Commit 729cd643 authored May 15, 2020 by Paolo Abeni Committed by David S. Miller May 15, 2020

mptcp: cope better with MP_JOIN failure



Currently, on MP_JOIN failure we reset the child
socket, but leave the request socket untouched.

tcp_check_req will deal with it according to the
'tcp_abort_on_overflow' sysctl value - by default the
req socket will stay alive.

The above leads to inconsistent behavior on MP JOIN
failure, and bad listener overflow accounting.

This patch addresses the issue leveraging the infrastructure
just introduced to ask the TCP stack to drop the req on
failure.

The child socket is not freed anymore by subflow_syn_recv_sock(),
instead it's moved to a dead state and will be disposed by the
next sock_put done by the TCP stack, so that listener overflow
accounting is not affected by MP JOIN failure.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Christoph Paasch <cpaasch@apple.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 2f8a397d

net/mptcp/subflow.c

+9 −6

Original line number	Diff line number	Diff line
		@@ -478,7 +478,7 @@ create_child:
		*/
		if (!ctx \|\| fallback) {
		if (fallback_is_fatal)
		goto close_child;
		goto dispose_child;

		if (ctx) {
		subflow_ulp_fallback(child, ctx);
		@@ -507,11 +507,11 @@ create_child:

		owner = mptcp_token_get_sock(ctx->token);
		if (!owner)
		goto close_child;
		goto dispose_child;

		ctx->conn = (struct sock *)owner;
		if (!mptcp_finish_join(child))
		goto close_child;
		goto dispose_child;

		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKRX);
		tcp_rsk(req)->drop_req = true;
		@@ -531,11 +531,14 @@ out:
		!mptcp_subflow_ctx(child)->conn));
		return child;

		close_child:
		dispose_child:
		tcp_rsk(req)->drop_req = true;
		tcp_send_active_reset(child, GFP_ATOMIC);
		inet_csk_prepare_forced_close(child);
		inet_csk_prepare_for_destroy_sock(child);
		tcp_done(child);
		return NULL;

		/* The last child reference will be released by the caller */
		return child;
		}

		static struct inet_connection_sock_af_ops subflow_specific;

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