text: /* RxRPC packet reception
   *
   * Copyright (C) 2007, 2016 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/module.h>
  #include <linux/net.h>
  #include <linux/skbuff.h>
  #include <linux/errqueue.h>
  #include <linux/udp.h>
  #include <linux/in.h>
  #include <linux/in6.h>
  #include <linux/icmp.h>
  #include <linux/gfp.h>
  #include <net/sock.h>
  #include <net/af_rxrpc.h>
  #include <net/ip.h>
  #include <net/udp.h>
  #include <net/net_namespace.h>
  #include "ar-internal.h"
  
  static void rxrpc_proto_abort(const char *why,
  			      struct rxrpc_call *call, rxrpc_seq_t seq)
  {
  	if (rxrpc_abort_call(why, call, seq, RX_PROTOCOL_ERROR, EBADMSG)) {
  		set_bit(RXRPC_CALL_EV_ABORT, &call->events);
  		rxrpc_queue_call(call);
  	}
  }
  
  /*
   * Do TCP-style congestion management [RFC 5681].
   */
  static void rxrpc_congestion_management(struct rxrpc_call *call,
  					struct sk_buff *skb,
  					struct rxrpc_ack_summary *summary,
  					rxrpc_serial_t acked_serial)
  {
  	enum rxrpc_congest_change change = rxrpc_cong_no_change;
  	unsigned int cumulative_acks = call->cong_cumul_acks;
  	unsigned int cwnd = call->cong_cwnd;
  	bool resend = false;
  
  	summary->flight_size =
  		(call->tx_top - call->tx_hard_ack) - summary->nr_acks;
  
  	if (test_and_clear_bit(RXRPC_CALL_RETRANS_TIMEOUT, &call->flags)) {
  		summary->retrans_timeo = true;
  		call->cong_ssthresh = max_t(unsigned int,
  					    summary->flight_size / 2, 2);
  		cwnd = 1;
  		if (cwnd >= call->cong_ssthresh &&
  		    call->cong_mode == RXRPC_CALL_SLOW_START) {
  			call->cong_mode = RXRPC_CALL_CONGEST_AVOIDANCE;
  			call->cong_tstamp = skb->tstamp;
  			cumulative_acks = 0;
  		}
  	}
  
  	cumulative_acks += summary->nr_new_acks;
  	cumulative_acks += summary->nr_rot_new_acks;
  	if (cumulative_acks > 255)
  		cumulative_acks = 255;
  
  	summary->mode = call->cong_mode;
  	summary->cwnd = call->cong_cwnd;
  	summary->ssthresh = call->cong_ssthresh;
  	summary->cumulative_acks = cumulative_acks;
  	summary->dup_acks = call->cong_dup_acks;
  
  	switch (call->cong_mode) {
  	case RXRPC_CALL_SLOW_START:
  		if (summary->nr_nacks > 0)
  			goto packet_loss_detected;
  		if (summary->cumulative_acks > 0)
  			cwnd += 1;
  		if (cwnd >= call->cong_ssthresh) {
  			call->cong_mode = RXRPC_CALL_CONGEST_AVOIDANCE;
  			call->cong_tstamp = skb->tstamp;
  		}
  		goto out;
  
  	case RXRPC_CALL_CONGEST_AVOIDANCE:
  		if (summary->nr_nacks > 0)
  			goto packet_loss_detected;
  
  		/* We analyse the number of packets that get ACK'd per RTT
  		 * period and increase the window if we managed to fill it.
  		 */
  		if (call->peer->rtt_usage == 0)
  			goto out;
  		if (ktime_before(skb->tstamp,
  				 ktime_add_ns(call->cong_tstamp,
  					      call->peer->rtt)))
  			goto out_no_clear_ca;
  		change = rxrpc_cong_rtt_window_end;
  		call->cong_tstamp = skb->tstamp;
  		if (cumulative_acks >= cwnd)
  			cwnd++;
  		goto out;
  
  	case RXRPC_CALL_PACKET_LOSS:
  		if (summary->nr_nacks == 0)
  			goto resume_normality;
  
  		if (summary->new_low_nack) {
  			change = rxrpc_cong_new_low_nack;
  			call->cong_dup_acks = 1;
  			if (call->cong_extra > 1)
  				call->cong_extra = 1;
  			goto send_extra_data;
  		}
  
  		call->cong_dup_acks++;
  		if (call->cong_dup_acks < 3)
  			goto send_extra_data;
  
  		change = rxrpc_cong_begin_retransmission;
  		call->cong_mode = RXRPC_CALL_FAST_RETRANSMIT;
  		call->cong_ssthresh = max_t(unsigned int,
  					    summary->flight_size / 2, 2);
  		cwnd = call->cong_ssthresh + 3;
  		call->cong_extra = 0;
  		call->cong_dup_acks = 0;
  		resend = true;
  		goto out;
  
  	case RXRPC_CALL_FAST_RETRANSMIT:
  		if (!summary->new_low_nack) {
  			if (summary->nr_new_acks == 0)
  				cwnd += 1;
  			call->cong_dup_acks++;
  			if (call->cong_dup_acks == 2) {
  				change = rxrpc_cong_retransmit_again;
  				call->cong_dup_acks = 0;
  				resend = true;
  			}
  		} else {
  			change = rxrpc_cong_progress;
  			cwnd = call->cong_ssthresh;
  			if (summary->nr_nacks == 0)
  				goto resume_normality;
  		}
  		goto out;
  
