mptcp: process pending subflow error on close

mptcp: process pending subflow error on close

commit 9f1a98813b4b686482e5ef3c9d998581cace0ba6 upstream.

On incoming TCP reset, subflow closing could happen before error
propagation. That in turn could cause the socket error being ignored,
and a missing socket state transition, as reported by Daire-Byrne.

Address the issues explicitly checking for subflow socket error at
close time. To avoid code duplication, factor-out of __mptcp_error_report()
a new helper implementing the relevant bits.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/429
Fixes: 15cc10453398 ("mptcp: deliver ssk errors to msk")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>