isisd: fix crash at flex-algo without mpls-te

Fix crash when flex-algo is configured and mpls-te is disabled.

> interface eth0
>  ip router isis 1
> !
> router isis 1
>  flex-algo 129
>   dataplane sr-mpls
>   advertise-definition

> #0  __pthread_kill_implementation (no_tid=0, signo=11, threadid=140486233631168) at ./nptl/pthread_kill.c:44
> #1  __pthread_kill_internal (signo=11, threadid=140486233631168) at ./nptl/pthread_kill.c:78
> #2  __GI___pthread_kill (threadid=140486233631168, signo=signo@entry=11) at ./nptl/pthread_kill.c:89
> #3  0x00007fc5802e9476 in __GI_raise (sig=11) at ../sysdeps/posix/raise.c:26
> #4  0x00007fc58076021f in core_handler (signo=11, siginfo=0x7ffd38d42470, context=0x7ffd38d42340) at lib/sigevent.c:248
> #5  <signal handler called>
> #6  0x000055c527f798c9 in isis_link_params_update_asla (circuit=0x55c52aaed3c0, ifp=0x55c52a1044e0) at isisd/isis_te.c:176
> #7  0x000055c527fb29da in isis_instance_flex_algo_create (args=0x7ffd38d43120) at isisd/isis_nb_config.c:2875
> #8  0x00007fc58072655b in nb_callback_create (context=0x55c52ab1d2f0, nb_node=0x55c529f72950, event=NB_EV_APPLY, dnode=0x55c52ab06230, resource=0x55c52ab189f8, errmsg=0x7ffd38d43750 "",
>     errmsg_len=8192) at lib/northbound.c:1262
> #9  0x00007fc580727625 in nb_callback_configuration (context=0x55c52ab1d2f0, event=NB_EV_APPLY, change=0x55c52ab189c0, errmsg=0x7ffd38d43750 "", errmsg_len=8192) at lib/northbound.c:1662
> #10 0x00007fc580727c39 in nb_transaction_process (event=NB_EV_APPLY, transaction=0x55c52ab1d2f0, errmsg=0x7ffd38d43750 "", errmsg_len=8192) at lib/northbound.c:1794
> #11 0x00007fc580725f77 in nb_candidate_commit_apply (transaction=0x55c52ab1d2f0, save_transaction=true, transaction_id=0x0, errmsg=0x7ffd38d43750 "", errmsg_len=8192)
>     at lib/northbound.c:1131
> #12 0x00007fc5807260d1 in nb_candidate_commit (context=..., candidate=0x55c529f0a730, save_transaction=true, comment=0x0, transaction_id=0x0, errmsg=0x7ffd38d43750 "", errmsg_len=8192)
>     at lib/northbound.c:1164
> #13 0x00007fc58072d220 in nb_cli_classic_commit (vty=0x55c52a0fc6b0) at lib/northbound_cli.c:51
> #14 0x00007fc58072d839 in nb_cli_apply_changes_internal (vty=0x55c52a0fc6b0,
>     xpath_base=0x7ffd38d477f0 "/frr-isisd:isis/instance[area-tag='1'][vrf='default']/flex-algos/flex-algo[flex-algo='129']", clear_pending=false) at lib/northbound_cli.c:178
> #15 0x00007fc58072dbcf in nb_cli_apply_changes (vty=0x55c52a0fc6b0, xpath_base_fmt=0x55c528014de0 "./flex-algos/flex-algo[flex-algo='%ld']") at lib/northbound_cli.c:234
> #16 0x000055c527fd3403 in flex_algo_magic (self=0x55c52804f1a0 <flex_algo_cmd>, vty=0x55c52a0fc6b0, argc=2, argv=0x55c52ab00ec0, algorithm=129, algorithm_str=0x55c52ab120d0 "129")
>     at isisd/isis_cli.c:3752
> #17 0x000055c527fc97cb in flex_algo (self=0x55c52804f1a0 <flex_algo_cmd>, vty=0x55c52a0fc6b0, argc=2, argv=0x55c52ab00ec0) at ./isisd/isis_cli_clippy.c:6445
> #18 0x00007fc5806b9abc in cmd_execute_command_real (vline=0x55c52aaf78f0, vty=0x55c52a0fc6b0, cmd=0x0, up_level=0) at lib/command.c:984
> #19 0x00007fc5806b9c35 in cmd_execute_command (vline=0x55c52aaf78f0, vty=0x55c52a0fc6b0, cmd=0x0, vtysh=0) at lib/command.c:1043
> #20 0x00007fc5806ba1e5 in cmd_execute (vty=0x55c52a0fc6b0, cmd=0x55c52aae6bd0 "flex-algo 129\n", matched=0x0, vtysh=0) at lib/command.c:1209
> #21 0x00007fc580782ae1 in vty_command (vty=0x55c52a0fc6b0, buf=0x55c52aae6bd0 "flex-algo 129\n") at lib/vty.c:615
> #22 0x00007fc580784a05 in vty_execute (vty=0x55c52a0fc6b0) at lib/vty.c:1378
> #23 0x00007fc580787131 in vtysh_read (thread=0x7ffd38d4ab10) at lib/vty.c:2373
> #24 0x00007fc58077b605 in event_call (thread=0x7ffd38d4ab10) at lib/event.c:2011
> #25 0x00007fc5806f8976 in frr_run (master=0x55c529df9b30) at lib/libfrr.c:1212
> #26 0x000055c527f301bc in main (argc=5, argv=0x7ffd38d4ad58, envp=0x7ffd38d4ad88) at isisd/isis_main.c:350
> (gdb) f 6
> #6  0x000055c527f798c9 in isis_link_params_update_asla (circuit=0x55c52aaed3c0, ifp=0x55c52a1044e0) at isisd/isis_te.c:176
> 176                     list_delete_all_node(ext->aslas);
> (gdb) p ext
> $1 = (struct isis_ext_subtlvs *) 0x0

Fixes: ae27101 ("isisd: fix building asla at first flex-algo config")
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>
(cherry picked from commit cd81d28)

isisd/isis_te.c

@@ -172,6 +172,10 @@ static void isis_link_params_update_asla(struct isis_circuit *circuit,
 	struct isis_ext_subtlvs *ext = circuit->ext;
 	int i;
 
+	if (!ext)
+		/* no extended subTLVs - nothing to update */
+		return;
+
 	if (!HAS_LINK_PARAMS(ifp)) {
 		list_delete_all_node(ext->aslas);
 		return;