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    Subject[PATCH 4.14 112/115] net: sched: fix crash when deleting secondary chains
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Roman Kapl <code@rkapl.cz>

    commit d7aa04a5e82b4f254d306926c81eae8df69e5200 upstream.

    If you flush (delete) a filter chain other than chain 0 (such as when
    deleting the device), the kernel may run into a use-after-free. The
    chain refcount must not be decremented unless we are sure we are done
    with the chain.

    To reproduce the bug, run:
    ip link add dtest type dummy
    tc qdisc add dev dtest ingress
    tc filter add dev dtest chain 1 parent ffff: flower
    ip link del dtest

    Introduced in: commit f93e1cdcf42c ("net/sched: fix filter flushing"),
    but unless you have KAsan or luck, you won't notice it until
    commit 0dadc117ac8b ("cls_flower: use tcf_exts_get_net() before call_rcu()")

    Fixes: f93e1cdcf42c ("net/sched: fix filter flushing")
    Acked-by: Jiri Pirko <jiri@mellanox.com>
    Signed-off-by: Roman Kapl <code@rkapl.cz>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Cc: Cong Wang <xiyou.wangcong@gmail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/sched/cls_api.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/net/sched/cls_api.c
    +++ b/net/sched/cls_api.c
    @@ -197,14 +197,15 @@ static struct tcf_chain *tcf_chain_creat

    static void tcf_chain_flush(struct tcf_chain *chain)
    {
    - struct tcf_proto *tp;
    + struct tcf_proto *tp = rtnl_dereference(chain->filter_chain);

    if (chain->p_filter_chain)
    RCU_INIT_POINTER(*chain->p_filter_chain, NULL);
    - while ((tp = rtnl_dereference(chain->filter_chain)) != NULL) {
    + while (tp) {
    RCU_INIT_POINTER(chain->filter_chain, tp->next);
    - tcf_chain_put(chain);
    tcf_proto_destroy(tp);
    + tp = rtnl_dereference(chain->filter_chain);
    + tcf_chain_put(chain);
    }
    }


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