[PATCH v4 4/4] fanotify, audit: deliver fan_info as a hex-encoded string

[Steve Grubb]

Hello Richard,

Although I have it working, I have some comments below that might improve
things.

On Tuesday, August 9, 2022 1:22:55 PM EDT Richard Guy Briggs wrote:
> 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.
> 
> Sample record:
>   type=FANOTIFY msg=audit(1659730979.839:284): resp=1 fan_type=0
> fan_info=3F
> 
> Suggested-by: Paul Moore <paul at paul-moore.com>
> Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
> ---
>  kernel/auditsc.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index f000fec52360..0f747015c577 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -2908,22 +2908,36 @@ void __audit_fanotify(u32 response, size_t len,
> char *buf)
> 
>  	if (!(len && buf)) {
>  		audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
> -			  "resp=%u fan_type=0 fan_info=?", response);
> +			  "resp=%u fan_type=0 fan_info=3F", response); /* "?" */
>  		return;
>  	}
>  	while (c >= sizeof(struct fanotify_response_info_header)) {
> +		struct audit_context *ctx = audit_context();
> +		struct audit_buffer *ab;
> +
>  		friar = (struct fanotify_response_info_audit_rule *)buf;
>  		switch (friar->hdr.type) {
>  		case FAN_RESPONSE_INFO_AUDIT_RULE:
>  			if (friar->hdr.len < sizeof(*friar)) {
> -				audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
> -					  "resp=%u fan_type=%u fan_info=(incomplete)",
> -					  response, friar->hdr.type);
> +				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);
> +#define INCOMPLETE "(incomplete)"
> +					audit_log_n_hex(ab, INCOMPLETE, sizeof(INCOMPLETE));
> +					audit_log_end(ab);
> +				}
>  				return;
>  			}
> -			audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
> -				  "resp=%u fan_type=%u fan_info=%u",
> -				  response, friar->hdr.type, friar->audit_rule);
> +			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);
> +				audit_log_n_hex(ab, (char *)&friar->audit_rule,
> +						sizeof(friar->audit_rule));

One thing to point out, the structure has a member audit_rule. It is
probably better to call it rule_number. This is because it has nothing to
do with any actual audit rule. It is a rule number meant to be recorded by
the audit system.

Also, that member is a __u32 type. Hex encoding that directly gives back a
__u32 when decoded - which is a bit unexpected since everything else is
strings. It would be better to convert the u32 to a base 10 string and then
hex encode that. A buffer of 12 bytes should be sufficient.

Thanks,
-Steve

> +				audit_log_end(ab);
> +
> +			}
>  		}
>  		c -= friar->hdr.len;
>  		ib += friar->hdr.len;