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

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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>
This commit is contained in:
Patrick McHardy 2006-09-27 16:45:45 -07:00 committed by David S. Miller
parent 787e0617e5
commit 85670cc1fa
4 changed files with 39 additions and 61 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
net/core/dev.c
View File

@ -1480,14 +1480,16 @@ gso:
if (q->enqueue) {
/* Grab device queue */
spin_lock(&dev->queue_lock);
q = dev->qdisc;
if (q->enqueue) {
rc = q->enqueue(skb, q);
qdisc_run(dev);
spin_unlock(&dev->queue_lock);
rc = q->enqueue(skb, q);
qdisc_run(dev);
rc = rc == NET_XMIT_BYPASS ? NET_XMIT_SUCCESS : rc;
goto out;
}
spin_unlock(&dev->queue_lock);
rc = rc == NET_XMIT_BYPASS ? NET_XMIT_SUCCESS : rc;
goto out;
}
/* The device has no queue. Common case for software devices:

4
net/sched/cls_api.c
View File

@ -401,7 +401,7 @@ static int tc_dump_tfilter(struct sk_buff *skb, struct netlink_callback *cb)
if ((dev = dev_get_by_index(tcm->tcm_ifindex)) == NULL)
return skb->len;
read_lock_bh(&qdisc_tree_lock);
read_lock(&qdisc_tree_lock);
if (!tcm->tcm_parent)
q = dev->qdisc_sleeping;
else
@ -458,7 +458,7 @@ errout:
if (cl)
cops->put(q, cl);
out:
read_unlock_bh(&qdisc_tree_lock);
read_unlock(&qdisc_tree_lock);
dev_put(dev);
return skb->len;
}

16
net/sched/sch_api.c
View File

@ -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;

66
net/sched/sch_generic.c
View File

@ -45,11 +45,10 @@
The idea is the following:
- enqueue, dequeue are serialized via top level device
spinlock dev->queue_lock.
- tree walking is protected by read_lock_bh(qdisc_tree_lock)
- tree walking is protected by read_lock(qdisc_tree_lock)
and this lock is used only in process context.
- updates to tree are made under rtnl semaphore or
from softirq context (__qdisc_destroy rcu-callback)
hence this lock needs local bh disabling.
- updates to tree are made only under rtnl semaphore,
hence this lock may be made without local bh disabling.
qdisc_tree_lock must be grabbed BEFORE dev->queue_lock!
*/
@ -57,14 +56,14 @@ DEFINE_RWLOCK(qdisc_tree_lock);
void qdisc_lock_tree(struct net_device *dev)
{
write_lock_bh(&qdisc_tree_lock);
write_lock(&qdisc_tree_lock);
spin_lock_bh(&dev->queue_lock);
}
void qdisc_unlock_tree(struct net_device *dev)
{
spin_unlock_bh(&dev->queue_lock);
write_unlock_bh(&qdisc_tree_lock);
write_unlock(&qdisc_tree_lock);
}
/*
@ -483,20 +482,6 @@ void qdisc_reset(struct Qdisc *qdisc)
static void __qdisc_destroy(struct rcu_head *head)
{
struct Qdisc *qdisc = container_of(head, struct Qdisc, q_rcu);
struct Qdisc_ops *ops = qdisc->ops;
#ifdef CONFIG_NET_ESTIMATOR
gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
#endif
write_lock(&qdisc_tree_lock);
if (ops->reset)
ops->reset(qdisc);
if (ops->destroy)
ops->destroy(qdisc);
write_unlock(&qdisc_tree_lock);
module_put(ops->owner);
dev_put(qdisc->dev);
kfree((char *) qdisc - qdisc->padded);
}
@ -504,32 +489,23 @@ static void __qdisc_destroy(struct rcu_head *head)
void qdisc_destroy(struct Qdisc *qdisc)
{
struct list_head cql = LIST_HEAD_INIT(cql);
struct Qdisc *cq, *q, *n;
struct Qdisc_ops *ops = qdisc->ops;
if (qdisc->flags & TCQ_F_BUILTIN ||
!atomic_dec_and_test(&qdisc->refcnt))
!atomic_dec_and_test(&qdisc->refcnt))
return;
if (!list_empty(&qdisc->list)) {
if (qdisc->ops->cl_ops == NULL)
list_del(&qdisc->list);
else
list_move(&qdisc->list, &cql);
}
/* unlink inner qdiscs from dev->qdisc_list immediately */
list_for_each_entry(cq, &cql, list)
list_for_each_entry_safe(q, n, &qdisc->dev->qdisc_list, list)
if (TC_H_MAJ(q->parent) == TC_H_MAJ(cq->handle)) {
if (q->ops->cl_ops == NULL)
list_del_init(&q->list);
else
list_move_tail(&q->list, &cql);
}
list_for_each_entry_safe(cq, n, &cql, list)
list_del_init(&cq->list);
list_del(&qdisc->list);
#ifdef CONFIG_NET_ESTIMATOR
gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
#endif
if (ops->reset)
ops->reset(qdisc);
if (ops->destroy)
ops->destroy(qdisc);
module_put(ops->owner);
dev_put(qdisc->dev);
call_rcu(&qdisc->q_rcu, __qdisc_destroy);
}
@ -549,15 +525,15 @@ void dev_activate(struct net_device *dev)
printk(KERN_INFO "%s: activation failed\n", dev->name);
return;
}
write_lock_bh(&qdisc_tree_lock);
write_lock(&qdisc_tree_lock);
list_add_tail(&qdisc->list, &dev->qdisc_list);
write_unlock_bh(&qdisc_tree_lock);
write_unlock(&qdisc_tree_lock);
} else {
qdisc = &noqueue_qdisc;
}
write_lock_bh(&qdisc_tree_lock);
write_lock(&qdisc_tree_lock);
dev->qdisc_sleeping = qdisc;
write_unlock_bh(&qdisc_tree_lock);
write_unlock(&qdisc_tree_lock);
}
if (!netif_carrier_ok(dev))