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 = 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  */
  64 static 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);
  90 conn_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
  96 found_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
 106 replace_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  */
 120 struct 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  */
 148 void 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  */
 187 void 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 }