/* incoming call handling
 *
 * Copyright (C) 2007 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 <linux/circ_buf.h>
#include <net/sock.h>
#include <net/af_rxrpc.h>
#include <net/ip.h>
#include "ar-internal.h"

/*
 * Preallocate a single service call, connection and peer and, if possible,
 * give them a user ID and attach the user's side of the ID to them.
 */
static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
                                      struct rxrpc_backlog *b,
                                      rxrpc_notify_rx_t notify_rx,
                                      rxrpc_user_attach_call_t user_attach_call,
                                      unsigned long user_call_ID, gfp_t gfp)
{
        const void *here = __builtin_return_address(0);
        struct rxrpc_call *call;
        struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
        int max, tmp;
        unsigned int size = RXRPC_BACKLOG_MAX;
        unsigned int head, tail, call_head, call_tail;

        max = rx->sk.sk_max_ack_backlog;
        tmp = rx->sk.sk_ack_backlog;
        if (tmp >= max) {
                _leave(" = -ENOBUFS [full %u]", max);
                return -ENOBUFS;
        }
        max -= tmp;

        /* We don't need more conns and peers than we have calls, but on the
         * other hand, we shouldn't ever use more peers than conns or conns
         * than calls.
         */
        call_head = b->call_backlog_head;
        call_tail = READ_ONCE(b->call_backlog_tail);
        tmp = CIRC_CNT(call_head, call_tail, size);
        if (tmp >= max) {
                _leave(" = -ENOBUFS [enough %u]", tmp);
                return -ENOBUFS;
        }
        max = tmp + 1;

        head = b->peer_backlog_head;
        tail = READ_ONCE(b->peer_backlog_tail);
        if (CIRC_CNT(head, tail, size) < max) {
                struct rxrpc_peer *peer = rxrpc_alloc_peer(rx->local, gfp);
                if (!peer)
                        return -ENOMEM;
                b->peer_backlog[head] = peer;
                smp_store_release(&b->peer_backlog_head,
                                  (head + 1) & (size - 1));
        }

        head = b->conn_backlog_head;
        tail = READ_ONCE(b->conn_backlog_tail);
        if (CIRC_CNT(head, tail, size) < max) {
                struct rxrpc_connection *conn;

                conn = rxrpc_prealloc_service_connection(rxnet, gfp);
                if (!conn)
                        return -ENOMEM;
                b->conn_backlog[head] = conn;
                smp_store_release(&b->conn_backlog_head,
                                  (head + 1) & (size - 1));

                trace_rxrpc_conn(conn, rxrpc_conn_new_service,
                                 atomic_read(&conn->usage), here);
        }

        /* Now it gets complicated, because calls get registered with the
         * socket here, particularly if a user ID is preassigned by the user.
         */
        call = rxrpc_alloc_call(gfp);
        if (!call)
                return -ENOMEM;
        call->flags |= (1 << RXRPC_CALL_IS_SERVICE);
        call->state = RXRPC_CALL_SERVER_PREALLOC;

        trace_rxrpc_call(call, rxrpc_call_new_service,
                         atomic_read(&call->usage),
                         here, (const void *)user_call_ID);

        write_lock(&rx->call_lock);
        if (user_attach_call) {
                struct rxrpc_call *xcall;
                struct rb_node *parent, **pp;

                /* Check the user ID isn't already in use */
                pp = &rx->calls.rb_node;
                parent = NULL;
                while (*pp) {
                        parent = *pp;
                        xcall = rb_entry(parent, struct rxrpc_call, sock_node);
                        if (user_call_ID < call->user_call_ID)
                                pp = &(*pp)->rb_left;
                        else if (user_call_ID > call->user_call_ID)
                                pp = &(*pp)->rb_right;
                        else
                                goto id_in_use;
                }

                call->user_call_ID = user_call_ID;
                call->notify_rx = notify_rx;
                rxrpc_get_call(call, rxrpc_call_got_kernel);
                user_attach_call(call, user_call_ID);
                rxrpc_get_call(call, rxrpc_call_got_userid);
                rb_link_node(&call->sock_node, parent, pp);
                rb_insert_color(&call->sock_node, &rx->calls);
                set_bit(RXRPC_CALL_HAS_USERID, &call->flags);
        }

        list_add(&call->sock_link, &rx->sock_calls);

        write_unlock(&rx->call_lock);

        write_lock(&rxnet->call_lock);
        list_add_tail(&call->link, &rxnet->calls);
        write_unlock(&rxnet->call_lock);

        b->call_backlog[call_head] = call;
        smp_store_release(&b->call_backlog_head, (call_head + 1) & (size - 1));
        _leave(" = 0 [%d -> %lx]", call->debug_id, user_call_ID);
        return 0;

id_in_use:
        write_unlock(&rx->call_lock);
        rxrpc_cleanup_call(call);
        _leave(" = -EBADSLT");
        return -EBADSLT;
}

