ima: Fix return value of ima_write_policy()

This patch fixes the return value of ima_write_policy() when a new policy
is directly passed to IMA and the current policy requires appraisal of the
file containing the policy. Currently, if appraisal is not in ENFORCE mode,
ima_write_policy() returns 0 and leads user space applications to an
endless loop. Fix this issue by denying the operation regardless of the
appraisal mode.

Cc: [e-mail] # 4.10.x
Fixes: 19f8a84713edc ("ima: measure and appraise the IMA policy itself")
Signed-off-by: Roberto Sassu <[e-mail]>
Reviewed-by: Krzysztof Struczynski <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>

security/integrity/ima/ima_fs.c

···
 		integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, NULL,
 				    "policy_update", "signed policy required",
 				    1, 0);
-		if (ima_appraise & IMA_APPRAISE_ENFORCE)
-			result = -EACCES;
+		result = -EACCES;
 	} else {
 		result = ima_parse_add_rule(data);
 	}