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Subject[PATCH 4.20 140/183] net_sched: fix a race condition in tcindex_destroy()
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Cong Wang <xiyou.wangcong@gmail.com>

[ Upstream commit 8015d93ebd27484418d4952284fd02172fa4b0b2 ]

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.

Note, we don't need to hold netns refcnt because we don't call
tcf_exts_destroy() here.

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/cls_tcindex.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -48,7 +48,7 @@ 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 rcu_work rwork;
};

static inline int tcindex_filter_is_set(struct tcindex_filter_result *r)
@@ -229,9 +229,11 @@ static int tcindex_destroy_element(struc
return tcindex_delete(tp, arg, &last, NULL);
}

-static void __tcindex_destroy(struct rcu_head *head)
+static void tcindex_destroy_work(struct work_struct *work)
{
- struct tcindex_data *p = container_of(head, struct tcindex_data, rcu);
+ struct tcindex_data *p = container_of(to_rcu_work(work),
+ struct tcindex_data,
+ rwork);

kfree(p->perfect);
kfree(p->h);
@@ -258,9 +260,11 @@ static int tcindex_filter_result_init(st
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_work(struct work_struct *work)
{
- struct tcindex_data *p = container_of(head, struct tcindex_data, rcu);
+ struct tcindex_data *p = container_of(to_rcu_work(work),
+ struct tcindex_data,
+ rwork);

kfree(p->perfect);
kfree(p);
@@ -478,7 +482,7 @@ tcindex_set_parms(struct net *net, struc
}

if (oldp)
- call_rcu(&oldp->rcu, __tcindex_partial_destroy);
+ tcf_queue_work(&oldp->rwork, tcindex_partial_destroy_work);
return 0;

errout_alloc:
@@ -570,7 +574,7 @@ static void tcindex_destroy(struct tcf_p
walker.fn = tcindex_destroy_element;
tcindex_walk(tp, &walker);

- call_rcu(&p->rcu, __tcindex_destroy);
+ tcf_queue_work(&p->rwork, tcindex_destroy_work);
}



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