[MPTCP] Re: [PATCH net 2/2] mptcp: better msk-level shutdown.

[Eric Dumazet <eric.dumazet at gmail.com>]

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On 1/12/21 6:25 PM, Paolo Abeni wrote:
> Instead of re-implementing most of inet_shutdown, re-use
> such helper, and implement the MPTCP-specific bits at the
> 'proto' level.
> 
> The msk-level disconnect() can now be invoked, lets provide a
> suitable implementation.
> 
> As a side effect, this fixes bad state management for listener
> sockets. The latter could lead to division by 0 oops since
> commit ea4ca586b16f ("mptcp: refine MPTCP-level ack scheduling").
> 
> Fixes: 43b54c6ee382 ("mptcp: Use full MPTCP-level disconnect state machine")
> Fixes: ea4ca586b16f ("mptcp: refine MPTCP-level ack scheduling")
> Signed-off-by: Paolo Abeni <pabeni(a)redhat.com>
> ---
>  net/mptcp/protocol.c | 62 ++++++++++++--------------------------------
>  1 file changed, 17 insertions(+), 45 deletions(-)
> 
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index 2ff8c7caf74f..81faeff8f3bb 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -2642,11 +2642,12 @@ static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk)
>  
>  static int mptcp_disconnect(struct sock *sk, int flags)
>  {
> -	/* Should never be called.
> -	 * inet_stream_connect() calls ->disconnect, but that
> -	 * refers to the subflow socket, not the mptcp one.
> -	 */
> -	WARN_ON_ONCE(1);
> +	struct mptcp_subflow_context *subflow;
> +	struct mptcp_sock *msk = mptcp_sk(sk);
> +
> +	__mptcp_flush_join_list(msk);
> +	mptcp_for_each_subflow(msk, subflow)
> +		tcp_disconnect(mptcp_subflow_tcp_sock(subflow), flags);

Ouch.

tcp_disconnect() is supposed to be called with socket lock being held.

Really, CONFIG_LOCKDEP=y should have warned you :/