sd-ipv4ll: Add reference counting for IPv4LL

Similar to DHCP, the IPv4LL library user can decide to free the LL
client any time the callback is called. Guard against freeing the
LL client in the callback by introducing proper reference counting.

Also update code using the IPv4LL library to properly handle a
returned NULL from the notify and stop functions if the IPv4LL
client was freed.

3 files changed, 63 insertions, 28 deletions

diff --git a/src/libsystemd-network/sd-ipv4ll.c b/src/libsystemd-network/sd-ipv4ll.c
index 81fe85b68b..37cb802b63 100644
--- a/src/libsystemd-network/sd-ipv4ll.c
+++ b/src/libsystemd-network/sd-ipv4ll.c
@@ -26,6 +26,7 @@
 #include "util.h"
 #include "siphash24.h"
 #include "list.h"
+#include "refcnt.h"
 
 #include "ipv4ll-internal.h"
 #include "sd-ipv4ll.h"
@@ -65,6 +66,8 @@ typedef enum IPv4LLState {
 } IPv4LLState;
 
 struct sd_ipv4ll {
+        RefCount n_ref;
+
         IPv4LLState state;
         int index;
         int fd;
@@ -103,16 +106,19 @@ static void ipv4ll_set_state(sd_ipv4ll *ll, IPv4LLState st, int reset_counter) {
         }
 }
 
-static int ipv4ll_client_notify(sd_ipv4ll *ll, int event) {
+static sd_ipv4ll *ipv4ll_client_notify(sd_ipv4ll *ll, int event) {
         assert(ll);
 
-        if (ll->cb)
+        if (ll->cb) {
+                ll = sd_ipv4ll_ref(ll);
                 ll->cb(ll, event, ll->userdata);
+                ll = sd_ipv4ll_unref(ll);
+        }
 
-        return 0;
+        return ll;
 }
 
-static int ipv4ll_stop(sd_ipv4ll *ll, int event) {
+static sd_ipv4ll *ipv4ll_stop(sd_ipv4ll *ll, int event) {
         assert(ll);
 
         ll->receive_message = sd_event_source_unref(ll->receive_message);
@@ -120,15 +126,16 @@ static int ipv4ll_stop(sd_ipv4ll *ll, int event) {
 
         ll->timer = sd_event_source_unref(ll->timer);
 
-        ipv4ll_client_notify(ll, event);
-
-        ll->claimed_address = 0;
+        log_ipv4ll(ll, "STOPPED");
 
-        ipv4ll_set_state (ll, IPV4LL_STATE_INIT, 1);
+        ll = ipv4ll_client_notify(ll, event);
 
-        log_ipv4ll(ll, "STOPPED");
+        if (ll) {
+                ll->claimed_address = 0;
+                ipv4ll_set_state (ll, IPV4LL_STATE_INIT, 1);
+        }
 
-        return 0;
+        return ll;
 }
 
 static int ipv4ll_pick_address(sd_ipv4ll *ll, be32_t *address) {
@@ -256,7 +263,10 @@ static void ipv4ll_run_state_machine(sd_ipv4ll *ll, IPv4LLTrigger trigger, void
                 if (ll->iteration == 0) {
                         log_ipv4ll(ll, "ANNOUNCE");
                         ll->claimed_address = ll->address;
-                        r = ipv4ll_client_notify(ll, IPV4LL_EVENT_BIND);
+                        ll = ipv4ll_client_notify(ll, IPV4LL_EVENT_BIND);
+                        if (!ll)
+                                goto out;
+
                         ll->conflict = 0;
                 }
 
@@ -300,7 +310,10 @@ static void ipv4ll_run_state_machine(sd_ipv4ll *ll, IPv4LLTrigger trigger, void
 
                 if (conflicted) {
                         log_ipv4ll(ll, "CONFLICT");
-                        r = ipv4ll_client_notify(ll, IPV4LL_EVENT_CONFLICT);
+                        ll = ipv4ll_client_notify(ll, IPV4LL_EVENT_CONFLICT);
+                        if (!ll)
+                                goto out;
+
                         ll->claimed_address = 0;
 
                         /* Pick a new address */
@@ -341,7 +354,7 @@ static void ipv4ll_run_state_machine(sd_ipv4ll *ll, IPv4LLTrigger trigger, void
         }
 
 out:
-        if (r < 0)
+        if (r < 0 && ll)
                 ipv4ll_stop(ll, r);
 }
 