  	default:
  		BUG();
  		goto out;
  	}
  
  resume_normality:
  	change = rxrpc_cong_cleared_nacks;
  	call->cong_dup_acks = 0;
  	call->cong_extra = 0;
  	call->cong_tstamp = skb->tstamp;
  	if (cwnd < call->cong_ssthresh)
  		call->cong_mode = RXRPC_CALL_SLOW_START;
  	else
  		call->cong_mode = RXRPC_CALL_CONGEST_AVOIDANCE;
  out:
  	cumulative_acks = 0;
  out_no_clear_ca:
  	if (cwnd >= RXRPC_RXTX_BUFF_SIZE - 1)
  		cwnd = RXRPC_RXTX_BUFF_SIZE - 1;
  	call->cong_cwnd = cwnd;
  	call->cong_cumul_acks = cumulative_acks;
  	trace_rxrpc_congest(call, summary, acked_serial, change);
  	if (resend && !test_and_set_bit(RXRPC_CALL_EV_RESEND, &call->events))
  		rxrpc_queue_call(call);
  	return;
  
  packet_loss_detected:
  	change = rxrpc_cong_saw_nack;
  	call->cong_mode = RXRPC_CALL_PACKET_LOSS;
  	call->cong_dup_acks = 0;
  	goto send_extra_data;
  
  send_extra_data:
  	/* Send some previously unsent DATA if we have some to advance the ACK
  	 * state.
  	 */
  	if (call->rxtx_annotations[call->tx_top & RXRPC_RXTX_BUFF_MASK] &
  	    RXRPC_TX_ANNO_LAST ||
  	    summary->nr_acks != call->tx_top - call->tx_hard_ack) {
  		call->cong_extra++;
  		wake_up(&call->waitq);
  	}
  	goto out_no_clear_ca;
  }
  
  /*
   * Ping the other end to fill our RTT cache and to retrieve the rwind
   * and MTU parameters.
   */
  static void rxrpc_send_ping(struct rxrpc_call *call, struct sk_buff *skb,
  			    int skew)
  {
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  	ktime_t now = skb->tstamp;
  
  	if (call->peer->rtt_usage < 3 ||
  	    ktime_before(ktime_add_ms(call->peer->rtt_last_req, 1000), now))
  		rxrpc_propose_ACK(call, RXRPC_ACK_PING, skew, sp->hdr.serial,
  				  true, true,
  				  rxrpc_propose_ack_ping_for_params);
  }
  
  /*
   * Apply a hard ACK by advancing the Tx window.
   */
  static void rxrpc_rotate_tx_window(struct rxrpc_call *call, rxrpc_seq_t to,
  				   struct rxrpc_ack_summary *summary)
  {
  	struct sk_buff *skb, *list = NULL;
  	int ix;
  	u8 annotation;
  
  	if (call->acks_lowest_nak == call->tx_hard_ack) {
  		call->acks_lowest_nak = to;
  	} else if (before_eq(call->acks_lowest_nak, to)) {
  		summary->new_low_nack = true;
  		call->acks_lowest_nak = to;
  	}
  
  	spin_lock(&call->lock);
  
  	while (before(call->tx_hard_ack, to)) {
  		call->tx_hard_ack++;
  		ix = call->tx_hard_ack & RXRPC_RXTX_BUFF_MASK;
  		skb = call->rxtx_buffer[ix];
  		annotation = call->rxtx_annotations[ix];
  		rxrpc_see_skb(skb, rxrpc_skb_tx_rotated);
  		call->rxtx_buffer[ix] = NULL;
  		call->rxtx_annotations[ix] = 0;
  		skb->next = list;
  		list = skb;
  
  		if (annotation & RXRPC_TX_ANNO_LAST)
  			set_bit(RXRPC_CALL_TX_LAST, &call->flags);
  		if ((annotation & RXRPC_TX_ANNO_MASK) != RXRPC_TX_ANNO_ACK)
  			summary->nr_rot_new_acks++;
  	}
  
  	spin_unlock(&call->lock);
  
  	trace_rxrpc_transmit(call, (test_bit(RXRPC_CALL_TX_LAST, &call->flags) ?
  				    rxrpc_transmit_rotate_last :
  				    rxrpc_transmit_rotate));
  	wake_up(&call->waitq);
  
  	while (list) {
  		skb = list;
  		list = skb->next;
  		skb->next = NULL;
  		rxrpc_free_skb(skb, rxrpc_skb_tx_freed);
  	}
  }
  
  /*
   * End the transmission phase of a call.
   *
   * This occurs when we get an ACKALL packet, the first DATA packet of a reply,
   * or a final ACK packet.
   */
  static bool rxrpc_end_tx_phase(struct rxrpc_call *call, bool reply_begun,
  			       const char *abort_why)
  {
  
  	ASSERT(test_bit(RXRPC_CALL_TX_LAST, &call->flags));
  
  	write_lock(&call->state_lock);
  
  	switch (call->state) {
  	case RXRPC_CALL_CLIENT_SEND_REQUEST:
  	case RXRPC_CALL_CLIENT_AWAIT_REPLY:
  		if (reply_begun)
  			call->state = RXRPC_CALL_CLIENT_RECV_REPLY;
  		else
  			call->state = RXRPC_CALL_CLIENT_AWAIT_REPLY;
  		break;
  
  	case RXRPC_CALL_SERVER_AWAIT_ACK:
  		__rxrpc_call_completed(call);
  		rxrpc_notify_socket(call);
  		break;
  
  	default:
  		goto bad_state;
  	}
  
  	write_unlock(&call->state_lock);
  	if (call->state == RXRPC_CALL_CLIENT_AWAIT_REPLY) {
  		rxrpc_propose_ACK(call, RXRPC_ACK_IDLE, 0, 0, false, true,
  				  rxrpc_propose_ack_client_tx_end);
  		trace_rxrpc_transmit(call, rxrpc_transmit_await_reply);
  	} else {
  		trace_rxrpc_transmit(call, rxrpc_transmit_end);
  	}
  	_leave(" = ok");
  	return true;
  
  bad_state:
  	write_unlock(&call->state_lock);
  	kdebug("end_tx %s", rxrpc_call_states[call->state]);
  	rxrpc_proto_abort(abort_why, call, call->tx_top);
  	return false;
  }
  
