netdev - Re: [PATCH net] mptcp: fix data stream corruption

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Date:   Tue, 11 May 2021 09:17:52 -0700 (PDT)
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     Paolo Abeni <pabeni@...hat.com>
cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, mptcp@...ts.linux.dev,
        Maxim Galaganov <max@...ernet.ru>
Subject: Re: [PATCH net] mptcp: fix data stream corruption

On Tue, 11 May 2021, Paolo Abeni wrote:

> Maxim reported several issues when forcing a TCP transparent proxy
> to use the MPTCP protocol for the inbound connections. He also
> provided a clean reproducer.
>
> The problem boils down to 'mptcp_frag_can_collapse_to()' assuming
> that only MPTCP will use the given page_frag.
>
> If others - e.g. the plain TCP protocol - allocate page fragments,
> we can end-up re-using already allocated memory for mptcp_data_frag.
>
> Fix the issue ensuring that the to-be-expanded data fragment is
> located at the current page frag end.
>
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/178
> Reported-and-tested-by: Maxim Galaganov <max@...ernet.ru>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
> net/mptcp/protocol.c | 6 ++++++
> 1 file changed, 6 insertions(+)

Hi Paolo -

Should this also have a:

Fixes: 18b683bff89d ("mptcp: queue data for mptcp level retransmission")

?


-Mat


>
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index 29a2d690d8d5..2d21a4793d9d 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -879,12 +879,18 @@ static bool mptcp_skb_can_collapse_to(u64 write_seq,
> 	       !mpext->frozen;
> }
>
> +/* we can append data to the given data frag if:
> + * - there is space available in the backing page_frag
> + * - the data frag tail matches the current page_frag free offset
> + * - the data frag end sequence number matches the current write seq
> + */
> static bool mptcp_frag_can_collapse_to(const struct mptcp_sock *msk,
> 				       const struct page_frag *pfrag,
> 				       const struct mptcp_data_frag *df)
> {
> 	return df && pfrag->page == df->page &&
> 		pfrag->size - pfrag->offset > 0 &&
> +		pfrag->offset == (df->offset + df->data_len) &&
> 		df->data_seq + df->data_len == msk->write_seq;
> }
>
> -- 
> 2.26.2
>
>
>

--
Mat Martineau
Intel