apparmor: Fix use-after-free in aa_audit_rule_init

In the implementation of aa_audit_rule_init(), when aa_label_parse()
fails the allocated memory for rule is released using
aa_audit_rule_free(). But after this release, the return statement
tries to access the label field of the rule which results in
use-after-free. Before releasing the rule, copy errNo and return it
after release.

Fixes: 52e8c380 ("apparmor: Fix memory leak of rule on error exit path")
Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/audit.c

@@ -197,8 +197,9 @@ int aa_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
 	rule->label = aa_label_parse(&root_ns->unconfined->label, rulestr,
 				     GFP_KERNEL, true, false);
 	if (IS_ERR(rule->label)) {
+		int err = PTR_ERR(rule->label);
 		aa_audit_rule_free(rule);
-		return PTR_ERR(rule->label);
+		return err;
 	}
 
 	*vrule = rule;