net: dhcp: fix invalid timeout on send failure

If send_request() fails it would return UINT32_MAX as the next
timeout.  Callers pass the returned value to update_timeout_work
without validating it.  This has worked only because
update_timeout_work will not set a timeout if an existing timeout
would fire earlier, and the way the state is currently structured it
is likely there will be an existing timeout.  However, if work thread
retransmission from REQUESTING failed the timer would not be
rescheduled, causing the state machine to stop.

A more clean solution, which matches the behavior of send_discover(),
is to return the timeout for the next transmission even in the case
when the send fails.  The observed behavior is the same as if the
network, rather than the sender, failed to transport the request.

Signed-off-by: Peter Bigot <[email protected]>

Author: pabigot

subsys/net/ip/dhcpv4.c

@@ -297,7 +297,11 @@ static uint32_t dhcpv4_update_message_timeout(struct net_if_dhcpv4 *dhcpv4)
 	return timeout;
 }
 
-/* Prepare DHCPv4 Message request and send it to peer */
+/* Prepare DHCPv4 Message request and send it to peer.
+ *
+ * Returns the number of seconds until the next time-triggered event,
+ * or UINT32_MAX if the client is in an invalid state.
+ */
 static uint32_t dhcpv4_send_request(struct net_if *iface)
 {
 	const struct in_addr *server_addr = net_ipv4_broadcast_address();
@@ -306,7 +310,7 @@ static uint32_t dhcpv4_send_request(struct net_if *iface)
 	bool with_server_id = false;
 	bool with_requested_ip = false;
 	struct net_pkt *pkt = NULL;
-	uint32_t timeout;
+	uint32_t timeout = UINT32_MAX;
 
 	iface->config.dhcpv4.xid++;
 
@@ -346,6 +350,8 @@ static uint32_t dhcpv4_send_request(struct net_if *iface)
 		break;
 	}
 
+	timeout = dhcpv4_update_message_timeout(&iface->config.dhcpv4);
+
 	pkt = dhcpv4_create_message(iface, DHCPV4_MSG_TYPE_REQUEST,
 				    ciaddr, src_addr, server_addr,
 				    with_server_id, with_requested_ip);
@@ -357,8 +363,6 @@ static uint32_t dhcpv4_send_request(struct net_if *iface)
 		goto fail;
 	}
 
-	timeout = dhcpv4_update_message_timeout(&iface->config.dhcpv4);
-
 	NET_DBG("send request dst=%s xid=0x%x ciaddr=%s%s%s timeout=%us",
 		log_strdup(net_sprint_ipv4_addr(server_addr)),
 		iface->config.dhcpv4.xid,
@@ -375,7 +379,7 @@ static uint32_t dhcpv4_send_request(struct net_if *iface)
 		net_pkt_unref(pkt);
 	}
 
-	return UINT32_MAX;
+	return timeout;
 }
 
 /* Prepare DHCPv4 Discover message and broadcast it */