[PATCH v2 0/3] fanotify: Allow user space to pass back additional audit info

[Richard Guy Briggs]

The Fanotify API can be used for access control by requesting permission
event notification. The user space tooling that uses it may have a
complicated policy that inherently contains additional context for the
decision. If this information were available in the audit trail, policy
writers can close the loop on debugging policy. Also, if this additional
information were available, it would enable the creation of tools that
can suggest changes to the policy similar to how audit2allow can help
refine labeled security.

This patch defines 2 additional fields within the response structure
returned from user space on a permission event. The first field is 16
bits for the context type. The context type will describe what the
meaning is of the second field. The audit system will separate the
pieces and log them individually.

The audit function was updated to log the additional information in the
AUDIT_FANOTIFY record. The following is an example of the new record
format:

type=FANOTIFY msg=audit(1600385147.372:590): resp=2 fan_type=1 fan_ctx=17

changelog:
v1:
- first version by Steve Grubb <sgrubb@xxxxxxxxxx>
Link: https://lore.kernel.org/r/2042449.irdbgypaU6@x2

v2:
- enhancements suggested by Jan Kara <jack@xxxxxxx>
- 1/3 change %d to %u in pr_debug
- 2/3 change response from __u32 to __u16
- mod struct fanotify_response and fanotify_perm_event add extra_info_type, extra_info_buf
- extra_info_buf size max FANOTIFY_MAX_RESPONSE_EXTRA_LEN, add struct fanotify_response_audit_rule
- extend debug statements
- remove unneeded macros
- [internal] change interface to finish_permission_event() and process_access_response()
- 3/3 update format of extra information
- [internal] change interface to audit_fanotify()
- change ctx_type= to fan_type=
Link: https://lore.kernel.org/r/cover.1651174324.git.rgb@xxxxxxxxxx

Richard Guy Briggs (3):
  fanotify: Ensure consistent variable type for response
  fanotify: define struct members to hold response decision context
  fanotify: Allow audit to use the full permission event response

 fs/notify/fanotify/fanotify.c      |  5 ++-
 fs/notify/fanotify/fanotify.h      |  4 +-
 fs/notify/fanotify/fanotify_user.c | 59 ++++++++++++++++++++----------
 include/linux/audit.h              |  8 ++--
 include/linux/fanotify.h           |  3 ++
 include/uapi/linux/fanotify.h      | 27 +++++++++++++-
 kernel/auditsc.c                   | 18 +++++++--
 7 files changed, 94 insertions(+), 30 deletions(-)

-- 
2.27.0