[Patch net 1/3] net_sched: fix a race condition in tcindex_destroy()

[Cong Wang <xiyou.wangcong@gmail.com>]

tcindex_destroy() invokes tcindex_destroy_element() via
a walker to delete each filter result in its perfect hash
table, and tcindex_destroy_element() calls tcindex_delete()
which schedules tcf RCU works to do the final deletion work.
Unfortunately this races with the RCU callback
__tcindex_destroy(), which could lead to use-after-free as
reported by Adrian.

Fix this by migrating this RCU callback to tcf RCU work too,
as that workqueue is ordered, we will not have use-after-free.

This change requires us to store a net pointer inside struct
tcindex_data, to avoid the known race with tc_action_net_exit().

Fixes: 27ce4f05e2ab ("net_sched: use tcf_queue_work() in tcindex filter")
Reported-by: Adrian <bugs@abtelecom.ro>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/sched/cls_tcindex.c | 46 ++++++++++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 9ccc93f257db..14e6d80dd58e 100644
--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -48,7 +48,8 @@ struct tcindex_data {
 	u32 hash;		/* hash table size; 0 if undefined */
 	u32 alloc_hash;		/* allocated size */
 	u32 fall_through;	/* 0: only classify if explicit match */
-	struct rcu_head rcu;
+	struct net *net;
+	struct rcu_work rwork;
 };
 
 static inline int tcindex_filter_is_set(struct tcindex_filter_result *r)
@@ -229,15 +230,23 @@ static int tcindex_destroy_element(struct tcf_proto *tp,
 	return tcindex_delete(tp, arg, &last, NULL);
 }
 
-static void __tcindex_destroy(struct rcu_head *head)
+static void __tcindex_destroy(struct tcindex_data *p)
 {
-	struct tcindex_data *p = container_of(head, struct tcindex_data, rcu);
-
 	kfree(p->perfect);
 	kfree(p->h);
 	kfree(p);
 }
 
+static void tcindex_destroy_work(struct work_struct *work)
+{
+	struct tcindex_data *p = container_of(to_rcu_work(work),
+					      struct tcindex_data,
+					      rwork);
+
+	put_net(p->net);
+	__tcindex_destroy(p);
+}
+
 static inline int
 valid_perfect_hash(struct tcindex_data *p)
 {
@@ -258,14 +267,22 @@ static int tcindex_filter_result_init(struct tcindex_filter_result *r)
 	return tcf_exts_init(&r->exts, TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);
 }
 
-static void __tcindex_partial_destroy(struct rcu_head *head)
+static void __tcindex_partial_destroy(struct tcindex_data *p)
 {
-	struct tcindex_data *p = container_of(head, struct tcindex_data, rcu);
-
 	kfree(p->perfect);
 	kfree(p);
 }
 
+static void tcindex_partial_destroy_work(struct work_struct *work)
+{
+	struct tcindex_data *p = container_of(to_rcu_work(work),
+					      struct tcindex_data,
+					      rwork);
+
+	put_net(p->net);
+	__tcindex_partial_destroy(p);
+}
+
 static void tcindex_free_perfect_hash(struct tcindex_data *cp)
 {
 	int i;
@@ -333,6 +350,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 	cp->alloc_hash = p->alloc_hash;
 	cp->fall_through = p->fall_through;
 	cp->tp = tp;
+	cp->net = net;
 
 	if (p->perfect) {
 		int i;
@@ -477,8 +495,13 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 		rcu_assign_pointer(*fp, f);
 	}
 
-	if (oldp)
-		call_rcu(&oldp->rcu, __tcindex_partial_destroy);
+	if (oldp) {
+		if (oldp->net && maybe_get_net(oldp->net))
+			tcf_queue_work(&oldp->rwork,
+				       tcindex_partial_destroy_work);
+		else
+			__tcindex_partial_destroy(oldp);
+	}
 	return 0;
 
 errout_alloc:
@@ -570,7 +593,10 @@ static void tcindex_destroy(struct tcf_proto *tp,
 	walker.fn = tcindex_destroy_element;
 	tcindex_walk(tp, &walker);
 
-	call_rcu(&p->rcu, __tcindex_destroy);
+	if (maybe_get_net(p->net))
+		tcf_queue_work(&p->rwork, tcindex_destroy_work);
+	else
+		__tcindex_destroy(p);
 }
 
 
-- 
2.20.1