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 */
21struct 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(lock: &peer->service_conn_lock, seq: &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(lock: &peer->service_conn_lock, seq));
53
54 done_seqretry(lock: &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 */
63static 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(sl: &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(node: &conn->service_node, parent, rb_link: pp);
88 rb_insert_color(&conn->service_node, &peer->service_conns);
89conn_published:
90 set_bit(nr: RXRPC_CONN_IN_SERVICE_CONNS, addr: &conn->flags);
91 write_sequnlock(sl: &peer->service_conn_lock);
92 _leave(" = %d [new]", conn->debug_id);
93 return;
94
95found_extant_conn:
96 if (refcount_read(r: &cursor->ref) == 0)
97 goto replace_old_connection;
98 write_sequnlock(sl: &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
105replace_old_connection:
106 /* The old connection is from an outdated epoch. */
107 _debug("replace conn");
108 rb_replace_node_rcu(victim: &cursor->service_node,
109 new: &conn->service_node,
110 root: &peer->service_conns);
111 clear_bit(nr: RXRPC_CONN_IN_SERVICE_CONNS, addr: &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 */
119struct rxrpc_connection *rxrpc_prealloc_service_connection(struct rxrpc_net *rxnet,
120 gfp_t gfp)
121{
122 struct rxrpc_connection *conn = rxrpc_alloc_connection(rxnet, 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 refcount_set(r: &conn->ref, n: 2);
130
131 atomic_inc(v: &rxnet->nr_conns);
132 write_lock(&rxnet->conn_lock);
133 list_add_tail(new: &conn->link, head: &rxnet->service_conns);
134 list_add_tail(new: &conn->proc_link, head: &rxnet->conn_proc_list);
135 write_unlock(&rxnet->conn_lock);
136
137 rxrpc_see_connection(conn, rxrpc_conn_new_service);
138 }
139
140 return conn;
141}
142
143/*
144 * Set up an incoming connection. This is called in BH context with the RCU
145 * read lock held.
146 */
147void rxrpc_new_incoming_connection(struct rxrpc_sock *rx,
148 struct rxrpc_connection *conn,
149 const struct rxrpc_security *sec,
150 struct sk_buff *skb)
151{
152 struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
153
154 _enter("");
155
156 conn->proto.epoch = sp->hdr.epoch;
157 conn->proto.cid = sp->hdr.cid & RXRPC_CIDMASK;
158 conn->orig_service_id = sp->hdr.serviceId;
159 conn->service_id = sp->hdr.serviceId;
160 conn->security_ix = sp->hdr.securityIndex;
161 conn->out_clientflag = 0;
162 conn->security = sec;
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 atomic_set(v: &conn->active, i: 1);
177
178 /* Make the connection a target for incoming packets. */
179 rxrpc_publish_service_conn(peer: conn->peer, conn);
180}
181
182/*
183 * Remove the service connection from the peer's tree, thereby removing it as a
184 * target for incoming packets.
185 */
186void rxrpc_unpublish_service_conn(struct rxrpc_connection *conn)
187{
188 struct rxrpc_peer *peer = conn->peer;
189
190 write_seqlock(sl: &peer->service_conn_lock);
191 if (test_and_clear_bit(nr: RXRPC_CONN_IN_SERVICE_CONNS, addr: &conn->flags))
192 rb_erase(&conn->service_node, &peer->service_conns);
193 write_sequnlock(sl: &peer->service_conn_lock);
194}
195

source code of linux/net/rxrpc/conn_service.c