net/sched: fix error recovery in qdisc_create()

If TCA_STAB attribute is malformed, qdisc_get_stab() returns
an error, and we end up calling ops->destroy() while ops->init()
has not been called yet.

While we are at it, call qdisc_put_stab() after ops->destroy().

Fixes: 1f62879 ("net/sched: make stab available before ops->init() call")
Reported-by: syzbot+d44d88f1d11e6ca8576b@syzkaller.appspotmail.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Vladimir Oltean <vladimir.oltean@nxp.com>
Cc: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -1286,22 +1286,22 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 		stab = qdisc_get_stab(tca[TCA_STAB], extack);
 		if (IS_ERR(stab)) {
 			err = PTR_ERR(stab);
-			goto err_out4;
+			goto err_out3;
 		}
 		rcu_assign_pointer(sch->stab, stab);
 	}
 
 	if (ops->init) {
 		err = ops->init(sch, tca[TCA_OPTIONS], extack);
 		if (err != 0)
-			goto err_out5;
+			goto err_out4;
 	}
 
 	if (tca[TCA_RATE]) {
 		err = -EOPNOTSUPP;
 		if (sch->flags & TCQ_F_MQROOT) {
 			NL_SET_ERR_MSG(extack, "Cannot attach rate estimator to a multi-queue root qdisc");
-			goto err_out5;
+			goto err_out4;
 		}
 
 		err = gen_new_estimator(&sch->bstats,
@@ -1312,7 +1312,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 					tca[TCA_RATE]);
 		if (err) {
 			NL_SET_ERR_MSG(extack, "Failed to generate new estimator");
-			goto err_out5;
+			goto err_out4;
 		}
 	}
 
@@ -1321,12 +1321,13 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 
 	return sch;
 
-err_out5:
-	qdisc_put_stab(rtnl_dereference(sch->stab));
 err_out4:
-	/* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
+	/* Even if ops->init() failed, we call ops->destroy()
+	 * like qdisc_create_dflt().
+	 */
 	if (ops->destroy)
 		ops->destroy(sch);
+	qdisc_put_stab(rtnl_dereference(sch->stab));
 err_out3:
 	netdev_put(dev, &sch->dev_tracker);
 	qdisc_free(sch);