1/*
2 * INETPEER - A storage for permanent information about peers
3 *
4 * This source is covered by the GNU GPL, the same as all kernel sources.
5 *
6 * Authors: Andrey V. Savochkin <saw@msu.ru>
7 */
8
9#include <linux/cache.h>
10#include <linux/module.h>
11#include <linux/types.h>
12#include <linux/slab.h>
13#include <linux/interrupt.h>
14#include <linux/spinlock.h>
15#include <linux/random.h>
16#include <linux/timer.h>
17#include <linux/time.h>
18#include <linux/kernel.h>
19#include <linux/mm.h>
20#include <linux/net.h>
21#include <linux/workqueue.h>
22#include <net/ip.h>
23#include <net/inetpeer.h>
24#include <net/secure_seq.h>
25
26/*
27 * Theory of operations.
28 * We keep one entry for each peer IP address. The nodes contains long-living
29 * information about the peer which doesn't depend on routes.
30 *
31 * Nodes are removed only when reference counter goes to 0.
32 * When it's happened the node may be removed when a sufficient amount of
33 * time has been passed since its last use. The less-recently-used entry can
34 * also be removed if the pool is overloaded i.e. if the total amount of
35 * entries is greater-or-equal than the threshold.
36 *
37 * Node pool is organised as an RB tree.
38 * Such an implementation has been chosen not just for fun. It's a way to
39 * prevent easy and efficient DoS attacks by creating hash collisions. A huge
40 * amount of long living nodes in a single hash slot would significantly delay
41 * lookups performed with disabled BHs.
42 *
43 * Serialisation issues.
44 * 1. Nodes may appear in the tree only with the pool lock held.
45 * 2. Nodes may disappear from the tree only with the pool lock held
46 * AND reference count being 0.
47 * 3. Global variable peer_total is modified under the pool lock.
48 * 4. struct inet_peer fields modification:
49 * rb_node: pool lock
50 * refcnt: atomically against modifications on other CPU;
51 * usually under some other lock to prevent node disappearing
52 * daddr: unchangeable
53 */
54
55static struct kmem_cache *peer_cachep __ro_after_init;
56
57void inet_peer_base_init(struct inet_peer_base *bp)
58{
59 bp->rb_root = RB_ROOT;
60 seqlock_init(&bp->lock);
61 bp->total = 0;
62}
63EXPORT_SYMBOL_GPL(inet_peer_base_init);
64
65#define PEER_MAX_GC 32
66
67/* Exported for sysctl_net_ipv4. */
68int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
69 * aggressively at this stage */
70int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
71int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
72
73/* Called from ip_output.c:ip_init */
74void __init inet_initpeers(void)
75{
76 struct sysinfo si;
77
78 /* Use the straight interface to information about memory. */
79 si_meminfo(&si);
80 /* The values below were suggested by Alexey Kuznetsov
81 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
82 * myself. --SAW
83 */
84 if (si.totalram <= (32768*1024)/PAGE_SIZE)
85 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
86 if (si.totalram <= (16384*1024)/PAGE_SIZE)
87 inet_peer_threshold >>= 1; /* about 512KB */
88 if (si.totalram <= (8192*1024)/PAGE_SIZE)
89 inet_peer_threshold >>= 2; /* about 128KB */
90
91 peer_cachep = kmem_cache_create("inet_peer_cache",
92 sizeof(struct inet_peer),
93 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
94 NULL);
95}
96
97/* Called with rcu_read_lock() or base->lock held */
98static struct inet_peer *lookup(const struct inetpeer_addr *daddr,
99 struct inet_peer_base *base,
100 unsigned int seq,
101 struct inet_peer *gc_stack[],
102 unsigned int *gc_cnt,
103 struct rb_node **parent_p,
104 struct rb_node ***pp_p)
105{
106 struct rb_node **pp, *parent, *next;
107 struct inet_peer *p;
108
109 pp = &base->rb_root.rb_node;
110 parent = NULL;
111 while (1) {
112 int cmp;
113
114 next = rcu_dereference_raw(*pp);
115 if (!next)
116 break;
117 parent = next;
118 p = rb_entry(parent, struct inet_peer, rb_node);
119 cmp = inetpeer_addr_cmp(daddr, &p->daddr);
120 if (cmp == 0) {
121 if (!refcount_inc_not_zero(&p->refcnt))
122 break;
123 return p;
124 }
125 if (gc_stack) {
126 if (*gc_cnt < PEER_MAX_GC)
127 gc_stack[(*gc_cnt)++] = p;
128 } else if (unlikely(read_seqretry(&base->lock, seq))) {
129 break;
130 }
131 if (cmp == -1)
132 pp = &next->rb_left;
133 else
134 pp = &next->rb_right;
135 }
136 *parent_p = parent;
137 *pp_p = pp;
138 return NULL;
139}
140
141static void inetpeer_free_rcu(struct rcu_head *head)
142{
143 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
144}
145
146/* perform garbage collect on all items stacked during a lookup */
147static void inet_peer_gc(struct inet_peer_base *base,
148 struct inet_peer *gc_stack[],
149 unsigned int gc_cnt)
150{
151 struct inet_peer *p;
152 __u32 delta, ttl;
153 int i;
154
155 if (base->total >= inet_peer_threshold)
156 ttl = 0; /* be aggressive */
157 else
158 ttl = inet_peer_maxttl
159 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
160 base->total / inet_peer_threshold * HZ;
161 for (i = 0; i < gc_cnt; i++) {
162 p = gc_stack[i];
163 delta = (__u32)jiffies - p->dtime;
164 if (delta < ttl || !refcount_dec_if_one(&p->refcnt))
165 gc_stack[i] = NULL;
166 }
167 for (i = 0; i < gc_cnt; i++) {
168 p = gc_stack[i];
169 if (p) {
170 rb_erase(&p->rb_node, &base->rb_root);
171 base->total--;
172 call_rcu(&p->rcu, inetpeer_free_rcu);
173 }
174 }
175}
176
177struct inet_peer *inet_getpeer(struct inet_peer_base *base,
178 const struct inetpeer_addr *daddr,
179 int create)
180{
181 struct inet_peer *p, *gc_stack[PEER_MAX_GC];
182 struct rb_node **pp, *parent;
183 unsigned int gc_cnt, seq;
184 int invalidated;
185
186 /* Attempt a lockless lookup first.
