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