[NET_SCHED]: Fix fallout from dev->qdisc RCU change

The move of qdisc destruction to a rcu callback broke locking in the
entire qdisc layer by invalidating previously valid assumptions about
the context in which changes to the qdisc tree occur.

The two assumptions were:

- since changes only happen in process context, read_lock doesn't need
  bottem half protection. Now invalid since destruction of inner qdiscs,
  classifiers, actions and estimators happens in the RCU callback unless
  they're manually deleted, resulting in dead-locks when read_lock in
  process context is interrupted by write_lock_bh in bottem half context.

- since changes only happen under the RTNL, no additional locking is
  necessary for data not used during packet processing (f.e. u32_list).
  Again, since destruction now happens in the RCU callback, this assumption
  is not valid anymore, causing races while using this data, which can
  result in corruption or use-after-free.

Instead of "fixing" this by disabling bottem halfs everywhere and adding
new locks/refcounting, this patch makes these assumptions valid again by
moving destruction back to process context. Since only the dev->qdisc
pointer is protected by RCU, but ->enqueue and the qdisc tree are still
protected by dev->qdisc_lock, destruction of the tree can be performed
immediately and only the final free needs to happen in the rcu callback
to make sure dev_queue_xmit doesn't access already freed memory.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 8 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index a19eff1..0b64892 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -195,14 +195,14 @@ struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle)
 {
 	struct Qdisc *q;
 
-	read_lock_bh(&qdisc_tree_lock);
+	read_lock(&qdisc_tree_lock);
 	list_for_each_entry(q, &dev->qdisc_list, list) {
 		if (q->handle == handle) {
-			read_unlock_bh(&qdisc_tree_lock);
+			read_unlock(&qdisc_tree_lock);
 			return q;
 		}
 	}
-	read_unlock_bh(&qdisc_tree_lock);
+	read_unlock(&qdisc_tree_lock);
 	return NULL;
 }
 
@@ -837,7 +837,7 @@ static int tc_dump_qdisc(struct sk_buff *skb, struct netlink_callback *cb)
 			continue;
 		if (idx > s_idx)
 			s_q_idx = 0;
-		read_lock_bh(&qdisc_tree_lock);
+		read_lock(&qdisc_tree_lock);
 		q_idx = 0;
 		list_for_each_entry(q, &dev->qdisc_list, list) {
 			if (q_idx < s_q_idx) {
@@ -846,12 +846,12 @@ static int tc_dump_qdisc(struct sk_buff *skb, struct netlink_callback *cb)
 			}
 			if (tc_fill_qdisc(skb, q, q->parent, NETLINK_CB(cb->skb).pid,
 					  cb->nlh->nlmsg_seq, NLM_F_MULTI, RTM_NEWQDISC) <= 0) {
-				read_unlock_bh(&qdisc_tree_lock);
+				read_unlock(&qdisc_tree_lock);
 				goto done;
 			}
 			q_idx++;
 		}
-		read_unlock_bh(&qdisc_tree_lock);
+		read_unlock(&qdisc_tree_lock);
 	}
 
 done:
@@ -1074,7 +1074,7 @@ static int tc_dump_tclass(struct sk_buff *skb, struct netlink_callback *cb)
 	s_t = cb->args[0];
 	t = 0;
 
-	read_lock_bh(&qdisc_tree_lock);
+	read_lock(&qdisc_tree_lock);
 	list_for_each_entry(q, &dev->qdisc_list, list) {
 		if (t < s_t || !q->ops->cl_ops ||
 		    (tcm->tcm_parent &&
@@ -1096,7 +1096,7 @@ static int tc_dump_tclass(struct sk_buff *skb, struct netlink_callback *cb)
 			break;
 		t++;
 	}
-	read_unlock_bh(&qdisc_tree_lock);
+	read_unlock(&qdisc_tree_lock);
 
 	cb->args[0] = t;