187 * Because of a concurrent writer, we might not find an existing entry.
188 */
189 rcu_read_lock();
190 seq = read_seqbegin(&base->lock);
191 p = lookup(daddr, base, seq, NULL, &gc_cnt, &parent, &pp);
192 invalidated = read_seqretry(&base->lock, seq);
193 rcu_read_unlock();
194
195 if (p)
196 return p;
197
198 /* If no writer did a change during our lookup, we can return early. */
199 if (!create && !invalidated)
200 return NULL;
201
202 /* retry an exact lookup, taking the lock before.
203 * At least, nodes should be hot in our cache.
204 */
205 parent = NULL;
206 write_seqlock_bh(&base->lock);
207
208 gc_cnt = 0;
209 p = lookup(daddr, base, seq, gc_stack, &gc_cnt, &parent, &pp);
210 if (!p && create) {
211 p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
212 if (p) {
213 p->daddr = *daddr;
214 p->dtime = (__u32)jiffies;
215 refcount_set(&p->refcnt, 2);
216 atomic_set(&p->rid, 0);
217 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
218 p->rate_tokens = 0;
219 p->n_redirects = 0;
220 /* 60*HZ is arbitrary, but chosen enough high so that the first
221 * calculation of tokens is at its maximum.
222 */
223 p->rate_last = jiffies - 60*HZ;
224
225 rb_link_node(&p->rb_node, parent, pp);
226 rb_insert_color(&p->rb_node, &base->rb_root);
227 base->total++;
228 }
229 }
230 if (gc_cnt)
231 inet_peer_gc(base, gc_stack, gc_cnt);
232 write_sequnlock_bh(&base->lock);
233
234 return p;
235}
236EXPORT_SYMBOL_GPL(inet_getpeer);
237
238void inet_putpeer(struct inet_peer *p)
239{
240 p->dtime = (__u32)jiffies;
241
242 if (refcount_dec_and_test(&p->refcnt))
243 call_rcu(&p->rcu, inetpeer_free_rcu);
244}
245EXPORT_SYMBOL_GPL(inet_putpeer);
246
247/*
248 * Check transmit rate limitation for given message.
249 * The rate information is held in the inet_peer entries now.
250 * This function is generic and could be used for other purposes
251 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
252 *
253 * Note that the same inet_peer fields are modified by functions in
254 * route.c too, but these work for packet destinations while xrlim_allow
255 * works for icmp destinations. This means the rate limiting information
256 * for one "ip object" is shared - and these ICMPs are twice limited:
257 * by source and by destination.
258 *
259 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
260 * SHOULD allow setting of rate limits
261 *
262 * Shared between ICMPv4 and ICMPv6.
263 */
264#define XRLIM_BURST_FACTOR 6
265bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
266{
267 unsigned long now, token;
268 bool rc = false;
269
270 if (!peer)
271 return true;
272
273 token = peer->rate_tokens;
274 now = jiffies;
275 token += now - peer->rate_last;
276 peer->rate_last = now;
277 if (token > XRLIM_BURST_FACTOR * timeout)
278 token = XRLIM_BURST_FACTOR * timeout;
279 if (token >= timeout) {
280 token -= timeout;
281 rc = true;
282 }
283 peer->rate_tokens = token;
284 return rc;
285}
286EXPORT_SYMBOL(inet_peer_xrlim_allow);
287
288void inetpeer_invalidate_tree(struct inet_peer_base *base)
289{
290 struct rb_node *p = rb_first(&base->rb_root);
291
292 while (p) {
293 struct inet_peer *peer = rb_entry(p, struct inet_peer, rb_node);
294
295 p = rb_next(p);
296 rb_erase(&peer->rb_node, &base->rb_root);
297 inet_putpeer(peer);
298 cond_resched();
299 }
300
301 base->total = 0;
302}
303EXPORT_SYMBOL(inetpeer_invalidate_tree);
304