/*
 * Preallocate sufficient service connections, calls and peers to cover the
 * entire backlog of a socket.  When a new call comes in, if we don't have
 * sufficient of each available, the call gets rejected as busy or ignored.
 *
 * The backlog is replenished when a connection is accepted or rejected.
 */
int rxrpc_service_prealloc(struct rxrpc_sock *rx, gfp_t gfp)
{
        struct rxrpc_backlog *b = rx->backlog;

        if (!b) {
                b = kzalloc(sizeof(struct rxrpc_backlog), gfp);
                if (!b)
                        return -ENOMEM;
                rx->backlog = b;
        }

        if (rx->discard_new_call)
                return 0;

        while (rxrpc_service_prealloc_one(rx, b, NULL, NULL, 0, gfp) == 0)
                ;

        return 0;
}

/*
 * Discard the preallocation on a service.
 */
void rxrpc_discard_prealloc(struct rxrpc_sock *rx)
{
        struct rxrpc_backlog *b = rx->backlog;
        struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
        unsigned int size = RXRPC_BACKLOG_MAX, head, tail;

        if (!b)
                return;
        rx->backlog = NULL;

        /* Make sure that there aren't any incoming calls in progress before we
         * clear the preallocation buffers.
         */
        spin_lock_bh(&rx->incoming_lock);
        spin_unlock_bh(&rx->incoming_lock);

        head = b->peer_backlog_head;
        tail = b->peer_backlog_tail;
        while (CIRC_CNT(head, tail, size) > 0) {
                struct rxrpc_peer *peer = b->peer_backlog[tail];
                kfree(peer);
                tail = (tail + 1) & (size - 1);
        }

        head = b->conn_backlog_head;
        tail = b->conn_backlog_tail;
        while (CIRC_CNT(head, tail, size) > 0) {
                struct rxrpc_connection *conn = b->conn_backlog[tail];
                write_lock(&rxnet->conn_lock);
                list_del(&conn->link);
                list_del(&conn->proc_link);
                write_unlock(&rxnet->conn_lock);
                kfree(conn);
                tail = (tail + 1) & (size - 1);
        }

        head = b->call_backlog_head;
        tail = b->call_backlog_tail;
        while (CIRC_CNT(head, tail, size) > 0) {
                struct rxrpc_call *call = b->call_backlog[tail];
                call->socket = rx;
                if (rx->discard_new_call) {
                        _debug("discard %lx", call->user_call_ID);
                        rx->discard_new_call(call, call->user_call_ID);
                        rxrpc_put_call(call, rxrpc_call_put_kernel);
                }
                rxrpc_call_completed(call);
                rxrpc_release_call(rx, call);
                rxrpc_put_call(call, rxrpc_call_put);
                tail = (tail + 1) & (size - 1);
        }

        kfree(b);
}

/*
 * Allocate a new incoming call from the prealloc pool, along with a connection
 * and a peer as necessary.
 */
static struct rxrpc_call *rxrpc_alloc_incoming_call(struct rxrpc_sock *rx,
                                                    struct rxrpc_local *local,
                                                    struct rxrpc_connection *conn,
                                                    struct sk_buff *skb)
{
        struct rxrpc_backlog *b = rx->backlog;
        struct rxrpc_peer *peer, *xpeer;
        struct rxrpc_call *call;
        unsigned short call_head, conn_head, peer_head;
        unsigned short call_tail, conn_tail, peer_tail;
        unsigned short call_count, conn_count;

        /* #calls >= #conns >= #peers must hold true. */
        call_head = smp_load_acquire(&b->call_backlog_head);
        call_tail = b->call_backlog_tail;
        call_count = CIRC_CNT(call_head, call_tail, RXRPC_BACKLOG_MAX);
        conn_head = smp_load_acquire(&b->conn_backlog_head);
        conn_tail = b->conn_backlog_tail;
        conn_count = CIRC_CNT(conn_head, conn_tail, RXRPC_BACKLOG_MAX);
        ASSERTCMP(conn_count, >=, call_count);
        peer_head = smp_load_acquire(&b->peer_backlog_head);
        peer_tail = b->peer_backlog_tail;
        ASSERTCMP(CIRC_CNT(peer_head, peer_tail, RXRPC_BACKLOG_MAX), >=,
                  conn_count);

