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 = 1;
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		seq++; /* 2 on the 1st/lockless path, otherwise odd */
39		read_seqbegin_or_lock(&peer->service_conn_lock, &seq);
40
41		p = rcu_dereference_raw(peer->service_conns.rb_node);
42		while (p) {
43			conn = rb_entry(p, struct rxrpc_connection, service_node);
44
45			if (conn->proto.index_key < k.index_key)
46				p = rcu_dereference_raw(p->rb_left);
47			else if (conn->proto.index_key > k.index_key)
48				p = rcu_dereference_raw(p->rb_right);
49			else
50				break;
51			conn = NULL;
52		}
53	} while (need_seqretry(&peer->service_conn_lock, seq));
54
55	done_seqretry(&peer->service_conn_lock, seq);
56	_leave(" = %d", conn ? conn->debug_id : -1);
57	return conn;
58}
59
60/*
61 * Insert a service connection into a peer's tree, thereby making it a target
62 * for incoming packets.
63 */
64static void rxrpc_publish_service_conn(struct rxrpc_peer *peer,
65				       struct rxrpc_connection *conn)
66{
67	struct rxrpc_connection *cursor = NULL;
68	struct rxrpc_conn_proto k = conn->proto;
69	struct rb_node **pp, *parent;
70
71	write_seqlock(&peer->service_conn_lock);
72
73	pp = &peer->service_conns.rb_node;
74	parent = NULL;
75	while (*pp) {
76		parent = *pp;
77		cursor = rb_entry(parent,
78				  struct rxrpc_connection, service_node);
79
80		if (cursor->proto.index_key < k.index_key)
81			pp = &(*pp)->rb_left;
82		else if (cursor->proto.index_key > k.index_key)
83			pp = &(*pp)->rb_right;
84		else
85			goto found_extant_conn;
86	}
87
88	rb_link_node_rcu(&conn->service_node, parent, pp);
89	rb_insert_color(&conn->service_node, &peer->service_conns);
90conn_published:
91	set_bit(RXRPC_CONN_IN_SERVICE_CONNS, &conn->flags);
92	write_sequnlock(&peer->service_conn_lock);
93	_leave(" = %d [new]", conn->debug_id);
94	return;
95
96found_extant_conn:
97	if (refcount_read(&cursor->ref) == 0)
98		goto replace_old_connection;
99	write_sequnlock(&peer->service_conn_lock);
100	/* We should not be able to get here.  rxrpc_incoming_connection() is
101	 * called in a non-reentrant context, so there can't be a race to
102	 * insert a new connection.
103	 */
104	BUG();
105
106replace_old_connection:
107	/* The old connection is from an outdated epoch. */
108	_debug("replace conn");
109	rb_replace_node_rcu(&cursor->service_node,
110			    &conn->service_node,
111			    &peer->service_conns);
112	clear_bit(RXRPC_CONN_IN_SERVICE_CONNS, &cursor->flags);
113	goto conn_published;
114}
115
116/*
117 * Preallocate a service connection.  The connection is placed on the proc and
118 * reap lists so that we don't have to get the lock from BH context.
119 */
120struct rxrpc_connection *rxrpc_prealloc_service_connection(struct rxrpc_net *rxnet,
121							   gfp_t gfp)
122{
123	struct rxrpc_connection *conn = rxrpc_alloc_connection(rxnet, gfp);
124
125	if (conn) {
126		/* We maintain an extra ref on the connection whilst it is on
127		 * the rxrpc_connections list.
128		 */
129		conn->state = RXRPC_CONN_SERVICE_PREALLOC;
130		refcount_set(&conn->ref, 2);
131
132		atomic_inc(&rxnet->nr_conns);
133		write_lock(&rxnet->conn_lock);
134		list_add_tail(&conn->link, &rxnet->service_conns);
135		list_add_tail(&conn->proc_link, &rxnet->conn_proc_list);
136		write_unlock(&rxnet->conn_lock);
137
138		rxrpc_see_connection(conn, rxrpc_conn_new_service);
139	}
140
141	return conn;
142}
143
144/*
145 * Set up an incoming connection.  This is called in BH context with the RCU
146 * read lock held.
147 */
148void rxrpc_new_incoming_connection(struct rxrpc_sock *rx,
149				   struct rxrpc_connection *conn,
150				   const struct rxrpc_security *sec,
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->orig_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	conn->security		= sec;
164	if (conn->security_ix)
165		conn->state	= RXRPC_CONN_SERVICE_UNSECURED;
166	else
167		conn->state	= RXRPC_CONN_SERVICE;
168
169	/* See if we should upgrade the service.  This can only happen on the
170	 * first packet on a new connection.  Once done, it applies to all
171	 * subsequent calls on that connection.
172	 */
173	if (sp->hdr.userStatus == RXRPC_USERSTATUS_SERVICE_UPGRADE &&
174	    conn->service_id == rx->service_upgrade.from)
175		conn->service_id = rx->service_upgrade.to;
176
177	atomic_set(&conn->active, 1);
178
179	/* Make the connection a target for incoming packets. */
180	rxrpc_publish_service_conn(conn->peer, conn);
181}
182
183/*
184 * Remove the service connection from the peer's tree, thereby removing it as a
185 * target for incoming packets.
186 */
187void rxrpc_unpublish_service_conn(struct rxrpc_connection *conn)
188{
189	struct rxrpc_peer *peer = conn->peer;
190
191	write_seqlock(&peer->service_conn_lock);
192	if (test_and_clear_bit(RXRPC_CONN_IN_SERVICE_CONNS, &conn->flags))
193		rb_erase(&conn->service_node, &peer->service_conns);
194	write_sequnlock(&peer->service_conn_lock);
195}
196