  /*
   * Begin the reply reception phase of a call.
   */
  static bool rxrpc_receiving_reply(struct rxrpc_call *call)
  {
  	struct rxrpc_ack_summary summary = { 0 };
  	rxrpc_seq_t top = READ_ONCE(call->tx_top);
  
  	if (call->ackr_reason) {
  		spin_lock_bh(&call->lock);
  		call->ackr_reason = 0;
  		call->resend_at = call->expire_at;
  		call->ack_at = call->expire_at;
  		spin_unlock_bh(&call->lock);
  		rxrpc_set_timer(call, rxrpc_timer_init_for_reply,
  				ktime_get_real());
  	}
  
  	if (!test_bit(RXRPC_CALL_TX_LAST, &call->flags))
  		rxrpc_rotate_tx_window(call, top, &summary);
  	if (!test_bit(RXRPC_CALL_TX_LAST, &call->flags)) {
  		rxrpc_proto_abort("TXL", call, top);
  		return false;
  	}
  	if (!rxrpc_end_tx_phase(call, true, "ETD"))
  		return false;
  	call->tx_phase = false;
  	return true;
  }
  
  /*
   * Scan a jumbo packet to validate its structure and to work out how many
   * subpackets it contains.
   *
   * A jumbo packet is a collection of consecutive packets glued together with
   * little headers between that indicate how to change the initial header for
   * each subpacket.
   *
   * RXRPC_JUMBO_PACKET must be set on all but the last subpacket - and all but
   * the last are RXRPC_JUMBO_DATALEN in size.  The last subpacket may be of any
   * size.
   */
  static bool rxrpc_validate_jumbo(struct sk_buff *skb)
  {
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  	unsigned int offset = sizeof(struct rxrpc_wire_header);
  	unsigned int len = skb->len;
  	int nr_jumbo = 1;
  	u8 flags = sp->hdr.flags;
  
  	do {
  		nr_jumbo++;
  		if (len - offset < RXRPC_JUMBO_SUBPKTLEN)
  			goto protocol_error;
  		if (flags & RXRPC_LAST_PACKET)
  			goto protocol_error;
  		offset += RXRPC_JUMBO_DATALEN;
  		if (skb_copy_bits(skb, offset, &flags, 1) < 0)
  			goto protocol_error;
  		offset += sizeof(struct rxrpc_jumbo_header);
  	} while (flags & RXRPC_JUMBO_PACKET);
  
  	sp->nr_jumbo = nr_jumbo;
  	return true;
  
  protocol_error:
  	return false;
  }
  
  /*
   * Handle reception of a duplicate packet.
   *
   * We have to take care to avoid an attack here whereby we're given a series of
   * jumbograms, each with a sequence number one before the preceding one and
   * filled up to maximum UDP size.  If they never send us the first packet in
   * the sequence, they can cause us to have to hold on to around 2MiB of kernel
   * space until the call times out.
   *
   * We limit the space usage by only accepting three duplicate jumbo packets per
   * call.  After that, we tell the other side we're no longer accepting jumbos
   * (that information is encoded in the ACK packet).
   */
  static void rxrpc_input_dup_data(struct rxrpc_call *call, rxrpc_seq_t seq,
  				 u8 annotation, bool *_jumbo_bad)
  {
  	/* Discard normal packets that are duplicates. */
  	if (annotation == 0)
  		return;
  
  	/* Skip jumbo subpackets that are duplicates.  When we've had three or
  	 * more partially duplicate jumbo packets, we refuse to take any more
  	 * jumbos for this call.
  	 */
  	if (!*_jumbo_bad) {
  		call->nr_jumbo_bad++;
  		*_jumbo_bad = true;
  	}
  }
  
  /*
   * Process a DATA packet, adding the packet to the Rx ring.
   */
  static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb,
  			     u16 skew)
  {
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  	unsigned int offset = sizeof(struct rxrpc_wire_header);
  	unsigned int ix;
  	rxrpc_serial_t serial = sp->hdr.serial, ack_serial = 0;
  	rxrpc_seq_t seq = sp->hdr.seq, hard_ack;
  	bool immediate_ack = false, jumbo_bad = false, queued;
  	u16 len;
  	u8 ack = 0, flags, annotation = 0;
  
  	_enter("{%u,%u},{%u,%u}",
  	       call->rx_hard_ack, call->rx_top, skb->len, seq);
  
  	_proto("Rx DATA %%%u { #%u f=%02x }",
  	       sp->hdr.serial, seq, sp->hdr.flags);
  
  	if (call->state >= RXRPC_CALL_COMPLETE)
  		return;
  
  	/* Received data implicitly ACKs all of the request packets we sent
  	 * when we're acting as a client.
  	 */
  	if ((call->state == RXRPC_CALL_CLIENT_SEND_REQUEST ||
  	     call->state == RXRPC_CALL_CLIENT_AWAIT_REPLY) &&
  	    !rxrpc_receiving_reply(call))
  		return;
  
  	call->ackr_prev_seq = seq;
  
  	hard_ack = READ_ONCE(call->rx_hard_ack);
  	if (after(seq, hard_ack + call->rx_winsize)) {
  		ack = RXRPC_ACK_EXCEEDS_WINDOW;
  		ack_serial = serial;
  		goto ack;
  	}
  
  	flags = sp->hdr.flags;
  	if (flags & RXRPC_JUMBO_PACKET) {
  		if (call->nr_jumbo_bad > 3) {
  			ack = RXRPC_ACK_NOSPACE;
  			ack_serial = serial;
  			goto ack;
  		}
  		annotation = 1;
  	}
  
  next_subpacket:
  	queued = false;
  	ix = seq & RXRPC_RXTX_BUFF_MASK;
  	len = skb->len;
  	if (flags & RXRPC_JUMBO_PACKET)
  		len = RXRPC_JUMBO_DATALEN;
  