        if (call_count == 0)
                return NULL;

        if (!conn) {
                /* No connection.  We're going to need a peer to start off
                 * with.  If one doesn't yet exist, use a spare from the
                 * preallocation set.  We dump the address into the spare in
                 * anticipation - and to save on stack space.
                 */
                xpeer = b->peer_backlog[peer_tail];
                if (rxrpc_extract_addr_from_skb(local, &xpeer->srx, skb) < 0)
                        return NULL;

                peer = rxrpc_lookup_incoming_peer(local, xpeer);
                if (peer == xpeer) {
                        b->peer_backlog[peer_tail] = NULL;
                        smp_store_release(&b->peer_backlog_tail,
                                          (peer_tail + 1) &
                                          (RXRPC_BACKLOG_MAX - 1));
                }

                /* Now allocate and set up the connection */
                conn = b->conn_backlog[conn_tail];
                b->conn_backlog[conn_tail] = NULL;
                smp_store_release(&b->conn_backlog_tail,
                                  (conn_tail + 1) & (RXRPC_BACKLOG_MAX - 1));
                rxrpc_get_local(local);
                conn->params.local = local;
                conn->params.peer = peer;
                rxrpc_see_connection(conn);
                rxrpc_new_incoming_connection(rx, conn, skb);
        } else {
                rxrpc_get_connection(conn);
        }

        /* And now we can allocate and set up a new call */
        call = b->call_backlog[call_tail];
        b->call_backlog[call_tail] = NULL;
        smp_store_release(&b->call_backlog_tail,
                          (call_tail + 1) & (RXRPC_BACKLOG_MAX - 1));

        rxrpc_see_call(call);
        call->conn = conn;
        call->peer = rxrpc_get_peer(conn->params.peer);
        call->cong_cwnd = call->peer->cong_cwnd;
        return call;
}

/*
 * Set up a new incoming call.  Called in BH context with the RCU read lock
 * held.
 *
 * If this is for a kernel service, when we allocate the call, it will have
 * three refs on it: (1) the kernel service, (2) the user_call_ID tree, (3) the
 * retainer ref obtained from the backlog buffer.  Prealloc calls for userspace
 * services only have the ref from the backlog buffer.  We want to pass this
 * ref to non-BH context to dispose of.
 *
 * If we want to report an error, we mark the skb with the packet type and
 * abort code and return NULL.
 *
 * The call is returned with the user access mutex held.
 */
struct rxrpc_call *rxrpc_new_incoming_call(struct rxrpc_local *local,
                                           struct rxrpc_connection *conn,
                                           struct sk_buff *skb)
{
        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
        struct rxrpc_sock *rx;
        struct rxrpc_call *call;
        u16 service_id = sp->hdr.serviceId;

        _enter("");

        /* Get the socket providing the service */
        rx = rcu_dereference(local->service);
        if (rx && (service_id == rx->srx.srx_service ||
                   service_id == rx->second_service))
                goto found_service;

        trace_rxrpc_abort("INV", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,
                          RX_INVALID_OPERATION, EOPNOTSUPP);
        skb->mark = RXRPC_SKB_MARK_LOCAL_ABORT;
        skb->priority = RX_INVALID_OPERATION;
        _leave(" = NULL [service]");
        return NULL;

found_service:
        spin_lock(&rx->incoming_lock);
        if (rx->sk.sk_state == RXRPC_SERVER_LISTEN_DISABLED ||
            rx->sk.sk_state == RXRPC_CLOSE) {
                trace_rxrpc_abort("CLS", sp->hdr.cid, sp->hdr.callNumber,
                                  sp->hdr.seq, RX_INVALID_OPERATION, ESHUTDOWN);
                skb->mark = RXRPC_SKB_MARK_LOCAL_ABORT;
                skb->priority = RX_INVALID_OPERATION;
                _leave(" = NULL [close]");
                call = NULL;
                goto out;
        }

        call = rxrpc_alloc_incoming_call(rx, local, conn, skb);
        if (!call) {
                skb->mark = RXRPC_SKB_MARK_BUSY;
                _leave(" = NULL [busy]");
                call = NULL;
                goto out;
        }

        trace_rxrpc_receive(call, rxrpc_receive_incoming,
                            sp->hdr.serial, sp->hdr.seq);

        /* Lock the call to prevent rxrpc_kernel_send/recv_data() and
         * sendmsg()/recvmsg() inconveniently stealing the mutex once the
         * notification is generated.
         *
         * The BUG should never happen because the kernel should be well
         * behaved enough not to access the call before the first notification
         * event and userspace is prevented from doing so until the state is
         * appropriate.
         */
        if (!mutex_trylock(&call->user_mutex))
                BUG();

