manager: fix race condition while enumerating devices at startupbg/link-rename-race-rhel25808

While enumerating devices at startup, we take a snapshot of existing
links from platform and we start creating device instances for
them. It's possible that in the meantime, while processing netlink
events in platform_link_added(), a link gets renamed. If that happens,
then we have two different views of the same ifindex: the cached link
from `links` and the link in platform.

This can cause issues: in platform_link_added() we create the device
with the cached name; then in NMDevice's constructor(), we look up
from platform the ifindex for the given name. Because of the rename,
this lookup can match a newly created, different link.

The end result is that the ifindex from the initial snapshot doesn't
get a NMDevice and is not handled by NetworkManager.

Fix this problem by fetching the latest version of the link from
platform to make sure we have a consistent view of the state.

https://issues.redhat.com/browse/RHEL-25808
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1897

1 files changed, 16 insertions, 1 deletions

diff --git a/src/core/nm-manager.c b/src/core/nm-manager.c
index f607569d88..c30a2ff632 100644
--- a/src/core/nm-manager.c
+++ b/src/core/nm-manager.c
@@ -4438,10 +4438,25 @@ platform_query_devices(NMManager *self)
     links        = nm_platform_link_get_all(priv->platform);
     if (!links)
         return;
+
     for (i = 0; i < links->len; i++) {
-        const NMPlatformLink          *link = NMP_OBJECT_CAST_LINK(links->pdata[i]);
+        const NMPlatformLink          *elem = NMP_OBJECT_CAST_LINK(links->pdata[i]);
+        const NMPlatformLink          *link;
         const NMConfigDeviceStateData *dev_state;
 
+        /*
+         * @links is an immutable snapshot of the platform links captured before
+         * the loop was started. It's possible that in the meantime, while
+         * processing netlink events in platform_link_added(), a link was
+         * renamed.  If that happens, we have 2 different views of the same
+         * ifindex: the one from @links and the one from platform. This can
+         * cause race conditions; make sure to use the latest known version of
+         * the link.
+         */
+        link = nm_platform_link_get(priv->platform, elem->ifindex);
+        if (!link)
+            continue;
+
         dev_state = nm_config_device_state_get(priv->config, link->ifindex);
         platform_link_added(self,
                             link->ifindex,