  	if (flags & RXRPC_LAST_PACKET) {
  		if (test_bit(RXRPC_CALL_RX_LAST, &call->flags) &&
  		    seq != call->rx_top)
  			return rxrpc_proto_abort("LSN", call, seq);
  	} else {
  		if (test_bit(RXRPC_CALL_RX_LAST, &call->flags) &&
  		    after_eq(seq, call->rx_top))
  			return rxrpc_proto_abort("LSA", call, seq);
  	}
  
  	if (before_eq(seq, hard_ack)) {
  		ack = RXRPC_ACK_DUPLICATE;
  		ack_serial = serial;
  		goto skip;
  	}
  
  	if (flags & RXRPC_REQUEST_ACK && !ack) {
  		ack = RXRPC_ACK_REQUESTED;
  		ack_serial = serial;
  	}
  
  	if (call->rxtx_buffer[ix]) {
  		rxrpc_input_dup_data(call, seq, annotation, &jumbo_bad);
  		if (ack != RXRPC_ACK_DUPLICATE) {
  			ack = RXRPC_ACK_DUPLICATE;
  			ack_serial = serial;
  		}
  		immediate_ack = true;
  		goto skip;
  	}
  
  	/* Queue the packet.  We use a couple of memory barriers here as need
  	 * to make sure that rx_top is perceived to be set after the buffer
  	 * pointer and that the buffer pointer is set after the annotation and
  	 * the skb data.
  	 *
  	 * Barriers against rxrpc_recvmsg_data() and rxrpc_rotate_rx_window()
  	 * and also rxrpc_fill_out_ack().
  	 */
  	rxrpc_get_skb(skb, rxrpc_skb_rx_got);
  	call->rxtx_annotations[ix] = annotation;
  	smp_wmb();
  	call->rxtx_buffer[ix] = skb;
  	if (after(seq, call->rx_top)) {
  		smp_store_release(&call->rx_top, seq);
  	} else if (before(seq, call->rx_top)) {
  		/* Send an immediate ACK if we fill in a hole */
  		if (!ack) {
  			ack = RXRPC_ACK_DELAY;
  			ack_serial = serial;
  		}
  		immediate_ack = true;
  	}
  	if (flags & RXRPC_LAST_PACKET) {
  		set_bit(RXRPC_CALL_RX_LAST, &call->flags);
  		trace_rxrpc_receive(call, rxrpc_receive_queue_last, serial, seq);
  	} else {
  		trace_rxrpc_receive(call, rxrpc_receive_queue, serial, seq);
  	}
  	queued = true;
  
  	if (after_eq(seq, call->rx_expect_next)) {
  		if (after(seq, call->rx_expect_next)) {
  			_net("OOS %u > %u", seq, call->rx_expect_next);
  			ack = RXRPC_ACK_OUT_OF_SEQUENCE;
  			ack_serial = serial;
  		}
  		call->rx_expect_next = seq + 1;
  	}
  
  skip:
  	offset += len;
  	if (flags & RXRPC_JUMBO_PACKET) {
  		if (skb_copy_bits(skb, offset, &flags, 1) < 0)
  			return rxrpc_proto_abort("XJF", call, seq);
  		offset += sizeof(struct rxrpc_jumbo_header);
  		seq++;
  		serial++;
  		annotation++;
  		if (flags & RXRPC_JUMBO_PACKET)
  			annotation |= RXRPC_RX_ANNO_JLAST;
  		if (after(seq, hard_ack + call->rx_winsize)) {
  			ack = RXRPC_ACK_EXCEEDS_WINDOW;
  			ack_serial = serial;
  			if (!jumbo_bad) {
  				call->nr_jumbo_bad++;
  				jumbo_bad = true;
  			}
  			goto ack;
  		}
  
  		_proto("Rx DATA Jumbo %%%u", serial);
  		goto next_subpacket;
  	}
  
  	if (queued && flags & RXRPC_LAST_PACKET && !ack) {
  		ack = RXRPC_ACK_DELAY;
  		ack_serial = serial;
  	}
  
  ack:
  	if (ack)
  		rxrpc_propose_ACK(call, ack, skew, ack_serial,
  				  immediate_ack, true,
  				  rxrpc_propose_ack_input_data);
  
  	if (sp->hdr.seq == READ_ONCE(call->rx_hard_ack) + 1)
  		rxrpc_notify_socket(call);
  	_leave(" [queued]");
  }
  
  /*
   * Process a requested ACK.
   */
  static void rxrpc_input_requested_ack(struct rxrpc_call *call,
  				      ktime_t resp_time,
  				      rxrpc_serial_t orig_serial,
  				      rxrpc_serial_t ack_serial)
  {
  	struct rxrpc_skb_priv *sp;
  	struct sk_buff *skb;
  	ktime_t sent_at;
  	int ix;
  
  	for (ix = 0; ix < RXRPC_RXTX_BUFF_SIZE; ix++) {
  		skb = call->rxtx_buffer[ix];
  		if (!skb)
  			continue;
  
  		sp = rxrpc_skb(skb);
  		if (sp->hdr.serial != orig_serial)
  			continue;
  		smp_rmb();
  		sent_at = skb->tstamp;
  		goto found;
  	}
  	return;
  
  found:
  	rxrpc_peer_add_rtt(call, rxrpc_rtt_rx_requested_ack,
  			   orig_serial, ack_serial, sent_at, resp_time);
  }
  
  /*
   * Process a ping response.
   */
  static void rxrpc_input_ping_response(struct rxrpc_call *call,
  				      ktime_t resp_time,
  				      rxrpc_serial_t orig_serial,
  				      rxrpc_serial_t ack_serial)
  {
  	rxrpc_serial_t ping_serial;
  	ktime_t ping_time;
  
  	ping_time = call->ping_time;
  	smp_rmb();
  	ping_serial = call->ping_serial;
  
  	if (!test_bit(RXRPC_CALL_PINGING, &call->flags) ||
  	    before(orig_serial, ping_serial))
  		return;
  	clear_bit(RXRPC_CALL_PINGING, &call->flags);
  	if (after(orig_serial, ping_serial))
  		return;
  
  	rxrpc_peer_add_rtt(call, rxrpc_rtt_rx_ping_response,
  			   orig_serial, ack_serial, ping_time, resp_time);
  }
  
