linux/net/rxrpc/conn_service.c
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   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/* Service connection management
   3 *
   4 * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
   5 * Written by David Howells (dhowells@redhat.com)
   6 */
   7
   8#include <linux/slab.h>
   9#include "ar-internal.h"
  10
  11static struct rxrpc_bundle rxrpc_service_dummy_bundle = {
  12        .usage          = ATOMIC_INIT(1),
  13        .debug_id       = UINT_MAX,
  14        .channel_lock   = __SPIN_LOCK_UNLOCKED(&rxrpc_service_dummy_bundle.channel_lock),
  15};
  16
  17/*
  18 * Find a service connection under RCU conditions.
  19 *
  20 * We could use a hash table, but that is subject to bucket stuffing by an
  21 * attacker as the client gets to pick the epoch and cid values and would know
  22 * the hash function.  So, instead, we use a hash table for the peer and from
  23 * that an rbtree to find the service connection.  Under ordinary circumstances
  24 * it might be slower than a large hash table, but it is at least limited in
  25 * depth.
  26 */
  27struct rxrpc_connection *rxrpc_find_service_conn_rcu(struct rxrpc_peer *peer,
  28                                                     struct sk_buff *skb)
  29{
  30        struct rxrpc_connection *conn = NULL;
  31        struct rxrpc_conn_proto k;
  32        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
  33        struct rb_node *p;
  34        unsigned int seq = 0;
  35
  36        k.epoch = sp->hdr.epoch;
  37        k.cid   = sp->hdr.cid & RXRPC_CIDMASK;
  38
  39        do {
  40                /* Unfortunately, rbtree walking doesn't give reliable results
  41                 * under just the RCU read lock, so we have to check for
  42                 * changes.
  43                 */
  44                read_seqbegin_or_lock(&peer->service_conn_lock, &seq);
  45
  46                p = rcu_dereference_raw(peer->service_conns.rb_node);
  47                while (p) {
  48                        conn = rb_entry(p, struct rxrpc_connection, service_node);
  49
  50                        if (conn->proto.index_key < k.index_key)
  51                                p = rcu_dereference_raw(p->rb_left);
  52                        else if (conn->proto.index_key > k.index_key)
  53                                p = rcu_dereference_raw(p->rb_right);
  54                        else
  55                                break;
  56                        conn = NULL;
  57                }
  58        } while (need_seqretry(&peer->service_conn_lock, seq));
  59
  60        done_seqretry(&peer->service_conn_lock, seq);
  61        _leave(" = %d", conn ? conn->debug_id : -1);
  62        return conn;
  63}
  64
  65/*
  66 * Insert a service connection into a peer's tree, thereby making it a target
  67 * for incoming packets.
  68 */
  69static void rxrpc_publish_service_conn(struct rxrpc_peer *peer,
  70                                       struct rxrpc_connection *conn)
  71{
  72        struct rxrpc_connection *cursor = NULL;
  73        struct rxrpc_conn_proto k = conn->proto;
  74        struct rb_node **pp, *parent;
  75
  76        write_seqlock_bh(&peer->service_conn_lock);
  77
  78        pp = &peer->service_conns.rb_node;
  79        parent = NULL;
  80        while (*pp) {
  81                parent = *pp;
  82                cursor = rb_entry(parent,
  83                                  struct rxrpc_connection, service_node);
  84
  85                if (cursor->proto.index_key < k.index_key)
  86                        pp = &(*pp)->rb_left;
  87                else if (cursor->proto.index_key > k.index_key)
  88                        pp = &(*pp)->rb_right;
  89                else
  90                        goto found_extant_conn;
  91        }
  92
  93        rb_link_node_rcu(&conn->service_node, parent, pp);
  94        rb_insert_color(&conn->service_node, &peer->service_conns);
  95conn_published:
  96        set_bit(RXRPC_CONN_IN_SERVICE_CONNS, &conn->flags);
  97        write_sequnlock_bh(&peer->service_conn_lock);
  98        _leave(" = %d [new]", conn->debug_id);
  99        return;
 100
 101found_extant_conn:
 102        if (atomic_read(&cursor->usage) == 0)
 103                goto replace_old_connection;
 104        write_sequnlock_bh(&peer->service_conn_lock);
 105        /* We should not be able to get here.  rxrpc_incoming_connection() is
 106         * called in a non-reentrant context, so there can't be a race to
 107         * insert a new connection.
