[PATCH ipsec-next v6 00/14] xfrm: XFRM_MSG_MIGRATE_STATE new netlink message

[Antony Antony <antony.antony@secunet.com>]

The current XFRM_MSG_MIGRATE interface is tightly coupled to policy and
SA migration, and it lacks the information required to reliably migrate
individual SAs. This makes it unsuitable for IKEv2 deployments,
dual-stack setups (IPv4/IPv6), and scenarios where policies are managed
externally (e.g., by daemons other than the IKE daemon).

Mandatory SA selector list
The current API requires a non-empty SA selector list, which does not
reflect the IKEv2 use case.
A single Child SA may correspond to multiple policies,
and SA discovery already occurs via address and reqid matching. With
dual-stack Child SAs this leads to excessive churn: the current method
would have to be called up to six times (in/out/fwd × v4/v6) on SA,
while the new method only requires two calls.

Selectors lack SPI (and marks)
XFRM_MSG_MIGRATE cannot uniquely identify an SA when multiple SAs share
the same policies (per-CPU SAs, SELinux label-based SAs, etc.). Without
the SPI, the kernel may update the wrong SA instance.

Reqid cannot be changed
Some implementations allocate reqids based on traffic selectors. In
host-to-host or selector-changing scenarios, the reqid must change,
which the current API cannot express.

Because strongSwan and other implementations manage policies
independently of the kernel, an interface that updates only a specific
SA - with complete and unambiguous identification - is required.

XFRM_MSG_MIGRATE_STATE provides that interface. It supports migration
of a single SA via xfrm_usersa_id (including SPI) and we fix
encap removal in this patch set, reqid updates, address changes,
and other SA-specific parameters. It avoids the structural limitations
of XFRM_MSG_MIGRATE and provides a simpler, extensible mechanism for
precise per-SA migration without involving policies.

New migration steps: first install block policy, remove the old policy,
call XFRM_MSG_MIGRATE_STATE for each state, then re-install the
policies and remove the block policy.

If the target SA tuple (daddr, SPI, proto, family) is already
occupied, the operation r/eturns -EEXIST. In this case the original
SA is not preserved. Userspace must handle -EEXIST by
re-establishing the SA at the IKE level and manage policies.

---
v5->v6: - add mark to look up SA.
	- restrict netlink attributes in new method
	- address review feedback from Sabrina
	- add new patch to fix existing inter-family address comparison
	- add extack xfrm_state_init()
	- Feedback from Yan : omit-to-inherit add migrating marks
	- Drop missing __rcu annotation on nlsk, Sabrina has a better patch

Link v5: https://lore.kernel.org/all/cover.1769509130.git.antony.antony@secunet.com/
v4->v5: add synchronize after migrate and delete it inside a lock
	- split xfrm_state_migrate into create and install functions
Link v4: https://lore.kernel.org/all/cover.1768811736.git.antony.antony@secunet.com/

v3->v4: add patch to fix pre-existing missing __rcu annotation on nlsk

v2->v3: - fix commit message formatting

v1->v2: dropped 6/6. That check is already there where the func is called
	- merged patch 4/6 and 5/6, to fix use uninitialized value
	- fix commit messages

---
Antony Antony (14):
      xfrm: remove redundant assignments
      xfrm: add extack to xfrm_init_state
      xfrm: allow migration from UDP encapsulated to non-encapsulated ESP
      xfrm: fix NAT-related field inheritance in SA migration
      xfrm: rename reqid in xfrm_migrate
      xfrm: split xfrm_state_migrate into create and install functions
      xfrm: check family before comparing addresses in migrate
      xfrm: add state synchronization after migration
      xfrm: add error messages to state migration
      xfrm: move encap and xuo into struct xfrm_migrate
      xfrm: refactor XFRMA_MTIMER_THRESH validation into a helper
      xfrm: add XFRM_MSG_MIGRATE_STATE for single SA migration
      xfrm: restrict netlink attributes for XFRM_MSG_MIGRATE_STATE
      xfrm: docs: add documentation for XFRM_MSG_MIGRATE_STATE

 Documentation/networking/xfrm/index.rst            |   1 +
 .../networking/xfrm/xfrm_migrate_state.rst         | 129 +++++++++
 include/net/xfrm.h                                 |  74 ++++-
 include/uapi/linux/xfrm.h                          |  13 +
 net/ipv4/ipcomp.c                                  |   2 +-
 net/ipv6/ipcomp6.c                                 |   2 +-
 net/key/af_key.c                                   |  12 +-
 net/xfrm/xfrm_device.c                             |   2 +-
 net/xfrm/xfrm_policy.c                             |  24 +-
 net/xfrm/xfrm_state.c                              | 128 +++++----
 net/xfrm/xfrm_user.c                               | 308 ++++++++++++++++++++-
 security/selinux/nlmsgtab.c                        |   3 +-
 12 files changed, 604 insertions(+), 94 deletions(-)
---
base-commit: be14d13625c9b070c33c423026b598ed65695225
change-id: migrate-state-063ee0342680

Best regards,
-- 
Antony Antony <<antony.antony@secunet.com>>