[PATCH ipsec-next v5 0/8] 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 returns -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.

Antony Antony (8):
  xfrm: add missing __rcu annotation to nlsk
  xfrm: remove redundant assignments
  xfrm: allow migration from UDP encapsulated to non-encapsulated ESP
  xfrm: rename reqid in xfrm_migrate
  xfrm: split xfrm_state_migrate into create and install functions
  xfrm: add state synchronization after migration
  xfrm: add error messages to state migration
  xfrm: add XFRM_MSG_MIGRATE_STATE for single SA migration

 include/net/netns/xfrm.h    |   2 +-
 include/net/xfrm.h          |  60 ++++++++++--
 include/uapi/linux/xfrm.h   |  11 +++
 net/key/af_key.c            |  10 +-
 net/xfrm/xfrm_policy.c      |   5 +-
 net/xfrm/xfrm_state.c       | 119 +++++++++++++++---------
 net/xfrm/xfrm_user.c        | 180 +++++++++++++++++++++++++++++++++++-
 security/selinux/nlmsgtab.c |   3 +-
 8 files changed, 324 insertions(+), 66 deletions(-)
---
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

v2->v3: - fix commit message formatting

v3->v4: add patch to fix pre-existing missing __rcu annotation on nlsk
   (exposed by sparse when modifying xfrm_user.c)
v4->v5: add synchronize after migrate and delete it inside a lock
    - split xfrm_state_migrate into create and install functions

-antony