Commit f3589be0 authored by Paolo Abeni's avatar Paolo Abeni Committed by Jakub Kicinski
Browse files

mptcp: never shrink offered window 



As per RFC, the offered MPTCP-level window should never shrink.
While we currently track the right edge, we don't enforce the
above constraint on the wire.
Additionally, concurrent xmit on different subflows can end-up in
erroneous right edge update.
Address the above explicitly updating the announced window and
protecting the update with an additional atomic operation (sic)

Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
Signed-off-by: default avatarMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent ea66758c

net/mptcp/options.c

+45 −7
Original line number Diff line number Diff line
@@ -1224,20 +1224,58 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb) 
	return true;

}



static void mptcp_set_rwin(const struct tcp_sock *tp)

static void mptcp_set_rwin(struct tcp_sock *tp, struct tcphdr *th)

{

	const struct sock *ssk = (const struct sock *)tp;

	const struct mptcp_subflow_context *subflow;

	struct mptcp_subflow_context *subflow;

	u64 ack_seq, rcv_wnd_old, rcv_wnd_new;

	struct mptcp_sock *msk;

	u64 ack_seq;

	u32 new_win;

	u64 win;



	subflow = mptcp_subflow_ctx(ssk);

	msk = mptcp_sk(subflow->conn);



	ack_seq = READ_ONCE(msk->ack_seq) + tp->rcv_wnd;

	ack_seq = READ_ONCE(msk->ack_seq);

	rcv_wnd_new = ack_seq + tp->rcv_wnd;



	rcv_wnd_old = atomic64_read(&msk->rcv_wnd_sent);

	if (after64(rcv_wnd_new, rcv_wnd_old)) {

		u64 rcv_wnd;



	if (after64(ack_seq, READ_ONCE(msk->rcv_wnd_sent)))

		WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);

		for (;;) {

			rcv_wnd = atomic64_cmpxchg(&msk->rcv_wnd_sent, rcv_wnd_old, rcv_wnd_new);



			if (rcv_wnd == rcv_wnd_old)

				break;

			if (before64(rcv_wnd_new, rcv_wnd))

				goto raise_win;

			rcv_wnd_old = rcv_wnd;

		}

		return;

	}



	if (rcv_wnd_new != rcv_wnd_old) {

raise_win:

		win = rcv_wnd_old - ack_seq;

		tp->rcv_wnd = min_t(u64, win, U32_MAX);

		new_win = tp->rcv_wnd;



		/* Make sure we do not exceed the maximum possible

		 * scaled window.

		 */

		if (unlikely(th->syn))

			new_win = min(new_win, 65535U) << tp->rx_opt.rcv_wscale;

		if (!tp->rx_opt.rcv_wscale &&

		    sock_net(ssk)->ipv4.sysctl_tcp_workaround_signed_windows)

			new_win = min(new_win, MAX_TCP_WINDOW);

		else

			new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));



		/* RFC1323 scaling applied */

		new_win >>= tp->rx_opt.rcv_wscale;

		th->window = htons(new_win);

	}

}



u16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum)
@@ -1554,7 +1592,7 @@ void mptcp_write_options(struct tcphdr *th, __be32 *ptr, struct tcp_sock *tp, 
	}



	if (tp)

		mptcp_set_rwin(tp);

		mptcp_set_rwin(tp, th);

}



__be32 mptcp_get_reset_option(const struct sk_buff *skb)

net/mptcp/protocol.c

+4 −4
Original line number Diff line number Diff line
@@ -216,7 +216,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb) 


	seq = MPTCP_SKB_CB(skb)->map_seq;

	end_seq = MPTCP_SKB_CB(skb)->end_seq;

	max_seq = READ_ONCE(msk->rcv_wnd_sent);

	max_seq = atomic64_read(&msk->rcv_wnd_sent);



	pr_debug("msk=%p seq=%llx limit=%llx empty=%d", msk, seq, max_seq,

		 RB_EMPTY_ROOT(&msk->out_of_order_queue));
@@ -225,7 +225,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb) 
		mptcp_drop(sk, skb);

		pr_debug("oow by %lld, rcv_wnd_sent %llu\n",

			 (unsigned long long)end_seq - (unsigned long)max_seq,

			 (unsigned long long)msk->rcv_wnd_sent);

			 (unsigned long long)atomic64_read(&msk->rcv_wnd_sent));

		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_NODSSWINDOW);

		return;

	}
@@ -3004,7 +3004,7 @@ struct sock *mptcp_sk_clone(const struct sock *sk, 
		mptcp_crypto_key_sha(msk->remote_key, NULL, &ack_seq);

		ack_seq++;

		WRITE_ONCE(msk->ack_seq, ack_seq);

		WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);

		atomic64_set(&msk->rcv_wnd_sent, ack_seq);

	}



	sock_reset_flag(nsk, SOCK_RCU_FREE);
@@ -3297,9 +3297,9 @@ void mptcp_finish_connect(struct sock *ssk) 
	WRITE_ONCE(msk->write_seq, subflow->idsn + 1);

	WRITE_ONCE(msk->snd_nxt, msk->write_seq);

	WRITE_ONCE(msk->ack_seq, ack_seq);

	WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);

	WRITE_ONCE(msk->can_ack, 1);

	WRITE_ONCE(msk->snd_una, msk->write_seq);

	atomic64_set(&msk->rcv_wnd_sent, ack_seq);



	mptcp_pm_new_connection(msk, ssk, 0);

net/mptcp/protocol.h

+1 −1
Original line number Diff line number Diff line
@@ -257,7 +257,7 @@ struct mptcp_sock { 
	u64		write_seq;

	u64		snd_nxt;

	u64		ack_seq;

	u64		rcv_wnd_sent;

	atomic64_t	rcv_wnd_sent;

	u64		rcv_data_fin_seq;

	int		rmem_fwd_alloc;

	struct sock	*last_snd;