network: ignore stale interface renames

After enumeration, networkd may receive RTM_NEWLINK messages carrying a
stale interface name. This can happen when interface rename notifications
are queued before link enumeration and processed afterwards.

Previously, networkd could become confused by such a message and put the
corresponding Link into the failed state. Avoid this by checking whether
the new interface name is already in use by another interface and ignoring
the rename if so.

Fixes #20203.

diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index 20db5fa73a78baa506b384a05931680252751fd2..f505031e1e1b7c6fec2664d4eb2d5db8fe7abce8 100644 (file)
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -2593,6 +2593,19 @@ static int link_update_alternative_names(Link *link, sd_netlink_message *message
         if (strv_equal(altnames, link->alternative_names))
                 return 0;
 
+        /* See the comment in link_update_name(). If one of the new alternative names is already in use by
+         * another interface, the alternative-name information in this message is likely stale. Ignore the
+         * entire IFLA_ALT_IFNAME attribute in that case. */
+        STRV_FOREACH(n, altnames) {
+                Link *existing;
+                if (link_get_by_name(link->manager, *n, &existing) >= 0 && existing != link) {
+                        log_link_debug(link,
+                                       "Alternative interface name update detected, but the new name '%s' is already in use by another interface (ifindex=%i), ignoring the update as it may be stale.",
+                                       *n, existing->ifindex);
+                        return 0;
+                }
+        }
+
         STRV_FOREACH(n, link->alternative_names)
                 hashmap_remove_value(link->manager->links_by_name, *n, link);
 
@@ -2624,6 +2637,47 @@ static int link_update_name(Link *link, sd_netlink_message *message) {
         if (streq(ifname, link->ifname))
                 return 0;
 
+        /* Check if the new interface name is already used by another interface. If so, the rename is likely
+         * stale. Consider the following race:
+         *
+         * 1. networkd enables rtnl matches in manager_connect_rtnl().
+         * 2. The kernel sends an RTM_NEWLINK notification for an interface (say, ifindex=2, ifname="eth0"),
+         *    and the notification message (A) is queued in networkd's sd-netlink object.
+         * 3. The interface is renamed (say, "eth0" -> "enp0"), e.g. by udevd. The kernel sends another
+         *    RTM_NEWLINK notification for the rename, and the notification message (B) is also queued in
+         *    networkd's sd-netlink object.
+         * 4. The kernel detects another new interface (say, ifindex=3). Since the name "eth0" is now unused,
+         *    the interface is named "eth0".
+         * 5. networkd enumerates links and creates Link objects for:
+         *    - ifindex=2, ifname="enp0"
+         *    - ifindex=3, ifname="eth0"
+         * 6. After enumeration, when processing message (A), networkd becomes confused and thinks that the
+         *    interface with ifindex=2 was renamed from "enp0" to "eth0". However, it fails to update the
+         *    Manager.links_by_name hashmap because "eth0" is already used by the interface with ifindex=3.
+         * 7. When processing message (B), networkd thinks that the interface with ifindex=2 has been renamed
+         *    again from "eth0" to "enp0", and renames the Link object back to "enp0".
+         *
+         * When this happens, we get something like the following:
+         *
+         * systemd-networkd[5164]: enp0: Interface name change detected, renamed to eth0.
+         * systemd-networkd[5164]: eth0: Failed to manage link by its new name: File exists
+         * systemd-networkd[5164]: Could not process link message: File exists
+         * systemd-networkd[5164]: eth0: Failed
+         * systemd-networkd[5164]: eth0: State changed: initialized -> failed
+         * systemd-networkd[5164]: eth0: Interface name change detected, renamed to enp0.
+         *
+         * See also #20203.
+         *
+         * To avoid the race, ignore the rename. A subsequent RTM_NEWLINK message should eventually provide
+         * the current interface name, e.g. message (B) above. */
+        Link *existing;
+        if (link_get_by_name(link->manager, ifname, &existing) >= 0 && existing != link) {
+                log_link_debug(link,
+                               "Interface name change detected, but the new interface name '%s' is already in use by another interface (ifindex=%i), ignoring the rename as it may be stale.",
+                               ifname, existing->ifindex);
+                return 0;
+        }
+
         log_link_info(link, "Interface name change detected, renamed to %s.", ifname);
 
         hashmap_remove_value(link->manager->links_by_name, link->ifname, link);