  /*
   * Process the extra information that may be appended to an ACK packet
   */
  static void rxrpc_input_ackinfo(struct rxrpc_call *call, struct sk_buff *skb,
  				struct rxrpc_ackinfo *ackinfo)
  {
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  	struct rxrpc_peer *peer;
  	unsigned int mtu;
  	u32 rwind = ntohl(ackinfo->rwind);
  
  	_proto("Rx ACK %%%u Info { rx=%u max=%u rwin=%u jm=%u }",
  	       sp->hdr.serial,
  	       ntohl(ackinfo->rxMTU), ntohl(ackinfo->maxMTU),
  	       rwind, ntohl(ackinfo->jumbo_max));
  
  	if (rwind > RXRPC_RXTX_BUFF_SIZE - 1)
  		rwind = RXRPC_RXTX_BUFF_SIZE - 1;
  	call->tx_winsize = rwind;
  	if (call->cong_ssthresh > rwind)
  		call->cong_ssthresh = rwind;
  
  	mtu = min(ntohl(ackinfo->rxMTU), ntohl(ackinfo->maxMTU));
  
  	peer = call->peer;
  	if (mtu < peer->maxdata) {
  		spin_lock_bh(&peer->lock);
  		peer->maxdata = mtu;
  		peer->mtu = mtu + peer->hdrsize;
  		spin_unlock_bh(&peer->lock);
  		_net("Net MTU %u (maxdata %u)", peer->mtu, peer->maxdata);
  	}
  }
  
  /*
   * Process individual soft ACKs.
   *
   * Each ACK in the array corresponds to one packet and can be either an ACK or
   * a NAK.  If we get find an explicitly NAK'd packet we resend immediately;
   * packets that lie beyond the end of the ACK list are scheduled for resend by
   * the timer on the basis that the peer might just not have processed them at
   * the time the ACK was sent.
   */
  static void rxrpc_input_soft_acks(struct rxrpc_call *call, u8 *acks,
  				  rxrpc_seq_t seq, int nr_acks,
  				  struct rxrpc_ack_summary *summary)
  {
  	int ix;
  	u8 annotation, anno_type;
  
  	for (; nr_acks > 0; nr_acks--, seq++) {
  		ix = seq & RXRPC_RXTX_BUFF_MASK;
  		annotation = call->rxtx_annotations[ix];
  		anno_type = annotation & RXRPC_TX_ANNO_MASK;
  		annotation &= ~RXRPC_TX_ANNO_MASK;
  		switch (*acks++) {
  		case RXRPC_ACK_TYPE_ACK:
  			summary->nr_acks++;
  			if (anno_type == RXRPC_TX_ANNO_ACK)
  				continue;
  			summary->nr_new_acks++;
  			call->rxtx_annotations[ix] =
  				RXRPC_TX_ANNO_ACK | annotation;
  			break;
  		case RXRPC_ACK_TYPE_NACK:
  			if (!summary->nr_nacks &&
  			    call->acks_lowest_nak != seq) {
  				call->acks_lowest_nak = seq;
  				summary->new_low_nack = true;
  			}
  			summary->nr_nacks++;
  			if (anno_type == RXRPC_TX_ANNO_NAK)
  				continue;
  			summary->nr_new_nacks++;
  			if (anno_type == RXRPC_TX_ANNO_RETRANS)
  				continue;
  			call->rxtx_annotations[ix] =
  				RXRPC_TX_ANNO_NAK | annotation;
  			break;
  		default:
  			return rxrpc_proto_abort("SFT", call, 0);
  		}
  	}
  }
  
  /*
   * Process an ACK packet.
   *
   * ack.firstPacket is the sequence number of the first soft-ACK'd/NAK'd packet
   * in the ACK array.  Anything before that is hard-ACK'd and may be discarded.
   *
   * A hard-ACK means that a packet has been processed and may be discarded; a
   * soft-ACK means that the packet may be discarded and retransmission
   * requested.  A phase is complete when all packets are hard-ACK'd.
   */
  static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb,
  			    u16 skew)
  {
  	struct rxrpc_ack_summary summary = { 0 };
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  	union {
  		struct rxrpc_ackpacket ack;
  		struct rxrpc_ackinfo info;
  		u8 acks[RXRPC_MAXACKS];
  	} buf;
  	rxrpc_serial_t acked_serial;
  	rxrpc_seq_t first_soft_ack, hard_ack;
  	int nr_acks, offset, ioffset;
  
  	_enter("");
  
  	offset = sizeof(struct rxrpc_wire_header);
  	if (skb_copy_bits(skb, offset, &buf.ack, sizeof(buf.ack)) < 0) {
  		_debug("extraction failure");
  		return rxrpc_proto_abort("XAK", call, 0);
  	}
  	offset += sizeof(buf.ack);
  
  	acked_serial = ntohl(buf.ack.serial);
  	first_soft_ack = ntohl(buf.ack.firstPacket);
  	hard_ack = first_soft_ack - 1;
  	nr_acks = buf.ack.nAcks;
  	summary.ack_reason = (buf.ack.reason < RXRPC_ACK__INVALID ?
  			      buf.ack.reason : RXRPC_ACK__INVALID);
  
  	trace_rxrpc_rx_ack(call, first_soft_ack, summary.ack_reason, nr_acks);
  
