Re: [PATCH v5 3/3] fanotify,audit: Allow audit to use the full permission event response

On 2022-12-20 18:31, Paul Moore wrote:

On Mon, Dec 12, 2022 at 9:06 AM Richard Guy Briggs [off-list ref] wrote:

quoted

This patch passes the full response so that the audit function can use all
of it. The audit function was updated to log the additional information in
the AUDIT_FANOTIFY record.

Currently the only type of fanotify info that is defined is an audit
rule number, but convert it to hex encoding to future-proof the field.
Hex encoding suggested by Paul Moore [off-list ref].

Sample records:
  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=3F subj_trust=2 obj_trust=2

Suggested-by: Steve Grubb <redacted>
Link: https://lore.kernel.org/r/3075502.aeNJFYEL58@x2 (local)
Signed-off-by: Richard Guy Briggs <redacted>
---
 fs/notify/fanotify/fanotify.c |  3 ++-
 include/linux/audit.h         |  9 +++++----
 kernel/auditsc.c              | 25 ++++++++++++++++++++++---
 3 files changed, 29 insertions(+), 8 deletions(-)

...

quoted

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index d1fb821de104..8d523066d81f 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c

@@ -64,6 +64,7 @@
 #include <uapi/linux/limits.h>
 #include <uapi/linux/netfilter/nf_tables.h>
 #include <uapi/linux/openat2.h> // struct open_how
+#include <uapi/linux/fanotify.h>

 #include "audit.h"

@@ -2877,10 +2878,28 @@ void __audit_log_kern_module(char *name)
        context->type = AUDIT_KERN_MODULE;
 }

-void __audit_fanotify(u32 response)
+void __audit_fanotify(u32 response, struct fanotify_response_info_audit_rule *friar)
 {
-       audit_log(audit_context(), GFP_KERNEL,
-               AUDIT_FANOTIFY, "resp=%u", response);
+       struct audit_context *ctx = audit_context();
+       struct audit_buffer *ab;
+       char numbuf[12];
+
+       if (friar->hdr.type == FAN_RESPONSE_INFO_NONE) {
+               audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
+                         "resp=%u fan_type=%u fan_info=3F subj_trust=2 obj_trust=2",
+                         response, FAN_RESPONSE_INFO_NONE);

The fan_info, subj_trust, and obj_trust constant values used here are
awfully magic-numbery and not the usual sentinel values one might
expect for a "none" operation, e.g. zeros/INT_MAX/etc. I believe a
comment here explaining the values would be a good idea.

Ack.  I'll add a comment.  I would have preferred zero for default of
unset, but Steve requested 0/1/2 no/yes/unknown.

quoted

+               return;
+       }
+       ab = audit_log_start(ctx, GFP_KERNEL, AUDIT_FANOTIFY);
+       if (ab) {
+               audit_log_format(ab, "resp=%u fan_type=%u fan_info=",
+                                response, friar->hdr.type);
+               snprintf(numbuf, sizeof(numbuf), "%u", friar->rule_number);
+               audit_log_n_hex(ab, numbuf, sizeof(numbuf));

It looks like the kernel's printf format string parsing supports %X so
why not just use that for now, we can always complicate it later if
needed.  It would probably also remove the need for the @ab, @numbuf,
and @ctx variables.  For example:

audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
  "resp=%u fan_type=%u fan_info=%X subj_trust=%u obj_trust=%u",
  response, friar->hdr.type, friar->rule_number,
  friar->subj_trust, friar->obj_trust);

Am I missing something?

No, I am.  Thank you, that's much cleaner.

quoted

+               audit_log_format(ab, " subj_trust=%u obj_trust=%u",
+                                friar->subj_trust, friar->obj_trust);
+               audit_log_end(ab);
+       }
 }

 void __audit_tk_injoffset(struct timespec64 offset)
--
2.27.0

-- 
paul-moore.com

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- RGB

--
Richard Guy Briggs [off-list ref]
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
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