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 | |
55 | static struct kmem_cache *peer_cachep __ro_after_init; |
56 | |
57 | void 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 | } |
63 | EXPORT_SYMBOL_GPL(inet_peer_base_init); |
64 | |
65 | #define PEER_MAX_GC 32 |
66 | |
67 | /* Exported for sysctl_net_ipv4. */ |
68 | int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more |
69 | * aggressively at this stage */ |
70 | int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */ |
71 | int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */ |
72 | |
73 | /* Called from ip_output.c:ip_init */ |
74 | void __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 */ |
98 | static 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 | |
141 | static 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 */ |
147 | static 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 | |
177 | struct 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 | } |
236 | EXPORT_SYMBOL_GPL(inet_getpeer); |
237 | |
238 | void 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 | } |
245 | EXPORT_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 |
265 | bool 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 | } |
286 | EXPORT_SYMBOL(inet_peer_xrlim_allow); |
287 | |
288 | void 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 | } |
303 | EXPORT_SYMBOL(inetpeer_invalidate_tree); |
304 | |