Add support for RFC 2132 Message option in NAK handling

hooks/dhcpcd-run-hooks.8.in

@@ -124,6 +124,9 @@ dhcpcd's lease or state expired and it failed to obtain a new one.
 .It Dv NAK
 dhcpcd received a NAK from the DHCP server.
 This should be treated as EXPIRE.
+If the server included a Message option (RFC 2132 option 56),
+.Ev $message
+is set to that text.
 .It Dv RECONFIGURE
 dhcpcd has been instructed to reconfigure an interface.
 .It Dv ROUTERADVERT
@@ -158,6 +161,10 @@ the name of the interface.
 the protocol that triggered the event.
 .It Ev $reason
 as described above.
+.It Ev $message
+the RFC 2132 Message option (code 56) included with a
+.Dv NAK
+reason, if present.
 .It Ev $pid
 the pid of
 .Nm dhcpcd .

src/dhcp.c

@@ -3271,6 +3271,10 @@ dhcp_handledhcp(struct interface *ifp, struct bootp *bootp, size_t bootp_len,
 		if (state->state == DHS_INFORM) /* INFORM should not be NAKed */
 			return;
 		if (!(ifp->ctx->options & DHCPCD_TEST)) {
+			if (state->message)
+				free(state->message);
+			state->message = get_option_string(ifp->ctx, bootp,
+				bootp_len, DHO_MESSAGE);
 			dhcp_drop(ifp, "NAK");
 			dhcp_unlink(ifp->ctx, state->leasefile);
 		}
@@ -3914,6 +3918,7 @@ dhcp_free(struct interface *ifp)
 		free(state->new);
 		free(state->offer);
 		free(state->clientid);
+		free(state->message);
 		free(state);
 		ifp->if_data[IF_DATA_DHCP] = NULL;
 	}

src/dhcp.h

@@ -236,6 +236,7 @@ struct dhcp_state {
 #ifdef ARPING
 	ssize_t arping_index;
 #endif
+	char *message; /* RFC 2132 option 56 from DHCPv4 NAK */
 };
 
 #ifdef INET

src/script.c

@@ -470,6 +470,18 @@ make_env(struct dhcpcd_ctx *ctx, const struct interface *ifp,
 		if_up = false_str;
 		if_down = true_str;
 	}
+#ifdef INET
+	if (strcmp(reason, "NAK") == 0) {
+		struct dhcp_state *dstate = D_STATE(ifp);
+
+		if (dstate != NULL && dstate->message != NULL) {
+			if (efprintf(fp, "message=%s", dstate->message) == -1)
+				goto eexit;
+			free(dstate->message);
+			dstate->message = NULL;
+		}
+	}
+#endif
 	if (efprintf(fp, "if_up=%s", if_up) == -1)
 		goto eexit;
 	if (efprintf(fp, "if_down=%s", if_down) == -1)