[RFC,0/2] keys: request_key() interception in containers

Message

David Howells Feb. 4, 2021, 5:47 p.m. UTC

Here's a rough draft of a facility by which keys can be intercepted.

There are two patches:

 (1) Add tags to namespaces that can be used to find out, when we're
     looking for an intercept, if a namespace that an intercept is
     filtering on is the same as namespace of the caller of request_key()
     without the need for the intercept record to pin the namespaces that
     it's using as filters (which would also cause a dependency cycle).

     Tags contain only a refcount and are compared by address.

 (2) Add a new keyctl:

            keyctl(KEYCTL_SERVICE_INTERCEPT,
                   int queue_keyring, int userns_fd,
                   const char *type_name, unsigned int ns_mask);

     that allows a request_key() intercept to be added to the specified
     user namespace.  The authorisation key for an intercepted request is
     placed in the queue_keyring, which can be watched to gain a
     notification of this happening.  The watcher can then examine the auth
     key to determine what key is to be instantiated.

     A simple sample is provided that can be used to try this.

Some things that need to be worked out:

 (*) Intercepts are linked to the lifetime of the user_namespace on which
     they're placed, but not the daemon or the queue keyring.  Probably
     they should be removed when the queue keyring is removed, but they
     currently pin it.

 (*) Setting userns_fd to other than -1 is not yet supported (-1 indicates
     the current user namespace).

 (*) Multiple threads can monitor a queue keyring, but they will all get
     woken.  They can use keyctl_move() to decide who gets to process it.


The patches can be found on the following branch:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=keys-intercept

David
---
David Howells (2):
      Add namespace tags that can be used for matching without pinning a ns
      keys: Allow request_key upcalls from a container to be intercepted


 include/linux/key-type.h                |   4 +-
 include/linux/user_namespace.h          |   2 +
 include/uapi/linux/keyctl.h             |  13 +
 kernel/user.c                           |   3 +
 kernel/user_namespace.c                 |   2 +
 samples/watch_queue/Makefile            |   2 +
 samples/watch_queue/key_req_intercept.c | 271 +++++++++++++++++++
 security/keys/Makefile                  |   2 +
 security/keys/compat.c                  |   3 +
 security/keys/internal.h                |   5 +
 security/keys/keyctl.c                  |   6 +
 security/keys/keyring.c                 |   1 +
 security/keys/process_keys.c            |   2 +-
 security/keys/request_key.c             |  16 +-
 security/keys/request_key_auth.c        |   3 +
 security/keys/service.c                 | 337 ++++++++++++++++++++++++
 16 files changed, 663 insertions(+), 9 deletions(-)
 create mode 100644 samples/watch_queue/key_req_intercept.c
 create mode 100644 security/keys/service.c