aspath_prepend_free,
 };
 
-/* `set as-path exclude ASn' */
-struct aspath_exclude {
-	struct aspath *aspath;
-	bool exclude_all;
-	char *exclude_aspath_acl_name;
-	struct as_list *exclude_aspath_acl;
-};
-
 static void *route_aspath_exclude_compile(const char *arg)
 {
 	struct aspath_exclude *ase;
+	struct aspath_exclude_list *ael;
 	const char *str = arg;
 	static const char asp_acl[] = "as-path-access-list";
 
@@ -2348,16 +2341,41 @@ static void *route_aspath_exclude_compile(const char *arg)
 		ase->exclude_aspath_acl = as_list_lookup(str);
 	} else
 		ase->aspath = aspath_str2aspath(str, bgp_get_asnotation(NULL));
+
+	if (ase->exclude_aspath_acl) {
+		ael = XCALLOC(MTYPE_ROUTE_MAP_COMPILED,
+				sizeof(struct aspath_exclude_list));
+		ael->bp_as_excl = ase;
+		ael->next = ase->exclude_aspath_acl->exclude_list;
+		ase->exclude_aspath_acl->exclude_list = ael;
+	}
+
 	return ase;
 }
 
 static void route_aspath_exclude_free(void *rule)
 {
 	struct aspath_exclude *ase = rule;
+	struct aspath_exclude_list *cur_ael = NULL;
+	struct aspath_exclude_list *prev_ael = NULL;
 
 	aspath_free(ase->aspath);
 	if (ase->exclude_aspath_acl_name)
 		XFREE(MTYPE_TMP, ase->exclude_aspath_acl_name);
+	if (ase->exclude_aspath_acl)
+		cur_ael = ase->exclude_aspath_acl->exclude_list;
+	while (cur_ael) {
+		if (cur_ael->bp_as_excl == ase) {
+			if (prev_ael)
+				prev_ael->next = cur_ael->next;
+			else
+				ase->exclude_aspath_acl->exclude_list = NULL;
+			XFREE(MTYPE_ROUTE_MAP_COMPILED, cur_ael);
+			break;
+		}
+		prev_ael = cur_ael;
+		cur_ael = cur_ael->next;
+	}
 	XFREE(MTYPE_ROUTE_MAP_COMPILED, ase);
 }