network: drop pending requests when a DHCP lease is lost or a client is stopped

When a DHCP lease is lost or a client is stopped, there may exist
requests not processed yet. We need to cancel them, otherwise an
address or route requested by the lost lease may be configured later.

src/network/networkd-dhcp-prefix-delegation.c

@@ -271,6 +271,10 @@ int dhcp_pd_remove(Link *link, bool only_marked) {
                 }
         }
 
+        if (!only_marked)
+                /* Also drop pending requests when the lease is lost or the client is stopped. */
+                RET_GATHER(ret, link_drop_requests(link, NETWORK_CONFIG_SOURCE_DHCP_PD));
+
         return ret;
 }
 

src/network/networkd-dhcp4.c

@@ -272,6 +272,10 @@ static int dhcp4_remove_address_and_routes(Link *link, bool only_marked) {
                 RET_GATHER(ret, address_remove_and_cancel(address, link));
         }
 
+        if (!only_marked)
+                /* Also drop pending requests when the lease is lost or the client is stopped. */
+                RET_GATHER(ret, link_drop_requests(link, NETWORK_CONFIG_SOURCE_DHCP4));
+
         return ret;
 }
 

src/network/networkd-dhcp6.c

@@ -83,6 +83,10 @@ static int dhcp6_remove(Link *link, bool only_marked) {
                 RET_GATHER(ret, address_remove_and_cancel(address, link));
         }
 
+        if (!only_marked)
+                /* Also drop pending requests when the lease is lost or the client is stopped. */
+                RET_GATHER(ret, link_drop_requests(link, NETWORK_CONFIG_SOURCE_DHCP6));
+
         return ret;
 }
 

src/network/networkd-ndisc.c

@@ -3194,6 +3194,9 @@ int ndisc_stop(Link *link) {
 void ndisc_flush(Link *link) {
         assert(link);
 
+        /* First, drop pending requests. */
+        (void) link_drop_requests(link, NETWORK_CONFIG_SOURCE_NDISC);
+
         /* Remove all addresses, routes, RDNSS, DNSSL, DNR, and Captive Portal entries, without exception. */
         (void) ndisc_drop_outdated(link, /* router= */ NULL, /* timestamp_usec= */ USEC_INFINITY);
         (void) ndisc_drop_redirect(link, /* router= */ NULL);