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SubjectRe: [PATCH v5] sctp: fix refcount bug in sctp_wfree
sorry about missing a line. please ignore this.
I'll resend the patch.

On Fri, Mar 27, 2020 at 9:19 AM Qiujun Huang <hqjagain@gmail.com> wrote:
>
> We should iterate over the datamsgs to modify
> 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@syzkaller.appspotmail.com
> Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
> ---
> net/sctp/socket.c | 30 ++++++++++++++++++++++--------
> 1 file changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 1b56fc440606..75acbd5d4597 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -147,29 +147,43 @@ static void sctp_clear_owner_w(struct sctp_chunk *chunk)
> skb_orphan(chunk->skb);
> }
>
> +#define traverse_and_process() \
> +do { \
> + msg = chunk->msg; \
> + if (msg == prev_msg) \
> + continue; \
> + list_for_each_entry(c, &msg->chunks, frag_list) { \
> + if ((clear && asoc->base.sk == c->skb->sk) || \
> + (!clear && asoc->base.sk != c->skb->sk)) \
> + cb(c); \
> + } \
> +} while (0)
> +
> static void sctp_for_each_tx_datachunk(struct sctp_association *asoc,
> + bool clear,
> void (*cb)(struct sctp_chunk *))
>
> {
> + struct sctp_datamsg *msg, *prev_msg = NULL;
> struct sctp_outq *q = &asoc->outqueue;
> + struct sctp_chunk *chunk, *c;
> struct sctp_transport *t;
> - struct sctp_chunk *chunk;
>
> list_for_each_entry(t, &asoc->peer.transport_addr_list, transports)
> list_for_each_entry(chunk, &t->transmitted, transmitted_list)
> - cb(chunk);
> + traverse_and_process();
>
> list_for_each_entry(chunk, &q->retransmit, transmitted_list)
> - cb(chunk);
> + traverse_and_process();
>
> list_for_each_entry(chunk, &q->sacked, transmitted_list)
> - cb(chunk);
> + traverse_and_process();
>
> list_for_each_entry(chunk, &q->abandoned, transmitted_list)
> - cb(chunk);
> + traverse_and_process();
>
> list_for_each_entry(chunk, &q->out_chunk_list, list)
> - cb(chunk);
> + traverse_and_process();
> }
>
> static void sctp_for_each_rx_skb(struct sctp_association *asoc, struct sock *sk,
> @@ -9574,9 +9588,9 @@ static int sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
> * paths won't try to lock it and then oldsk.
> */
> lock_sock_nested(newsk, SINGLE_DEPTH_NESTING);
> - sctp_for_each_tx_datachunk(assoc, sctp_clear_owner_w);
> + sctp_for_each_tx_datachunk(assoc, true, sctp_clear_owner_w);
> sctp_assoc_migrate(assoc, newsk);
> - sctp_for_each_tx_datachunk(assoc, sctp_set_owner_w);
> + sctp_for_each_tx_datachunk(assoc, false, sctp_set_owner_w);
>
> /* If the association on the newsk is already closed before accept()
> * is called, set RCV_SHUTDOWN flag.
> --
> 2.17.1
>

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