Hello Richard, On Friday, February 3, 2023 4:35:13 PM EST Richard Guy Briggs wrote: > 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 patchset defines a new flag (FAN_INFO) and new extensions that > define additional information which are appended after the response > structure returned from user space on a permission event. The appended > information is organized with headers containing a type and size that > can be delegated to interested subsystems. One new information type is > defined to audit the triggering rule number. > > A newer kernel will work with an older userspace and an older kernel > will behave as expected and reject a newer userspace, leaving it up to > the newer userspace to test appropriately and adapt as necessary. This > is done by providing a a fully-formed FAN_INFO extension but setting the > fd to FAN_NOFD. On a capable kernel, it will succeed but issue no audit > record, whereas on an older kernel it will fail. I have taken the patches and built a new kernel. Everything looks good to me on the audit side. It's acting as expected. You can put me down for an ACK or tested-by or whatever is appropriate. -Steve > The audit function was updated to log the additional information in the > AUDIT_FANOTIFY record. The following are examples of the new record > format: > type=FANOTIFY msg=audit(1600385147.372:590): resp=2 fan_type=1 > fan_info=3137 subj_trust=3 obj_trust=5 type=FANOTIFY > msg=audit(1659730979.839:284): resp=1 fan_type=0 fan_info=0 subj_trust=2 > obj_trust=2 > > 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/all/cover.1652730821.git.rgb@xxxxxxxxxx > > v4: > - scrap FAN_INVALID_RESPONSE_MASK in favour of original to catch invalid > response == 0 - introduce FANOTIFY_RESPONSE_* macros > - uapi: remove union > - keep original struct fanotify_response, add fan_info infra starting with > audit reason - uapi add struct fanotify_response_info_header{type/pad/len} > and struct fanotify_response_info_audit_rule{hdr/rule} - rename fan_ctx= > to fan_info=, FAN_EXTRA to FAN_INFO > - change event struct from type/buf to len/buf > - enable multiple info extensions in one message > - hex encode fan_info in __audit_fanotify() > - record type FANOTIFY extended to "type=FANOTIFY > msg=audit(1659730979.839:284): resp=1 fan_type=0 fan_info=3F" Link: > https://lore.kernel.org/all/cover.1659996830.git.rgb@xxxxxxxxxx > > v5: > - fixed warnings in p2/4 and p3/4 found by <lkp@xxxxxxxxx> > - restore original behaviour for !FAN_INFO case and fanotify_get_response() > - rename member audit_rule to rule_number > - eliminate memory leak of info_buf on failure (no longer dynamic) > - rename buf:info, count:info_len, c:remain, ib:infop > - fix pr_debug > - return -ENOENT on FAN_INFO and fd==FAN_NOFD to signal new kernel > - fanotify_write() remove redundant size check > - add u32 subj_trust obj_trust fields with unknown value "2" > - split out to helper process_access_response_info() > - restore finish_permission_event() response_struct to u32 > - assume and enforce one rule to audit, pass struct directly to > __audit_fanotify() - change fanotify_perm_event struct to union > hdr/audir_rule > - add vspace to fanotify_write() and process_access_response_info() > - squash 3/4 with 4/4 > - fix v3 and v4 links > Link: https://lore.kernel.org/all/cover.1670606054.git.rgb@xxxxxxxxxx > > v6: > - simplify __audit_fanotify() from audit_log_format/audit_log_n_hex to > audit_log/%X - add comment to clarify {subj,obj}_trust values > - remove fd processing from process_access_response_info() > - return info_len immediately from process_access_response() on FAN_NOFD > after process_access_response_info() Link: > https://lore.kernel.org/all/cover.1673989212.git.rgb@xxxxxxxxxx > > v7: > - change non FAN_INFO case to "0" > - change from if-return to switch(type)-case, which now ignores non-audit > info Link: https://lore.kernel.org/all/cover.1675373475.git.rgb@xxxxxxxxxx > > Richard Guy Briggs (3): > fanotify: Ensure consistent variable type for response > fanotify: define struct members to hold response decision context > fanotify,audit: Allow audit to use the full permission event response > > fs/notify/fanotify/fanotify.c | 8 ++- > fs/notify/fanotify/fanotify.h | 6 +- > fs/notify/fanotify/fanotify_user.c | 88 ++++++++++++++++++++++-------- > include/linux/audit.h | 9 +-- > include/linux/fanotify.h | 5 ++ > include/uapi/linux/fanotify.h | 30 +++++++++- > kernel/auditsc.c | 18 +++++- > 7 files changed, 131 insertions(+), 33 deletions(-)
