Merge branch 'so_passrights'

Kuniyuki Iwashima says:
====================

af_unix: Introduce SO_PASSRIGHTS.

As long as recvmsg() or recvmmsg() is used with cmsg, it is not
possible to avoid receiving file descriptors via SCM_RIGHTS.

This series introduces a new socket option, SO_PASSRIGHTS, to allow
disabling SCM_RIGHTS.  The option is enabled by default.

See patch 8 for background/context.

This series is related to [0], but is split into a separate series,
as most of the patches are specific to af_unix.

The v2 of the BPF LSM extension part will be posted later, once
this series is merged into net-next and has landed in bpf-next.

[0]: https://lore.kernel.org/bpf/20250505215802.48449-1-kuniyu@amazon.com/

Changes:
  v5:
    * Patch 4
      * Fix BPF selftest failure (setget_sockopt.c)

  v4: https://lore.kernel.org/netdev/20250515224946.6931-1-kuniyu@amazon.com/
    * Patch 6
      * Group sk->sk_scm_XXX bits by struct
    * Patch 9
      * Remove errno handling

  v3: https://lore.kernel.org/netdev/20250514165226.40410-1-kuniyu@amazon.com/
    * Patch 3
      * Remove inline in scm.c
    * Patch 4 & 5 & 8
      * Return -EOPNOTSUPP in getsockopt()
    * Patch 5
      * Add CONFIG_SECURITY_NETWORK check for SO_PASSSEC
    * Patch 6
      * Add kdoc for sk_scm_unused
      * Update sk_scm_XXX under lock_sock() in setsockopt()
    * Patch 7
      * Update changelog (recent change -> aed6ecef55d7)

  v2: https://lore.kernel.org/netdev/20250510015652.9931-1-kuniyu@amazon.com/
    * Added patch 4 & 5 to reuse sk_txrehash for scm_recv() flags

  v1: https://lore.kernel.org/netdev/20250508013021.79654-1-kuniyu@amazon.com/
====================

Signed-off-by: David S. Miller <davem@davemloft.net>