In commit 7aa0045dadb6 ("net_sched: introduce a workqueue for RCU callbacks of
tc filter")
I defer tcf_chain_flush() to a workqueue, this causes a use-after-free
because qdisc is already destroyed after we queue this work.
The tcf_block_put_deferred() is no longer necessary after we get RTNL
for each tc filter destroy work, no others could jump in at this point.
Same for tcf_chain_hold(), we are fully serialized now.
This also reduces one indirection therefore makes the code more
readable. Note this brings back a rcu_barrier(), however comparing
to the code prior to commit 7aa0045dadb6 we still reduced one
rcu_barrier(). For net-next, we can consider to refcnt tcf block to
avoid it.
Fixes: 7aa0045dadb6 ("net_sched: introduce a workqueue for RCU callbacks of tc
filter")
Cc: Daniel Borkmann <[email protected]>
Cc: Jiri Pirko <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: Jamal Hadi Salim <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
---
net/sched/cls_api.c | 37 ++++++++-----------------------------
1 file changed, 8 insertions(+), 29 deletions(-)
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 231181c602ed..b2d310745487 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -280,8 +280,8 @@ static void tcf_block_put_final(struct work_struct *work)
struct tcf_block *block = container_of(work, struct tcf_block, work);
struct tcf_chain *chain, *tmp;
- /* At this point, all the chains should have refcnt == 1. */
rtnl_lock();
+ /* Only chain 0 should be still here. */
list_for_each_entry_safe(chain, tmp, &block->chain_list, list)
tcf_chain_put(chain);
rtnl_unlock();
@@ -289,23 +289,17 @@ static void tcf_block_put_final(struct work_struct *work)
}
/* XXX: Standalone actions are not allowed to jump to any chain, and bound
- * actions should be all removed after flushing. However, filters are destroyed
- * in RCU callbacks, we have to hold the chains first, otherwise we would
- * always race with RCU callbacks on this list without proper locking.
+ * actions should be all removed after flushing. However, filters are now
+ * destroyed in tc filter workqueue with RTNL lock, they can not race here.
*/
-static void tcf_block_put_deferred(struct work_struct *work)
+void tcf_block_put(struct tcf_block *block)
{
- struct tcf_block *block = container_of(work, struct tcf_block, work);
- struct tcf_chain *chain;
+ struct tcf_chain *chain, *tmp;
- rtnl_lock();
- /* Hold a refcnt for all chains, except 0, in case they are gone. */
- list_for_each_entry(chain, &block->chain_list, list)
- if (chain->index)
- tcf_chain_hold(chain);
+ if (!block)
+ return;
- /* No race on the list, because no chain could be destroyed. */
- list_for_each_entry(chain, &block->chain_list, list)
+ list_for_each_entry_safe(chain, tmp, &block->chain_list, list)
tcf_chain_flush(chain);
INIT_WORK(&block->work, tcf_block_put_final);
@@ -314,21 +308,6 @@ static void tcf_block_put_deferred(struct work_struct
*work)
*/
rcu_barrier();
tcf_queue_work(&block->work);
- rtnl_unlock();
-}
-
-void tcf_block_put(struct tcf_block *block)
-{
- if (!block)
- return;
-
- INIT_WORK(&block->work, tcf_block_put_deferred);
- /* Wait for existing RCU callbacks to cool down, make sure their works
- * have been queued before this. We can not flush pending works here
- * because we are holding the RTNL lock.
- */
- rcu_barrier();
- tcf_queue_work(&block->work);
}
EXPORT_SYMBOL(tcf_block_put);
--
2.13.0
