netdev - Re: [PATCH net] Panic when tc_lookup_action_n finds a partially initialized action.

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Message-ID: <92102cf9-9f27-3a9f-06b6-f45201dbc55c@mojatatu.com>
Date:   Sun, 2 Oct 2016 21:18:06 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Krister Johansen <kjlx@...pleofstupid.com>
Cc:     netdev@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH net] Panic when tc_lookup_action_n finds a partially
 initialized action.

On 16-10-01 11:13 PM, Krister Johansen wrote:
> A tc_action_ops structure is visibile as soon as it is placed in the
> act_base list.  When tcf_regsiter_action adds an item to this list and
> drops act_mod_lock, registration is not complete until
> register_pernet_subsys() finishes.
>
> If two threads attempt to modify a tc action in a way that triggers a
> module load, the thread that wins the race ends up defeferencing a NULL
> pointer after tcf_action_init_1() invokes a_o->init().  In the
> particular case that this submitter encountered, the panic occurred in
> tcf_gact_init() when net_generic() returned a NULL tc_action_net
> pointer.  The gact_net_id needed to fetch the correct pointer was not
> yet set, because the register_pernet_subsys() call was pending in
> another thread.
>
> Fixes: ddf97ccdd7cb ("net_sched: add network namespace support for tc actions")
> Signed-off-by: Krister Johansen <kjlx@...pleofstupid.com>

Looks reasonable to me but will let Cong a closer look since he added
that code.

cheers,
jamal