netdev - Some sort of netlink RTM_GET(ROUTE|RULE|NEIGH) regression(?) in 6.10-rc3 vs 6.9

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Date: Thu, 13 Jun 2024 14:18:41 +0200
From: Maciej Żenczykowski <maze@...gle.com>
To: Linux NetDev <netdev@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>
Subject: Some sort of netlink RTM_GET(ROUTE|RULE|NEIGH) regression(?) in
 6.10-rc3 vs 6.9

The Android net tests
(available at https://cs.android.com/android/platform/superproject/main/+/main:kernel/tests/net/test/
more specifically multinetwork_test.py & neighbour_test.py)
run via:
  /...aosp-tests.../net/test/run_net_test.sh --builder
from within a 6.10-rc3 kernel tree are falling over due to a *plethora* of:
  TypeError: NLMsgHdr requires a bytes object of length 16, got 4

The problems might be limited to RTM_GETROUTE and RTM_GETRULE and RTM_GETNEIGH,
as various other netlink using xfrm tests appear to be okay...

(note: 6.10-rc3 also fails to build for UML due to a buggy bpf change,
but I sent out a 1-line fix for that already:
https://patchwork.kernel.org/project/netdevbpf/patch/20240613112520.1526350-1-maze@google.com/
)

It is of course entirely possible the test code is buggy in how it
parses netlink, but it has worked for years and years...

Before I go trying to bisect this... anyone have any idea what might
be the cause?
Perhaps some sort of change to how these dumps work? Some sort of new
netlink extended errors?

- Maciej