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