linux-kernel - Re: [PATCH v6] sctp: fix refcount bug in sctp

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Date:   Fri, 27 Mar 2020 01:05:34 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Qiujun Huang <hqjagain@...il.com>
Cc:     davem@...emloft.net, vyasevich@...il.com, nhorman@...driver.com,
        kuba@...nel.org, linux-sctp@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        anenbupt@...il.com
Subject: Re: [PATCH v6] sctp: fix refcount bug in sctp_wfree

On Fri, Mar 27, 2020 at 11:07:51AM +0800, Qiujun Huang wrote:
> We should iterate over the datamsgs to move
> all chunks(skbs) to newsk.
> 
> The following case cause the bug:
> for the trouble SKB, it was in outq->transmitted list
> 
> sctp_outq_sack
>         sctp_check_transmitted
>                 SKB was moved to outq->sacked list
>         then throw away the sack queue
>                 SKB was deleted from outq->sacked
> (but it was held by datamsg at sctp_datamsg_to_asoc
> So, sctp_wfree was not called here)
> 
> then migrate happened
> 
>         sctp_for_each_tx_datachunk(
>         sctp_clear_owner_w);
>         sctp_assoc_migrate();
>         sctp_for_each_tx_datachunk(
>         sctp_set_owner_w);
> SKB was not in the outq, and was not changed to newsk
> 
> finally
> 
> __sctp_outq_teardown
>         sctp_chunk_put (for another skb)
>                 sctp_datamsg_put
>                         __kfree_skb(msg->frag_list)
>                                 sctp_wfree (for SKB)
> 	SKB->sk was still oldsk (skb->sk != asoc->base.sk).
> 
> Reported-and-tested-by: syzbot+cea71eec5d6de256d54d@...kaller.appspotmail.com
> Signed-off-by: Qiujun Huang <hqjagain@...il.com>

Acked-by: Marcelo Ricardo Leitner <mleitner@...hat.com>
Thanks Qiujun.