  	_proto("Rx ACK %%%u { m=%hu f=#%u p=#%u s=%%%u r=%s n=%u }",
  	       sp->hdr.serial,
  	       ntohs(buf.ack.maxSkew),
  	       first_soft_ack,
  	       ntohl(buf.ack.previousPacket),
  	       acked_serial,
  	       rxrpc_ack_names[summary.ack_reason],
  	       buf.ack.nAcks);
  
  	if (buf.ack.reason == RXRPC_ACK_PING_RESPONSE)
  		rxrpc_input_ping_response(call, skb->tstamp, acked_serial,
  					  sp->hdr.serial);
  	if (buf.ack.reason == RXRPC_ACK_REQUESTED)
  		rxrpc_input_requested_ack(call, skb->tstamp, acked_serial,
  					  sp->hdr.serial);
  
  	if (buf.ack.reason == RXRPC_ACK_PING) {
  		_proto("Rx ACK %%%u PING Request", sp->hdr.serial);
  		rxrpc_propose_ACK(call, RXRPC_ACK_PING_RESPONSE,
  				  skew, sp->hdr.serial, true, true,
  				  rxrpc_propose_ack_respond_to_ping);
  	} else if (sp->hdr.flags & RXRPC_REQUEST_ACK) {
  		rxrpc_propose_ACK(call, RXRPC_ACK_REQUESTED,
  				  skew, sp->hdr.serial, true, true,
  				  rxrpc_propose_ack_respond_to_ack);
  	}
  
  	ioffset = offset + nr_acks + 3;
  	if (skb->len >= ioffset + sizeof(buf.info)) {
  		if (skb_copy_bits(skb, ioffset, &buf.info, sizeof(buf.info)) < 0)
  			return rxrpc_proto_abort("XAI", call, 0);
  		rxrpc_input_ackinfo(call, skb, &buf.info);
  	}
  
  	if (first_soft_ack == 0)
  		return rxrpc_proto_abort("AK0", call, 0);
  
  	/* Ignore ACKs unless we are or have just been transmitting. */
  	switch (call->state) {
  	case RXRPC_CALL_CLIENT_SEND_REQUEST:
  	case RXRPC_CALL_CLIENT_AWAIT_REPLY:
  	case RXRPC_CALL_SERVER_SEND_REPLY:
  	case RXRPC_CALL_SERVER_AWAIT_ACK:
  		break;
  	default:
  		return;
  	}
  
  	/* Discard any out-of-order or duplicate ACKs. */
  	if (before_eq(sp->hdr.serial, call->acks_latest)) {
  		_debug("discard ACK %d <= %d",
  		       sp->hdr.serial, call->acks_latest);
  		return;
  	}
  	call->acks_latest_ts = skb->tstamp;
  	call->acks_latest = sp->hdr.serial;
  
  	if (before(hard_ack, call->tx_hard_ack) ||
  	    after(hard_ack, call->tx_top))
  		return rxrpc_proto_abort("AKW", call, 0);
  	if (nr_acks > call->tx_top - hard_ack)
  		return rxrpc_proto_abort("AKN", call, 0);
  
  	if (after(hard_ack, call->tx_hard_ack))
  		rxrpc_rotate_tx_window(call, hard_ack, &summary);
  
  	if (nr_acks > 0) {
  		if (skb_copy_bits(skb, offset, buf.acks, nr_acks) < 0)
  			return rxrpc_proto_abort("XSA", call, 0);
  		rxrpc_input_soft_acks(call, buf.acks, first_soft_ack, nr_acks,
  				      &summary);
  	}
  
  	if (test_bit(RXRPC_CALL_TX_LAST, &call->flags)) {
  		rxrpc_end_tx_phase(call, false, "ETA");
  		return;
  	}
  
  	if (call->rxtx_annotations[call->tx_top & RXRPC_RXTX_BUFF_MASK] &
  	    RXRPC_TX_ANNO_LAST &&
  	    summary.nr_acks == call->tx_top - hard_ack &&
  	    rxrpc_is_client_call(call))
  		rxrpc_propose_ACK(call, RXRPC_ACK_PING, skew, sp->hdr.serial,
  				  false, true,
  				  rxrpc_propose_ack_ping_for_lost_reply);
  
  	return rxrpc_congestion_management(call, skb, &summary, acked_serial);
  }
  
  /*
   * Process an ACKALL packet.
   */
  static void rxrpc_input_ackall(struct rxrpc_call *call, struct sk_buff *skb)
  {
  	struct rxrpc_ack_summary summary = { 0 };
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  
  	_proto("Rx ACKALL %%%u", sp->hdr.serial);
  
  	rxrpc_rotate_tx_window(call, call->tx_top, &summary);
  	if (test_bit(RXRPC_CALL_TX_LAST, &call->flags))
  		rxrpc_end_tx_phase(call, false, "ETL");
  }
  
  /*
   * Process an ABORT packet.
   */
  static void rxrpc_input_abort(struct rxrpc_call *call, struct sk_buff *skb)
  {
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  	__be32 wtmp;
  	u32 abort_code = RX_CALL_DEAD;
  
  	_enter("");
  
  	if (skb->len >= 4 &&
  	    skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
  			  &wtmp, sizeof(wtmp)) >= 0)
  		abort_code = ntohl(wtmp);
  
  	_proto("Rx ABORT %%%u { %x }", sp->hdr.serial, abort_code);
  
  	if (rxrpc_set_call_completion(call, RXRPC_CALL_REMOTELY_ABORTED,
  				      abort_code, ECONNABORTED))
  		rxrpc_notify_socket(call);
  }
  
  /*
   * Process an incoming call packet.
   */
  static void rxrpc_input_call_packet(struct rxrpc_call *call,
  				    struct sk_buff *skb, u16 skew)
  {
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  
  	_enter("%p,%p", call, skb);
  
  	switch (sp->hdr.type) {
  	case RXRPC_PACKET_TYPE_DATA:
  		rxrpc_input_data(call, skb, skew);
  		break;
  
  	case RXRPC_PACKET_TYPE_ACK:
  		rxrpc_input_ack(call, skb, skew);
  		break;
  
  	case RXRPC_PACKET_TYPE_BUSY:
  		_proto("Rx BUSY %%%u", sp->hdr.serial);
  
