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From:   Paul Moore <paul@paul-moore.com>
Date:   Fri, 20 Jan 2023 13:58:53 -0500
Message-ID: <CAHC9VhTgesdmF3-+oP-EYuNZ-8LKXGPYuSffVst_Wca5Oj0EAQ@mail.gmail.com>
Subject: Re: [PATCH v6 3/3] fanotify,audit: Allow audit to use the full
 permission event response
To:     Richard Guy Briggs <rgb@redhat.com>
Cc:     Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
        Eric Paris <eparis@parisplace.org>,
        Steve Grubb <sgrubb@redhat.com>, Jan Kara <jack@suse.cz>,
        Amir Goldstein <amir73il@gmail.com>
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On Tue, Jan 17, 2023 at 4:14 PM Richard Guy Briggs <rgb@redhat.com> wrote:
>
> 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 <paul@paul-moore.com>.
>
> The {subj,obj}_trust values are {0,1,2}, corresponding to no, yes, unknown.
>
> 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 <sgrubb@redhat.com>
> Link: https://lore.kernel.org/r/3075502.aeNJFYEL58@x2
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
>  fs/notify/fanotify/fanotify.c |  3 ++-
>  include/linux/audit.h         |  9 +++++----
>  kernel/auditsc.c              | 16 +++++++++++++---
>  3 files changed, 20 insertions(+), 8 deletions(-)

...

> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index d1fb821de104..3133c4175c15 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -2877,10 +2878,19 @@ 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);
> +       /* {subj,obj}_trust values are {0,1,2}: no,yes,unknown */
> +       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);
> +               return;
> +       }
> +       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);
>  }

The only thing that comes to mind might be to convert the if-return
into a switch statement to make it a bit cleaner and easier to patch
in the future, but that is soooo far removed from any real concern
that I debated even mentioning it.  I only bring it up in case the
"3F" discussion results in a respin, and even then I'm not going to
hold my ACK over something as silly as a if-return vs switch.

For clarity, this is what I was thinking:

void __audit_fanontify(...)
{
  switch (type) {
  case FAN_RESPONSE_INFO_NONE:
    audit_log(...);
    break;
  default:
    audit_log(...);
  }
}

-- 
paul-moore.com