rxrpc: Carry call state out of locked section in rxrpc_rotate_tx_window()

[mirror_ubuntu-bionic-kernel.git] / net / rxrpc / input.c

/* 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 bool rxrpc_rotate_tx_window(struct rxrpc_call *call, rxrpc_seq_t to,
                                   struct rxrpc_ack_summary *summary)
{
        struct sk_buff *skb, *list = NULL;
        bool rot_last = false;
        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);
                        rot_last = true;
                }
                if ((annotation & RXRPC_TX_ANNO_MASK) != RXRPC_TX_ANNO_ACK)
                        summary->nr_rot_new_acks++;
        }

        spin_unlock(&call->lock);

        trace_rxrpc_transmit(call, (rot_last ?
                                    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);
        }

        return rot_last;
}

/*
 * 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)
{
        unsigned int state;

        ASSERT(test_bit(RXRPC_CALL_TX_LAST, &call->flags));

        write_lock(&call->state_lock);

        state = call->state;
        switch (state) {
        case RXRPC_CALL_CLIENT_SEND_REQUEST:
        case RXRPC_CALL_CLIENT_AWAIT_REPLY:
                if (reply_begun)
                        call->state = state = RXRPC_CALL_CLIENT_RECV_REPLY;
                else
                        call->state = state = RXRPC_CALL_CLIENT_AWAIT_REPLY;
                break;

        case RXRPC_CALL_SERVER_AWAIT_ACK:
                __rxrpc_call_completed(call);
                rxrpc_notify_socket(call);
                state = call->state;
                break;

        default:
                goto bad_state;
        }

        write_unlock(&call->state_lock);
        if (state == RXRPC_CALL_CLIENT_AWAIT_REPLY)
                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 };
        unsigned long now, timo;
        rxrpc_seq_t top = READ_ONCE(call->tx_top);

        if (call->ackr_reason) {
                spin_lock_bh(&call->lock);
                call->ackr_reason = 0;
                spin_unlock_bh(&call->lock);
                now = jiffies;
                timo = now + MAX_JIFFY_OFFSET;
                WRITE_ONCE(call->resend_at, timo);
                WRITE_ONCE(call->ack_at, timo);
                trace_rxrpc_timer(call, rxrpc_timer_init_for_reply, now);
        }

        if (!test_bit(RXRPC_CALL_TX_LAST, &call->flags)) {
                if (!rxrpc_rotate_tx_window(call, top, &summary)) {
                        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);
        enum rxrpc_call_state state;
        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);

        state = READ_ONCE(call->state);
        if (state >= RXRPC_CALL_COMPLETE)
                return;

        if (call->state == RXRPC_CALL_SERVER_RECV_REQUEST) {
                unsigned long timo = READ_ONCE(call->next_req_timo);
                unsigned long now, expect_req_by;

                if (timo) {
                        now = jiffies;
                        expect_req_by = now + timo;
                        WRITE_ONCE(call->expect_req_by, expect_req_by);
                        rxrpc_reduce_call_timer(call, expect_req_by, now,
                                                rxrpc_timer_set_for_idle);
                }
        }

        /* Received data implicitly ACKs all of the request packets we sent
         * when we're acting as a client.
         */
        if ((state == RXRPC_CALL_CLIENT_SEND_REQUEST ||
             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);
        }

        trace_rxrpc_rx_data(call, seq, serial, flags, annotation);
        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 the response to a ping that we sent to find out if we lost an ACK.
 *
 * If we got back a ping response that indicates a lower tx_top than what we
 * had at the time of the ping transmission, we adjudge all the DATA packets
 * sent between the response tx_top and the ping-time tx_top to have been lost.
 */
static void rxrpc_input_check_for_lost_ack(struct rxrpc_call *call)
{
        rxrpc_seq_t top, bottom, seq;
        bool resend = false;

        spin_lock_bh(&call->lock);

        bottom = call->tx_hard_ack + 1;
        top = call->acks_lost_top;
        if (before(bottom, top)) {
                for (seq = bottom; before_eq(seq, top); seq++) {
                        int ix = seq & RXRPC_RXTX_BUFF_MASK;
                        u8 annotation = call->rxtx_annotations[ix];
                        u8 anno_type = annotation & RXRPC_TX_ANNO_MASK;

