net, sched: convert Qdisc.refcnt from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <[email protected]>
Signed-off-by: Hans Liljestrand <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: David Windsor <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

include/net/sch_generic.h

@@ -9,6 +9,7 @@
 #include <linux/percpu.h>
 #include <linux/dynamic_queue_limits.h>
 #include <linux/list.h>
+#include <linux/refcount.h>
 #include <net/gen_stats.h>
 #include <net/rtnetlink.h>
 
@@ -95,7 +96,7 @@ struct Qdisc {
  struct sk_buff *skb_bad_txq;
  struct rcu_head rcu_head;
  int padded;
- atomic_t refcnt;
+ refcount_t refcnt;
 
  spinlock_t busylock ____cacheline_aligned_in_smp;
 };

net/sched/sch_api.c

@@ -839,7 +839,7 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent,
 
  old = dev_graft_qdisc(dev_queue, new);
  if (new && i > 0)
- atomic_inc(&new->refcnt);
+ refcount_inc(&new->refcnt);
 
  if (!ingress)
  qdisc_destroy(old);
@@ -850,7 +850,7 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent,
  notify_and_destroy(net, skb, n, classid,
  dev->qdisc, new);
  if (new && !new->ops->attach)
- atomic_inc(&new->refcnt);
+ refcount_inc(&new->refcnt);
  dev->qdisc = new ? : &noop_qdisc;
 
  if (new && new->ops->attach)
@@ -1259,7 +1259,7 @@ static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
  if (q == p ||
  (p && check_loop(q, p, 0)))
  return -ELOOP;
- atomic_inc(&q->refcnt);
+ refcount_inc(&q->refcnt);
  goto graft;
  } else {
  if (!q)
@@ -1374,7 +1374,7 @@ static int tc_fill_qdisc(struct sk_buff *skb, struct Qdisc *q, u32 clid,
  tcm->tcm_ifindex = qdisc_dev(q)->ifindex;
  tcm->tcm_parent = clid;
  tcm->tcm_handle = q->handle;
- tcm->tcm_info = atomic_read(&q->refcnt);
+ tcm->tcm_info = refcount_read(&q->refcnt);
  if (nla_put_string(skb, TCA_KIND, q->ops->id))
  goto nla_put_failure;
  if (q->ops->dump && q->ops->dump(q, skb) < 0)

net/sched/sch_generic.c

@@ -633,7 +633,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
  sch->dequeue = ops->dequeue;
  sch->dev_queue = dev_queue;
  dev_hold(dev);
- atomic_set(&sch->refcnt, 1);
+ refcount_set(&sch->refcnt, 1);
 
  return sch;
 errout:
@@ -701,7 +701,7 @@ void qdisc_destroy(struct Qdisc *qdisc)
  const struct Qdisc_ops *ops = qdisc->ops;
 
  if (qdisc->flags & TCQ_F_BUILTIN ||
- !atomic_dec_and_test(&qdisc->refcnt))
+ !refcount_dec_and_test(&qdisc->refcnt))
  return;
 
 #ifdef CONFIG_NET_SCHED
@@ -739,7 +739,7 @@ struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue,
  spin_lock_bh(root_lock);
 
  /* Prune old scheduler */
- if (oqdisc && atomic_read(&oqdisc->refcnt) <= 1)
+ if (oqdisc && refcount_read(&oqdisc->refcnt) <= 1)
  qdisc_reset(oqdisc);
 
  /* ... and graft new one */
@@ -785,7 +785,7 @@ static void attach_default_qdiscs(struct net_device *dev)
  dev->priv_flags & IFF_NO_QUEUE) {
  netdev_for_each_tx_queue(dev, attach_one_default_qdisc, NULL);
  dev->qdisc = txq->qdisc_sleeping;
- atomic_inc(&dev->qdisc->refcnt);
+ refcount_inc(&dev->qdisc->refcnt);
  } else {
  qdisc = qdisc_create_dflt(txq, &mq_qdisc_ops, TC_H_ROOT);
  if (qdisc) {