net/sctp: fix a null dereference in sctp_disposition sctp_sf_do_5_1D_ce()

If new_asoc->peer.adaptation_ind=0 and sctp_ulpevent_make_authkey=0
and sctp_ulpevent_make_authkey() returns 0, then the variable
ai_ev remains zero and the zero will be dereferenced
in the sctp_ulpevent_free() function.

Signed-off-by: Alexandr Sapozhnikov <alsp705@gmail.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Fixes: 30f6ebf ("sctp: add SCTP_AUTH_NO_AUTH type for AUTHENTICATION_EVENT")
Link: https://patch.msgid.link/20251002091448.11-1-alsp705@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Alexandr Sapozhnikov

net/sctp/sm_statefuns.c

@@ -886,7 +886,8 @@ enum sctp_disposition sctp_sf_do_5_1D_ce(struct net *net,
 	return SCTP_DISPOSITION_CONSUME;
 
 nomem_authev:
-	sctp_ulpevent_free(ai_ev);
+	if (ai_ev)
+		sctp_ulpevent_free(ai_ev);
 nomem_aiev:
 	sctp_ulpevent_free(ev);
 nomem_ev: