net/rxrpc/conn_service.c

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