 108         */
 109        BUG();
 110
 111replace_old_connection:
 112        /* The old connection is from an outdated epoch. */
 113        _debug("replace conn");
 114        rb_replace_node_rcu(&cursor->service_node,
 115                            &conn->service_node,
 116                            &peer->service_conns);
 117        clear_bit(RXRPC_CONN_IN_SERVICE_CONNS, &cursor->flags);
 118        goto conn_published;
 119}
 120
 121/*
 122 * Preallocate a service connection.  The connection is placed on the proc and
 123 * reap lists so that we don't have to get the lock from BH context.
 124 */
 125struct rxrpc_connection *rxrpc_prealloc_service_connection(struct rxrpc_net *rxnet,
 126                                                           gfp_t gfp)
 127{
 128        struct rxrpc_connection *conn = rxrpc_alloc_connection(gfp);
 129
 130        if (conn) {
 131                /* We maintain an extra ref on the connection whilst it is on
 132                 * the rxrpc_connections list.
 133                 */
 134                conn->state = RXRPC_CONN_SERVICE_PREALLOC;
 135                atomic_set(&conn->usage, 2);
 136                conn->bundle = rxrpc_get_bundle(&rxrpc_service_dummy_bundle);
 137
 138                atomic_inc(&rxnet->nr_conns);
 139                write_lock(&rxnet->conn_lock);
 140                list_add_tail(&conn->link, &rxnet->service_conns);
 141                list_add_tail(&conn->proc_link, &rxnet->conn_proc_list);
 142                write_unlock(&rxnet->conn_lock);
 143
 144                trace_rxrpc_conn(conn->debug_id, rxrpc_conn_new_service,
 145                                 atomic_read(&conn->usage),
 146                                 __builtin_return_address(0));
 147        }
 148
 149        return conn;
 150}
 151
 152/*
 153 * Set up an incoming connection.  This is called in BH context with the RCU
 154 * read lock held.
 155 */
 156void rxrpc_new_incoming_connection(struct rxrpc_sock *rx,
 157                                   struct rxrpc_connection *conn,
 158                                   const struct rxrpc_security *sec,
 159                                   struct sk_buff *skb)
 160{
 161        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 162
 163        _enter("");
 164
 165        conn->proto.epoch       = sp->hdr.epoch;
 166        conn->proto.cid         = sp->hdr.cid & RXRPC_CIDMASK;
 167        conn->params.service_id = sp->hdr.serviceId;
 168        conn->service_id        = sp->hdr.serviceId;
 169        conn->security_ix       = sp->hdr.securityIndex;
 170        conn->out_clientflag    = 0;
 171        conn->security          = sec;
 172        if (conn->security_ix)
 173                conn->state     = RXRPC_CONN_SERVICE_UNSECURED;
 174        else
 175                conn->state     = RXRPC_CONN_SERVICE;
 176
 177        /* See if we should upgrade the service.  This can only happen on the
 178         * first packet on a new connection.  Once done, it applies to all
 179         * subsequent calls on that connection.
 180         */
 181        if (sp->hdr.userStatus == RXRPC_USERSTATUS_SERVICE_UPGRADE &&
 182            conn->service_id == rx->service_upgrade.from)
 183                conn->service_id = rx->service_upgrade.to;
 184
 185        /* Make the connection a target for incoming packets. */
 186        rxrpc_publish_service_conn(conn->params.peer, conn);
 187
 188        _net("CONNECTION new %d {%x}", conn->debug_id, conn->proto.cid);
 189}
 190
 191/*
 192 * Remove the service connection from the peer's tree, thereby removing it as a
 193 * target for incoming packets.
 194 */
 195void rxrpc_unpublish_service_conn(struct rxrpc_connection *conn)
 196{
 197        struct rxrpc_peer *peer = conn->params.peer;
 198
 199        write_seqlock_bh(&peer->service_conn_lock);
 200        if (test_and_clear_bit(RXRPC_CONN_IN_SERVICE_CONNS, &conn->flags))
 201                rb_erase(&conn->service_node, &peer->service_conns);
 202        write_sequnlock_bh(&peer->service_conn_lock);
 203}
 204