  		/* Just ignore BUSY packets from the server; the retry and
  		 * lifespan timers will take care of business.  BUSY packets
  		 * from the client don't make sense.
  		 */
  		break;
  
  	case RXRPC_PACKET_TYPE_ABORT:
  		rxrpc_input_abort(call, skb);
  		break;
  
  	case RXRPC_PACKET_TYPE_ACKALL:
  		rxrpc_input_ackall(call, skb);
  		break;
  
  	default:
  		_proto("Rx %s %%%u", rxrpc_pkts[sp->hdr.type], sp->hdr.serial);
  		break;
  	}
  
  	_leave("");
  }
  
  /*
   * Handle a new call on a channel implicitly completing the preceding call on
   * that channel.
   *
   * TODO: If callNumber > call_id + 1, renegotiate security.
   */
  static void rxrpc_input_implicit_end_call(struct rxrpc_connection *conn,
  					  struct rxrpc_call *call)
  {
  	switch (call->state) {
  	case RXRPC_CALL_SERVER_AWAIT_ACK:
  		rxrpc_call_completed(call);
  		break;
  	case RXRPC_CALL_COMPLETE:
  		break;
  	default:
  		if (rxrpc_abort_call("IMP", call, 0, RX_CALL_DEAD, ESHUTDOWN)) {
  			set_bit(RXRPC_CALL_EV_ABORT, &call->events);
  			rxrpc_queue_call(call);
  		}
  		break;
  	}
  
  	__rxrpc_disconnect_call(conn, call);
  	rxrpc_notify_socket(call);
  }
  
  /*
   * post connection-level events to the connection
   * - this includes challenges, responses, some aborts and call terminal packet
   *   retransmission.
   */
  static void rxrpc_post_packet_to_conn(struct rxrpc_connection *conn,
  				      struct sk_buff *skb)
  {
  	_enter("%p,%p", conn, skb);
  
  	skb_queue_tail(&conn->rx_queue, skb);
  	rxrpc_queue_conn(conn);
  }
  
  /*
   * post endpoint-level events to the local endpoint
   * - this includes debug and version messages
   */
  static void rxrpc_post_packet_to_local(struct rxrpc_local *local,
  				       struct sk_buff *skb)
  {
  	_enter("%p,%p", local, skb);
  
  	skb_queue_tail(&local->event_queue, skb);
  	rxrpc_queue_local(local);
  }
  
  /*
   * put a packet up for transport-level abort
   */
  static void rxrpc_reject_packet(struct rxrpc_local *local, struct sk_buff *skb)
  {
  	CHECK_SLAB_OKAY(&local->usage);
  
  	skb_queue_tail(&local->reject_queue, skb);
  	rxrpc_queue_local(local);
  }
  
  /*
   * Extract the wire header from a packet and translate the byte order.
   */
  static noinline
  int rxrpc_extract_header(struct rxrpc_skb_priv *sp, struct sk_buff *skb)
  {
  	struct rxrpc_wire_header whdr;
  
  	/* dig out the RxRPC connection details */
  	if (skb_copy_bits(skb, 0, &whdr, sizeof(whdr)) < 0)
  		return -EBADMSG;
  
  	memset(sp, 0, sizeof(*sp));
  	sp->hdr.epoch		= ntohl(whdr.epoch);
  	sp->hdr.cid		= ntohl(whdr.cid);
  	sp->hdr.callNumber	= ntohl(whdr.callNumber);
  	sp->hdr.seq		= ntohl(whdr.seq);
  	sp->hdr.serial		= ntohl(whdr.serial);
  	sp->hdr.flags		= whdr.flags;
  	sp->hdr.type		= whdr.type;
  	sp->hdr.userStatus	= whdr.userStatus;
  	sp->hdr.securityIndex	= whdr.securityIndex;
  	sp->hdr._rsvd		= ntohs(whdr._rsvd);
  	sp->hdr.serviceId	= ntohs(whdr.serviceId);
  	return 0;
  }
  
  /*
   * handle data received on the local endpoint
   * - may be called in interrupt context
   *
   * The socket is locked by the caller and this prevents the socket from being
   * shut down and the local endpoint from going away, thus sk_user_data will not
   * be cleared until this function returns.
   */
  void rxrpc_data_ready(struct sock *udp_sk)
  {
  	struct rxrpc_connection *conn;
  	struct rxrpc_channel *chan;
  	struct rxrpc_call *call;
  	struct rxrpc_skb_priv *sp;
  	struct rxrpc_local *local = udp_sk->sk_user_data;
  	struct sk_buff *skb;
  	unsigned int channel;
  	int ret, skew;
  
  	_enter("%p", udp_sk);
  
  	ASSERT(!irqs_disabled());
  
  	skb = skb_recv_datagram(udp_sk, 0, 1, &ret);
  	if (!skb) {
  		if (ret == -EAGAIN)
  			return;
  		_debug("UDP socket error %d", ret);
  		return;
  	}
  
  	rxrpc_new_skb(skb, rxrpc_skb_rx_received);
  
  	_net("recv skb %p", skb);
  
  	/* we'll probably need to checksum it (didn't call sock_recvmsg) */
  	if (skb_checksum_complete(skb)) {
  		rxrpc_free_skb(skb, rxrpc_skb_rx_freed);
  		__UDP_INC_STATS(&init_net, UDP_MIB_INERRORS, 0);
  		_leave(" [CSUM failed]");
  		return;
  	}
  
  	__UDP_INC_STATS(&init_net, UDP_MIB_INDATAGRAMS, 0);
  
  	/* The socket buffer we have is owned by UDP, with UDP's data all over
  	 * it, but we really want our own data there.
  	 */
  	skb_orphan(skb);
  	sp = rxrpc_skb(skb);
  
