audit: Fix wrong task in comparison of session ID

The audit_filter_rules() function in auditsc.c compared the session ID
with the credentials of the current task, while it should use the
credentials of the task given to audit_filter_rules() as a parameter
(tsk).

GitHub issue:
https://github.com/linux-audit/audit-kernel/issues/82

Fixes: 8fae47705685 ("audit: add support for session ID user filter")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
[PM: not user visible, dropped stable]
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/auditsc.c

@@ -517,7 +517,7 @@ static int audit_filter_rules(struct task_struct *tsk,
 			result = audit_gid_comparator(cred->fsgid, f->op, f->gid);
 			break;
 		case AUDIT_SESSIONID:
-			sessionid = audit_get_sessionid(current);
+			sessionid = audit_get_sessionid(tsk);
 			result = audit_comparator(sessionid, f->op, f->val);
 			break;
 		case AUDIT_PERS: