network: fix race between RTM_NEWLINK and NL82011_CMD_NEW_INTERFACE

When a new wireless network interface is created by the kernel, it emits
both RTM_NEWLINK and NL80211_CMD_NEW_INTERFACE. These events can arrive
in either order and networkd must behave correctly in both cases.

The typical case is that RTM_NEWLINK is handled first, in which case
networkd creates a Link object and starts tracking it. When the
NL80211_CMD_NEW_INTERFACE message is handled, networkd then populates
the Link object with relevant wireless properties such as wireless
interface type (managed, AP, etc.).

In the event that the order is reversed however, networkd will fail to
populate these wireless properties because at the time of processing the
nl80211 message, the link is considered unknown. In that case, a debug
message is emitted:

  systemd-networkd[467]: nl80211: received new_interface(7) message for link '109' we don't know about, ignoring.

This is problematic because after the subsequent RTM_NEWLINK message,
networkd will have an incomplete view of the link. In particular, if a
.network configuration matches on some of the missing wireless
properties, such as WLANInterfaceType=, then it will never match.

The above race can be reproduced by using the mac80211_hwsim driver.
Suppose that there exists a .network configuration:

  [Match]
  WLANInterfaceType=ap
  ...

Now loop the creation/destruction of such an AP interface:

  while true
  do
    iw dev wlan0 interface add uap0 type __ap
    iw dev uap0 del
  done

The above debug message from networkd will then be observed very
quickly. And in that event, the .network file will fail to match.

To address the above race, have the nl80211 message handler store the
interface index in a set in case a Link object is not found on
NL80211_CMD_NEW_INTERFACE. The handler for RTM_NEWLINK can then query
this set, and explicitly request the wireless properties from nl80211
upon the creation of the Link object.

diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index 95a7d75e53c4777b906870ba52dd88de4b2e1377..e43c04567a4a390ee27e57164ebb4cfa7ffdf446 100644 (file)
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -2515,6 +2515,15 @@ static int link_new(Manager *manager, sd_netlink_message *message, Link **ret) {
         log_link_debug(link, "Saved new link: ifindex=%i, iftype=%s(%u), kind=%s",
                        link->ifindex, strna(arphrd_to_name(link->iftype)), link->iftype, strna(link->kind));
 
+        /* If contained in this set, the link is wireless and the corresponding NL80211_CMD_NEW_INTERFACE
+         * message arrived too early. Request the wireless link information again.
+         */
+        if (set_remove(manager->new_wlan_ifindices, INT_TO_PTR(link->ifindex))) {
+                r = link_get_wlan_interface(link);
+                if (r < 0)
+                        log_link_warning_errno(link, r, "Failed to get wireless interface, ignoring: %m");
+        }
+
         *ret = TAKE_PTR(link);
         return 0;
 }

diff --git a/src/network/networkd-manager.c b/src/network/networkd-manager.c
index f82117cc1e6f8d525e545f0dd1746be742f97e09..ad668215e7bb09df1f5271f2ce78cd79e321f1bb 100644 (file)
--- a/src/network/networkd-manager.c
+++ b/src/network/networkd-manager.c
@@ -614,6 +614,7 @@ Manager* manager_free(Manager *m) {
         m->request_queue = ordered_set_free(m->request_queue);
 
         m->dirty_links = set_free_with_destructor(m->dirty_links, link_unref);
+        m->new_wlan_ifindices = set_free(m->new_wlan_ifindices);
         m->links_by_name = hashmap_free(m->links_by_name);
         m->links_by_hw_addr = hashmap_free(m->links_by_hw_addr);
         m->links_by_dhcp_pd_subnet_prefix = hashmap_free(m->links_by_dhcp_pd_subnet_prefix);

diff --git a/src/network/networkd-manager.h b/src/network/networkd-manager.h
index e6183af0e4ba3899bc7487a59391698aa2941420..c9cbcf928994d5b3090be8aa930f76e1cd1289aa 100644 (file)
--- a/src/network/networkd-manager.h
+++ b/src/network/networkd-manager.h
@@ -38,6 +38,7 @@ struct Manager {
         bool manage_foreign_rules;
 
         Set *dirty_links;
+        Set *new_wlan_ifindices;
 
         char *state_file;
         LinkOperationalState operational_state;

diff --git a/src/network/networkd-wifi.c b/src/network/networkd-wifi.c
index e35857261e07a01b7b38a1579dca799867ca8df7..1a3754b29ce1b85b34655113ebfacaa53f1c2a8a 100644 (file)
--- a/src/network/networkd-wifi.c
+++ b/src/network/networkd-wifi.c
@@ -92,6 +92,19 @@ int manager_genl_process_nl80211_config(sd_netlink *genl, sd_netlink_message *me
         if (r < 0) {
                 log_debug_errno(r, "nl80211: received %s(%u) message for link '%"PRIu32"' we don't know about, ignoring.",
                                 strna(nl80211_cmd_to_string(cmd)), cmd, ifindex);
+
+                /* The NL80211_CMD_NEW_INTERFACE message might arrive before RTM_NEWLINK, in which case a
+                 * link will not have been created yet. Store the interface index such that the wireless
+                 * properties of the link (such as wireless interface type) are queried again after the link
+                 * is created.
+                 */
+                if (cmd == NL80211_CMD_NEW_INTERFACE) {
+                        r = set_ensure_put(&manager->new_wlan_ifindices, NULL, INT_TO_PTR(ifindex));
+                        if (r < 0)
+                                log_warning_errno(r, "Failed to add new wireless interface index to set, ignoring: %m");
+                } else if (cmd == NL80211_CMD_DEL_INTERFACE)
+                        set_remove(manager->new_wlan_ifindices, INT_TO_PTR(ifindex));
+
                 return 0;
         }