  	/* dig out the RxRPC connection details */
  	if (rxrpc_extract_header(sp, skb) < 0)
  		goto bad_message;
  
  	if (IS_ENABLED(CONFIG_AF_RXRPC_INJECT_LOSS)) {
  		static int lose;
  		if ((lose++ & 7) == 7) {
  			trace_rxrpc_rx_lose(sp);
  			rxrpc_lose_skb(skb, rxrpc_skb_rx_lost);
  			return;
  		}
  	}
  
  	trace_rxrpc_rx_packet(sp);
  
  	_net("Rx RxRPC %s ep=%x call=%x:%x",
  	     sp->hdr.flags & RXRPC_CLIENT_INITIATED ? "ToServer" : "ToClient",
  	     sp->hdr.epoch, sp->hdr.cid, sp->hdr.callNumber);
  
  	if (sp->hdr.type >= RXRPC_N_PACKET_TYPES ||
  	    !((RXRPC_SUPPORTED_PACKET_TYPES >> sp->hdr.type) & 1)) {
  		_proto("Rx Bad Packet Type %u", sp->hdr.type);
  		goto bad_message;
  	}
  
  	switch (sp->hdr.type) {
  	case RXRPC_PACKET_TYPE_VERSION:
  		rxrpc_post_packet_to_local(local, skb);
  		goto out;
  
  	case RXRPC_PACKET_TYPE_BUSY:
  		if (sp->hdr.flags & RXRPC_CLIENT_INITIATED)
  			goto discard;
  
  	case RXRPC_PACKET_TYPE_DATA:
  		if (sp->hdr.callNumber == 0)
  			goto bad_message;
  		if (sp->hdr.flags & RXRPC_JUMBO_PACKET &&
  		    !rxrpc_validate_jumbo(skb))
  			goto bad_message;
  		break;
  	}
  
  	rcu_read_lock();
  
  	conn = rxrpc_find_connection_rcu(local, skb);
  	if (conn) {
  		if (sp->hdr.securityIndex != conn->security_ix)
  			goto wrong_security;
  
  		if (sp->hdr.callNumber == 0) {
  			/* Connection-level packet */
  			_debug("CONN %p {%d}", conn, conn->debug_id);
  			rxrpc_post_packet_to_conn(conn, skb);
  			goto out_unlock;
  		}
  
  		/* Note the serial number skew here */
  		skew = (int)sp->hdr.serial - (int)conn->hi_serial;
  		if (skew >= 0) {
  			if (skew > 0)
  				conn->hi_serial = sp->hdr.serial;
  		} else {
  			skew = -skew;
  			skew = min(skew, 65535);
  		}
  
  		/* Call-bound packets are routed by connection channel. */
  		channel = sp->hdr.cid & RXRPC_CHANNELMASK;
  		chan = &conn->channels[channel];
  
  		/* Ignore really old calls */
  		if (sp->hdr.callNumber < chan->last_call)
  			goto discard_unlock;
  
  		if (sp->hdr.callNumber == chan->last_call) {
  			/* For the previous service call, if completed successfully, we
  			 * discard all further packets.
  			 */
  			if (rxrpc_conn_is_service(conn) &&
  			    (chan->last_type == RXRPC_PACKET_TYPE_ACK ||
  			     sp->hdr.type == RXRPC_PACKET_TYPE_ABORT))
  				goto discard_unlock;
  
  			/* But otherwise we need to retransmit the final packet from
  			 * data cached in the connection record.
  			 */
  			rxrpc_post_packet_to_conn(conn, skb);
  			goto out_unlock;
  		}
  
  		call = rcu_dereference(chan->call);
  
  		if (sp->hdr.callNumber > chan->call_id) {
  			if (!(sp->hdr.flags & RXRPC_CLIENT_INITIATED)) {
  				rcu_read_unlock();
  				goto reject_packet;
  			}
  			if (call)
  				rxrpc_input_implicit_end_call(conn, call);
  			call = NULL;
  		}
  	} else {
  		skew = 0;
  		call = NULL;
  	}
  
  	if (!call || atomic_read(&call->usage) == 0) {
  		if (!(sp->hdr.type & RXRPC_CLIENT_INITIATED) ||
  		    sp->hdr.callNumber == 0 ||
  		    sp->hdr.type != RXRPC_PACKET_TYPE_DATA)
  			goto bad_message_unlock;
  		if (sp->hdr.seq != 1)
  			goto discard_unlock;
  		call = rxrpc_new_incoming_call(local, conn, skb);
  		if (!call) {
  			rcu_read_unlock();
  			goto reject_packet;
  		}
  		rxrpc_send_ping(call, skb, skew);
  	}
  
  	rxrpc_input_call_packet(call, skb, skew);
  	goto discard_unlock;
  
  discard_unlock:
  	rcu_read_unlock();
  discard:
  	rxrpc_free_skb(skb, rxrpc_skb_rx_freed);
  out:
  	trace_rxrpc_rx_done(0, 0);
  	return;
  
  out_unlock:
  	rcu_read_unlock();
  	goto out;
  
  wrong_security:
  	rcu_read_unlock();
  	trace_rxrpc_abort("SEC", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
  			  RXKADINCONSISTENCY, EBADMSG);
  	skb->priority = RXKADINCONSISTENCY;
  	goto post_abort;
  
  bad_message_unlock:
  	rcu_read_unlock();
  bad_message:
  	trace_rxrpc_abort("BAD", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
  			  RX_PROTOCOL_ERROR, EBADMSG);
  	skb->priority = RX_PROTOCOL_ERROR;
  post_abort:
  	skb->mark = RXRPC_SKB_MARK_LOCAL_ABORT;
  reject_packet:
  	trace_rxrpc_rx_done(skb->mark, skb->priority);
  	rxrpc_reject_packet(local, skb);
  	_leave(" [badmsg]");
  }
  