mptcp: properly account bulk freed memory

After commit 879526030c8b ("mptcp: protect the rx path with
the msk socket spinlock") the rmem currently used by a given
msk is really sk_rmem_alloc - rmem_released.

The safety check in mptcp_data_ready() does not take the above
in due account, as a result legit incoming data is kept in
subflow receive queue with no reason, delaying or blocking
MPTCP-level ack generation.

This change addresses the issue introducing a new helper to fetch
the rmem memory and using it as needed. Additionally add a MIB
counter for the exceptional event described above - the peer is
misbehaving.

Finally, introduce the required annotation when rmem_released is
updated.

Fixes: 879526030c8b ("mptcp: protect the rx path with the msk socket spinlock")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/211
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 193466c9b549..0663cb12b448 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -37,6 +37,7 @@ enum linux_mptcp_mib_field {
 	MPTCP_MIB_RMSUBFLOW,		/* Remove a subflow */
 	MPTCP_MIB_MPPRIOTX,		/* Transmit a MP_PRIO */
 	MPTCP_MIB_MPPRIORX,		/* Received a MP_PRIO */
+	MPTCP_MIB_RCVPRUNED,		/* Incoming packet dropped due to memory limit */
 	__MPTCP_MIB_MAX
 };