net: l2: ppp: Allow PPP to transtition ESTABLISH->DEAD

When remote peer have closed the PPP link normally, the
PPP stack on Zephyr side switches back to ESTABLISH phase
to be ready for next handshake.

When calling net_if_down() on the interface, it should not
try to initiate LCP link termination, but instead go directly
to DEAD phase.

See https://datatracker.ietf.org/doc/html/rfc1661#section-3.2

Signed-off-by: Seppo Takalo <[email protected]>

Author: SeppoTakalo

subsys/net/l2/ppp/fsm.c

@@ -53,6 +53,13 @@ struct net_if *ppp_fsm_iface(struct ppp_fsm *fsm)
 	return ctx->iface;
 }
 
+static bool ppp_fsm_is_dead(struct ppp_fsm *fsm)
+{
+	struct ppp_context *ctx = ppp_fsm_ctx(fsm);
+
+	return ctx->phase == PPP_DEAD;
+}
+
 static void fsm_send_configure_req(struct ppp_fsm *fsm, bool retransmit)
 {
 	struct net_pkt *pkt = NULL;
@@ -246,6 +253,10 @@ void ppp_fsm_close(struct ppp_fsm *fsm, const uint8_t *reason)
 
 	case PPP_STOPPING:
 		ppp_change_state(fsm, PPP_CLOSING);
+		if (ppp_fsm_is_dead(fsm)) {
+			fsm->retransmits = 0;
+			k_work_reschedule(&fsm->timer, K_NO_WAIT);
+		}
 		break;
 
 	default:

subsys/net/l2/ppp/lcp.c

@@ -189,7 +189,12 @@ static void lcp_open(struct ppp_context *ctx)
 static void lcp_close(struct ppp_context *ctx, const uint8_t *reason)
 {
 	if (ctx->phase != PPP_DEAD) {
-		ppp_change_phase(ctx, PPP_TERMINATE);
+		if (ctx->phase == PPP_ESTABLISH) {
+			/* Link is not established yet, so we can go directly to DEAD */
+			ppp_change_phase(ctx, PPP_DEAD);
+		} else {
+			ppp_change_phase(ctx, PPP_TERMINATE);
+		}
 	}
 
 	ppp_fsm_close(&ctx->lcp.fsm, reason);