Re: [PATCH 1/2] integrity: Add errno field in audit message

[Mimi Zohar <zohar@linux.ibm.com>]

On Wed, 2020-06-10 at 17:03 -0700, Lakshmi Ramasubramanian wrote:
> Error code is not included in the audit messages logged by
> the integrity subsystem. Add a new field namely "errno" in
> the audit message and set the value to the error code passed
> to integrity_audit_msg() in the "result" parameter.
> 
> Sample audit message:
> 
> [    6.284329] audit: type=1804 audit(1591756723.627:2): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=kernel op=add_boot_aggregate cause=alloc_entry errno=-12 comm="swapper/0" name="boot_aggregate" res=0
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> Suggested-by: Steve Grubb <sgrubb@redhat.com>
---
>  security/integrity/integrity_audit.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/integrity_audit.c b/security/integrity/integrity_audit.c
> index 5109173839cc..8cbf415bb977 100644
> --- a/security/integrity/integrity_audit.c
> +++ b/security/integrity/integrity_audit.c
> @@ -42,7 +42,8 @@ void integrity_audit_msg(int audit_msgno, struct inode *inode,
>  			 from_kuid(&init_user_ns, audit_get_loginuid(current)),
>  			 audit_get_sessionid(current));
>  	audit_log_task_context(ab);
> -	audit_log_format(ab, " op=%s cause=%s comm=", op, cause);
> +	audit_log_format(ab, " op=%s cause=%s errno=%d comm=",
> +			 op, cause, result);

The idea is a good idea, but you're assuming that "result" is always
errno.  That was probably true originally, but isn't now.  For
example, ima_appraise_measurement() calls xattr_verify(), which
compares the security.ima hash with the calculated file hash.  On
failure, it returns the result of memcmp().  Each and every code path
will need to be checked.

>  	audit_log_untrustedstring(ab, get_task_comm(name, current));
>  	if (fname) {
>  		audit_log_format(ab, " name=");