[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 a19eff12cf78..0b6489291140 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;