        /* Make the call live. */
        rxrpc_incoming_call(rx, call, skb);
        conn = call->conn;

        if (rx->notify_new_call)
                rx->notify_new_call(&rx->sk, call, call->user_call_ID);
        else
                sk_acceptq_added(&rx->sk);

        spin_lock(&conn->state_lock);
        switch (conn->state) {
        case RXRPC_CONN_SERVICE_UNSECURED:
                conn->state = RXRPC_CONN_SERVICE_CHALLENGING;
                set_bit(RXRPC_CONN_EV_CHALLENGE, &call->conn->events);
                rxrpc_queue_conn(call->conn);
                break;

        case RXRPC_CONN_SERVICE:
                write_lock(&call->state_lock);
                if (rx->discard_new_call)
                        call->state = RXRPC_CALL_SERVER_RECV_REQUEST;
                else
                        call->state = RXRPC_CALL_SERVER_ACCEPTING;
                write_unlock(&call->state_lock);
                break;

        case RXRPC_CONN_REMOTELY_ABORTED:
                rxrpc_set_call_completion(call, RXRPC_CALL_REMOTELY_ABORTED,
                                          conn->remote_abort, -ECONNABORTED);
                break;
        case RXRPC_CONN_LOCALLY_ABORTED:
                rxrpc_abort_call("CON", call, sp->hdr.seq,
                                 conn->local_abort, -ECONNABORTED);
                break;
        default:
                BUG();
        }
        spin_unlock(&conn->state_lock);

        if (call->state == RXRPC_CALL_SERVER_ACCEPTING)
                rxrpc_notify_socket(call);

        /* We have to discard the prealloc queue's ref here and rely on a
         * combination of the RCU read lock and refs held either by the socket
         * (recvmsg queue, to-be-accepted queue or user ID tree) or the kernel
         * service to prevent the call from being deallocated too early.
         */
        rxrpc_put_call(call, rxrpc_call_put);

        _leave(" = %p{%d}", call, call->debug_id);
out:
        spin_unlock(&rx->incoming_lock);
        return call;
}

/*
 * handle acceptance of a call by userspace
 * - assign the user call ID to the call at the front of the queue
 * - called with the socket locked.
 */
struct rxrpc_call *rxrpc_accept_call(struct rxrpc_sock *rx,
                                     unsigned long user_call_ID,
                                     rxrpc_notify_rx_t notify_rx)
        __releases(&rx->sk.sk_lock.slock)
{
        struct rxrpc_call *call;
        struct rb_node *parent, **pp;
        int ret;

        _enter(",%lx", user_call_ID);

        ASSERT(!irqs_disabled());

        write_lock(&rx->call_lock);

        if (list_empty(&rx->to_be_accepted)) {
                write_unlock(&rx->call_lock);
                release_sock(&rx->sk);
                kleave(" = -ENODATA [empty]");
                return ERR_PTR(-ENODATA);
        }

        /* check the user ID isn't already in use */
        pp = &rx->calls.rb_node;
        parent = NULL;
        while (*pp) {
                parent = *pp;
                call = rb_entry(parent, struct rxrpc_call, sock_node);

                if (user_call_ID < call->user_call_ID)
                        pp = &(*pp)->rb_left;
                else if (user_call_ID > call->user_call_ID)
                        pp = &(*pp)->rb_right;
                else
                        goto id_in_use;
        }

        /* Dequeue the first call and check it's still valid.  We gain
         * responsibility for the queue's reference.
         */
        call = list_entry(rx->to_be_accepted.next,
                          struct rxrpc_call, accept_link);
        write_unlock(&rx->call_lock);

        /* We need to gain the mutex from the interrupt handler without
         * upsetting lockdep, so we have to release it there and take it here.
         * We are, however, still holding the socket lock, so other accepts
         * must wait for us and no one can add the user ID behind our backs.
         */
        if (mutex_lock_interruptible(&call->user_mutex) < 0) {
                release_sock(&rx->sk);
                kleave(" = -ERESTARTSYS");
                return ERR_PTR(-ERESTARTSYS);
        }

        write_lock(&rx->call_lock);
        list_del_init(&call->accept_link);
        sk_acceptq_removed(&rx->sk);
        rxrpc_see_call(call);

