Commit 9c29e361 authored Jul 03, 2020 by Paolo Abeni Committed by David S. Miller Jul 07, 2020

mptcp: fix DSS map generation on fin retransmission



The RFC 8684 mandates that no-data DATA FIN packets should carry
a DSS with 0 sequence number and data len equal to 1. Currently,
on FIN retransmission we re-use the existing mapping; if the previous
fin transmission was part of a partially acked data packet, we could
end-up writing in the egress packet a non-compliant DSS.

The above will be detected by a "Bad mapping" warning on the receiver
side.

This change addresses the issue explicitly checking for 0 len packet
when adding the DATA_FIN option.

Fixes: 6d0060f6 ("mptcp: Write MPTCP DSS headers to outgoing data packets")
Reported-by:  <syzbot+42a07faa5923cfaeb9c9@syzkaller.appspotmail.com>
Tested-by: Christoph Paasch <cpaasch@apple.com>
Reviewed-by: Christoph Paasch <cpaasch@apple.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5eff0690

net/mptcp/options.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -449,9 +449,9 @@ static bool mptcp_established_options_mp(struct sock sk, struct sk_buff skb,
		}

		static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
		struct mptcp_ext *ext)
		struct sk_buff skb, struct mptcp_ext ext)
		{
		if (!ext->use_map) {
		if (!ext->use_map \|\| !skb->len) {
		/* RFC6824 requires a DSS mapping with specific values
		* if DATA_FIN is set but no data payload is mapped
		*/
		@@ -503,7 +503,7 @@ static bool mptcp_established_options_dss(struct sock sk, struct sk_buff skb,
		opts->ext_copy = *mpext;

		if (skb && tcp_fin && subflow->data_fin_tx_enable)
		mptcp_write_data_fin(subflow, &opts->ext_copy);
		mptcp_write_data_fin(subflow, skb, &opts->ext_copy);
		ret = true;
		}

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