@@ -388,10 +401,13 @@ int sd_ipv4ll_set_mac(sd_ipv4ll *ll, const struct ether_addr *addr) {
         if (ll->state != IPV4LL_STATE_INIT) {
                 log_ipv4ll(ll, "Changing MAC address on running IPv4LL "
                            "client, restarting");
-                sd_ipv4ll_stop(ll);
+                ll = ipv4ll_stop(ll, IPV4LL_EVENT_STOP);
                 need_restart = true;
         }
 
+        if (!ll)
+                return 0;
+
         memcpy(&ll->mac_addr, addr, ETH_ALEN);
 
         if (need_restart)
@@ -555,23 +571,40 @@ out:
 }
 
 int sd_ipv4ll_stop(sd_ipv4ll *ll) {
-        return ipv4ll_stop(ll, IPV4LL_EVENT_STOP);
+        ipv4ll_stop(ll, IPV4LL_EVENT_STOP);
+
+        return 0;
 }
 
-void sd_ipv4ll_free (sd_ipv4ll *ll) {
-        if (!ll)
-                return;
+sd_ipv4ll *sd_ipv4ll_ref(sd_ipv4ll *ll) {
+        if (ll)
+                assert_se(REFCNT_INC(ll->n_ref) >= 2);
 
-        sd_ipv4ll_stop(ll);
-        sd_ipv4ll_detach_event(ll);
+        return ll;
+}
 
-        free(ll->random_data);
-        free(ll->random_data_state);
-        free(ll);
+sd_ipv4ll *sd_ipv4ll_unref(sd_ipv4ll *ll) {
+        if (ll && REFCNT_DEC(ll->n_ref) <= 0) {
+                ll->receive_message =
+                        sd_event_source_unref(ll->receive_message);
+                ll->fd = safe_close(ll->fd);
+
+                ll->timer = sd_event_source_unref(ll->timer);
+
+                sd_ipv4ll_detach_event(ll);
+
+                free(ll->random_data);
+                free(ll->random_data_state);
+                free(ll);
+
+                return NULL;
+        }
+
+        return ll;
 }
 
-DEFINE_TRIVIAL_CLEANUP_FUNC(sd_ipv4ll*, sd_ipv4ll_free);
-#define _cleanup_ipv4ll_free_ _cleanup_(sd_ipv4ll_freep)
+DEFINE_TRIVIAL_CLEANUP_FUNC(sd_ipv4ll*, sd_ipv4ll_unref);
+#define _cleanup_ipv4ll_free_ _cleanup_(sd_ipv4ll_unrefp)
 
 int sd_ipv4ll_new(sd_ipv4ll **ret) {
         _cleanup_ipv4ll_free_ sd_ipv4ll *ll = NULL;
@@ -582,6 +615,7 @@ int sd_ipv4ll_new(sd_ipv4ll **ret) {
         if (!ll)
                 return -ENOMEM;
 
+        ll->n_ref = REFCNT_INIT;
         ll->state = IPV4LL_STATE_INIT;
         ll->index = -1;
         ll->fd = -1;
diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index 2630b4625a..684e1e5d3d 100644
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -83,7 +83,7 @@ void link_free(Link *link) {
         sd_dhcp_client_unref(link->dhcp_client);
         sd_dhcp_lease_unref(link->dhcp_lease);
 
-        sd_ipv4ll_free(link->ipv4ll);
+        sd_ipv4ll_unref(link->ipv4ll);
 
         hashmap_remove(link->manager->links, &link->ifindex);
 
diff --git a/src/systemd/sd-ipv4ll.h b/src/systemd/sd-ipv4ll.h
index 28405a1d3b..d017158154 100644
--- a/src/systemd/sd-ipv4ll.h
+++ b/src/systemd/sd-ipv4ll.h
@@ -47,7 +47,8 @@ int sd_ipv4ll_set_address_seed(sd_ipv4ll *ll, uint8_t seed[8]);
 bool sd_ipv4ll_is_running(sd_ipv4ll *ll);
 int sd_ipv4ll_start(sd_ipv4ll *ll);
 int sd_ipv4ll_stop(sd_ipv4ll *ll);
-void sd_ipv4ll_free(sd_ipv4ll *ll);
-int sd_ipv4ll_new(sd_ipv4ll **ret);
+sd_ipv4ll *sd_ipv4ll_ref(sd_ipv4ll *ll);
+sd_ipv4ll *sd_ipv4ll_unref(sd_ipv4ll *ll);
+int sd_ipv4ll_new (sd_ipv4ll **ret);
 
 #endif