                        if (anno_type != RXRPC_TX_ANNO_UNACK)
                                continue;
                        annotation &= ~RXRPC_TX_ANNO_MASK;
                        annotation |= RXRPC_TX_ANNO_RETRANS;
                        call->rxtx_annotations[ix] = annotation;
                        resend = true;
                }
        }

        spin_unlock_bh(&call->lock);

        if (resend && !test_and_set_bit(RXRPC_CALL_EV_RESEND, &call->events))
                rxrpc_queue_call(call);
}

/*
 * 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 (orig_serial == call->acks_lost_ping)
                rxrpc_input_check_for_lost_ack(call);

        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;
        bool wake = false;
        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 (call->tx_winsize != rwind) {
                if (rwind > RXRPC_RXTX_BUFF_SIZE - 1)
                        rwind = RXRPC_RXTX_BUFF_SIZE - 1;
                if (rwind > call->tx_winsize)
                        wake = true;
                trace_rxrpc_rx_rwind_change(call, sp->hdr.serial,
                                            ntohl(ackinfo->rwind), wake);
                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);
        }

        if (wake)
                wake_up(&call->waitq);
}

/*
 * 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, sp->hdr.serial, acked_serial,
                           first_soft_ack, ntohl(buf.ack.previousPacket),
                           summary.ack_reason, nr_acks);

        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);
        }

        /* 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;

        /* Parse rwind and mtu sizes if provided. */
        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 (READ_ONCE(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;
        }

        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)) {
                if (rxrpc_rotate_tx_window(call, hard_ack, &summary)) {
                        rxrpc_end_tx_phase(call, false, "ETA");
                        return;
                }
        }

        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 (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);

        if (rxrpc_rotate_tx_window(call, call->tx_top, &summary))
                rxrpc_end_tx_phase(call, false, "ETL");
}

/*
 * Process an ABORT packet directed at a call.
 */
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);

        trace_rxrpc_rx_abort(call, sp->hdr.serial, abort_code);

        _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);
        unsigned long timo;

        _enter("%p,%p", call, skb);

        timo = READ_ONCE(call->next_rx_timo);
        if (timo) {
                unsigned long now = jiffies, expect_rx_by;

                expect_rx_by = now + timo;
                WRITE_ONCE(call->expect_rx_by, expect_rx_by);
                rxrpc_reduce_call_timer(call, expect_rx_by, now,
                                        rxrpc_timer_set_for_normal);
        }

        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:
                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 (READ_ONCE(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;
        }

        trace_rxrpc_improper_term(call);
        __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) {
                trace_rxrpc_rx_eproto(NULL, sp->hdr.serial,
                                      tracepoint_string("bad_hdr"));
                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_udp(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 UDP protocol already released all skb resources;
         * we are free to add our own data there.
         */
        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);

        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:
                if (rxrpc_to_client(sp))
                        goto discard;
                rxrpc_post_packet_to_local(local, skb);
                goto out;

        case RXRPC_PACKET_TYPE_BUSY:
                if (rxrpc_to_server(sp))
                        goto discard;
                /* Fall through */

        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.serviceId != conn->service_id) {
                        if (!test_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags) ||
                            conn->service_id != conn->params.service_id)
                                goto reupgrade;
                        conn->service_id = sp->hdr.serviceId;
                }

                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) {
                        if (chan->call ||
                            sp->hdr.type == RXRPC_PACKET_TYPE_ABORT)
                                goto discard_unlock;

                        /* 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)
                                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 (rxrpc_to_client(sp)) {
                                rcu_read_unlock();
                                goto reject_packet;
                        }
                        if (call)
                                rxrpc_input_implicit_end_call(conn, call);
                        call = NULL;
                }

                if (call && sp->hdr.serviceId != call->service_id)
                        call->service_id = sp->hdr.serviceId;
        } else {
                skew = 0;
                call = NULL;
        }

        if (!call || atomic_read(&call->usage) == 0) {
                if (rxrpc_to_client(sp) ||
                    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);
                mutex_unlock(&call->user_mutex);
        }

        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;

reupgrade:
        rcu_read_unlock();
        trace_rxrpc_abort("UPG", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
                          RX_PROTOCOL_ERROR, EBADMSG);
        goto protocol_error;

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);
protocol_error:
        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]");
}