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 32 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 v3: - 1/3 switch {,__}audit_fanotify() from uint to u32 - 2/3 re-add fanotify_get_response switch case FAN_DENY: to avoid unnecessary churn - add FAN_EXTRA flag to indicate more info and break with old kernel - change response from u16 to u32 to avoid endian issues - change extra_info_buf to union - move low-cost fd check earlier - change FAN_RESPONSE_INFO_AUDIT_NONE to FAN_RESPONSE_INFO_NONE - switch to u32 for internal and __u32 for uapi Link: https://lore.kernel.org/r/cover.1652724390.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 | 6 ++- fs/notify/fanotify/fanotify.h | 4 +- fs/notify/fanotify/fanotify_user.c | 76 +++++++++++++++++++----------- include/linux/audit.h | 9 ++-- include/linux/fanotify.h | 3 ++ include/uapi/linux/fanotify.h | 22 ++++++++- kernel/auditsc.c | 18 +++++-- 7 files changed, 100 insertions(+), 38 deletions(-) -- 2.27.0