        /* Find the user ID insertion point. */
        pp = &rx->calls.rb_node;
        parent = NULL;
        while (*pp) {
                parent = *pp;
                call = rb_entry(parent, struct rxrpc_call, sock_node);

                if (user_call_ID < call->user_call_ID)
                        pp = &(*pp)->rb_left;
                else if (user_call_ID > call->user_call_ID)
                        pp = &(*pp)->rb_right;
                else
                        BUG();
        }

        write_lock_bh(&call->state_lock);
        switch (call->state) {
        case RXRPC_CALL_SERVER_ACCEPTING:
                call->state = RXRPC_CALL_SERVER_RECV_REQUEST;
                break;
        case RXRPC_CALL_COMPLETE:
                ret = call->error;
                goto out_release;
        default:
                BUG();
        }

        /* formalise the acceptance */
        call->notify_rx = notify_rx;
        call->user_call_ID = user_call_ID;
        rxrpc_get_call(call, rxrpc_call_got_userid);
        rb_link_node(&call->sock_node, parent, pp);
        rb_insert_color(&call->sock_node, &rx->calls);
        if (test_and_set_bit(RXRPC_CALL_HAS_USERID, &call->flags))
                BUG();

        write_unlock_bh(&call->state_lock);
        write_unlock(&rx->call_lock);
        rxrpc_notify_socket(call);
        rxrpc_service_prealloc(rx, GFP_KERNEL);
        release_sock(&rx->sk);
        _leave(" = %p{%d}", call, call->debug_id);
        return call;

out_release:
        _debug("release %p", call);
        write_unlock_bh(&call->state_lock);
        write_unlock(&rx->call_lock);
        rxrpc_release_call(rx, call);
        rxrpc_put_call(call, rxrpc_call_put);
        goto out;

id_in_use:
        ret = -EBADSLT;
        write_unlock(&rx->call_lock);
out:
        rxrpc_service_prealloc(rx, GFP_KERNEL);
        release_sock(&rx->sk);
        _leave(" = %d", ret);
        return ERR_PTR(ret);
}

/*
 * Handle rejection of a call by userspace
 * - reject the call at the front of the queue
 */
int rxrpc_reject_call(struct rxrpc_sock *rx)
{
        struct rxrpc_call *call;
        bool abort = false;
        int ret;

        _enter("");

        ASSERT(!irqs_disabled());

        write_lock(&rx->call_lock);

        if (list_empty(&rx->to_be_accepted)) {
                write_unlock(&rx->call_lock);
                return -ENODATA;
        }

        /* Dequeue the first call and check it's still valid.  We gain
         * responsibility for the queue's reference.
         */
        call = list_entry(rx->to_be_accepted.next,
                          struct rxrpc_call, accept_link);
        list_del_init(&call->accept_link);
        sk_acceptq_removed(&rx->sk);
        rxrpc_see_call(call);

        write_lock_bh(&call->state_lock);
        switch (call->state) {
        case RXRPC_CALL_SERVER_ACCEPTING:
                __rxrpc_abort_call("REJ", call, 1, RX_USER_ABORT, -ECONNABORTED);
                abort = true;
                /* fall through */
        case RXRPC_CALL_COMPLETE:
                ret = call->error;
                goto out_discard;
        default:
                BUG();
        }

out_discard:
        write_unlock_bh(&call->state_lock);
        write_unlock(&rx->call_lock);
        if (abort) {
                rxrpc_send_abort_packet(call);
                rxrpc_release_call(rx, call);
                rxrpc_put_call(call, rxrpc_call_put);
        }
        rxrpc_service_prealloc(rx, GFP_KERNEL);
        _leave(" = %d", ret);
        return ret;
}

/*
 * rxrpc_kernel_charge_accept - Charge up socket with preallocated calls
 * @sock: The socket on which to preallocate
 * @notify_rx: Event notification function for the call
 * @user_attach_call: Func to attach call to user_call_ID
 * @user_call_ID: The tag to attach to the preallocated call
 * @gfp: The allocation conditions.
 *
 * Charge up the socket with preallocated calls, each with a user ID.  A
 * function should be provided to effect the attachment from the user's side.
 * The user is given a ref to hold on the call.
 *
 * Note that the call may be come connected before this function returns.
 */
int rxrpc_kernel_charge_accept(struct socket *sock,
                               rxrpc_notify_rx_t notify_rx,
                               rxrpc_user_attach_call_t user_attach_call,
                               unsigned long user_call_ID, gfp_t gfp)
{
        struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
        struct rxrpc_backlog *b = rx->backlog;

        if (sock->sk->sk_state == RXRPC_CLOSE)
                return -ESHUTDOWN;

        return rxrpc_service_prealloc_one(rx, b, notify_rx,
                                          user_attach_call, user_call_ID,
                                          gfp);
}
EXPORT_SYMBOL(rxrpc_kernel_charge_accept);