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    Subject[PATCH 4.19 115/152] net_sched: fix a race condition in tcindex_destroy()
    Date
    4.19-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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