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 */
rxrpc_find_service_conn_rcu(struct rxrpc_peer * peer,struct sk_buff * skb)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 */
rxrpc_publish_service_conn(struct rxrpc_peer * peer,struct rxrpc_connection * conn)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 */
rxrpc_prealloc_service_connection(gfp_t gfp)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 */
rxrpc_new_incoming_connection(struct rxrpc_connection * conn,struct sk_buff * skb)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 */
rxrpc_unpublish_service_conn(struct rxrpc_connection * conn)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