net/ipv4/inetpeer.c

   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
 163                 /* The READ_ONCE() pairs with the WRITE_ONCE()
 164                  * in inet_putpeer()
 165                  */
 166                 delta = (__u32)jiffies - READ_ONCE(p->dtime);
 167
 168                 if (delta < ttl || !refcount_dec_if_one(&p->refcnt))
 169                         gc_stack[i] = NULL;
 170         }
 171         for (i = 0; i < gc_cnt; i++) {
 172                 p = gc_stack[i];
 173                 if (p) {
 174                         rb_erase(&p->rb_node, &base->rb_root);
 175                         base->total--;
 176                         call_rcu(&p->rcu, inetpeer_free_rcu);
 177                 }
 178         }
 179 }
 180
 181 struct inet_peer *inet_getpeer(struct inet_peer_base *base,
 182                                const struct inetpeer_addr *daddr,
 183                                int create)
 184 {
 185         struct inet_peer *p, *gc_stack[PEER_MAX_GC];
 186         struct rb_node **pp, *parent;
 187         unsigned int gc_cnt, seq;
 188         int invalidated;
 189
 190         /* Attempt a lockless lookup first.
 191          * Because of a concurrent writer, we might not find an existing entry.
 192          */
 193         rcu_read_lock();
 194         seq = read_seqbegin(&base->lock);
 195         p = lookup(daddr, base, seq, NULL, &gc_cnt, &parent, &pp);
 196         invalidated = read_seqretry(&base->lock, seq);
 197         rcu_read_unlock();
 198
 199         if (p)
 200                 return p;
 201
 202         /* If no writer did a change during our lookup, we can return early. */
 203         if (!create && !invalidated)
 204                 return NULL;
 205
 206         /* retry an exact lookup, taking the lock before.
 207          * At least, nodes should be hot in our cache.
 208          */
 209         parent = NULL;
 210         write_seqlock_bh(&base->lock);
 211
 212         gc_cnt = 0;
 213         p = lookup(daddr, base, seq, gc_stack, &gc_cnt, &parent, &pp);
 214         if (!p && create) {
 215                 p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
 216                 if (p) {
 217                         p->daddr = *daddr;
 218                         p->dtime = (__u32)jiffies;
 219                         refcount_set(&p->refcnt, 2);
 220                         atomic_set(&p->rid, 0);
 221                         p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
 222                         p->rate_tokens = 0;
 223                         p->n_redirects = 0;
 224                         /* 60*HZ is arbitrary, but chosen enough high so that the first
 225                          * calculation of tokens is at its maximum.
 226                          */
 227                         p->rate_last = jiffies - 60*HZ;
 228
 229                         rb_link_node(&p->rb_node, parent, pp);
 230                         rb_insert_color(&p->rb_node, &base->rb_root);
 231                         base->total++;
 232                 }
 233         }
 234         if (gc_cnt)
 235                 inet_peer_gc(base, gc_stack, gc_cnt);
 236         write_sequnlock_bh(&base->lock);
 237
 238         return p;
 239 }
 240 EXPORT_SYMBOL_GPL(inet_getpeer);
 241
 242 void inet_putpeer(struct inet_peer *p)
 243 {
 244         /* The WRITE_ONCE() pairs with itself (we run lockless)
 245          * and the READ_ONCE() in inet_peer_gc()
 246          */
 247         WRITE_ONCE(p->dtime, (__u32)jiffies);
 248
 249         if (refcount_dec_and_test(&p->refcnt))
 250                 call_rcu(&p->rcu, inetpeer_free_rcu);
 251 }
 252 EXPORT_SYMBOL_GPL(inet_putpeer);
 253
 254 /*
 255  *      Check transmit rate limitation for given message.
 256  *      The rate information is held in the inet_peer entries now.
 257  *      This function is generic and could be used for other purposes
 258  *      too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
 259  *
 260  *      Note that the same inet_peer fields are modified by functions in
 261  *      route.c too, but these work for packet destinations while xrlim_allow
 262  *      works for icmp destinations. This means the rate limiting information
 263  *      for one "ip object" is shared - and these ICMPs are twice limited:
 264  *      by source and by destination.
 265  *
 266  *      RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
 267  *                        SHOULD allow setting of rate limits
 268  *
 269  *      Shared between ICMPv4 and ICMPv6.
 270  */
 271 #define XRLIM_BURST_FACTOR 6
 272 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
 273 {
 274         unsigned long now, token;
 275         bool rc = false;
 276
 277         if (!peer)
 278                 return true;
 279
 280         token = peer->rate_tokens;
 281         now = jiffies;
 282         token += now - peer->rate_last;
 283         peer->rate_last = now;
 284         if (token > XRLIM_BURST_FACTOR * timeout)
 285                 token = XRLIM_BURST_FACTOR * timeout;
 286         if (token >= timeout) {
 287                 token -= timeout;
 288                 rc = true;
 289         }
 290         peer->rate_tokens = token;
 291         return rc;
 292 }
 293 EXPORT_SYMBOL(inet_peer_xrlim_allow);
 294
 295 void inetpeer_invalidate_tree(struct inet_peer_base *base)
 296 {
 297         struct rb_node *p = rb_first(&base->rb_root);
 298
 299         while (p) {
 300                 struct inet_peer *peer = rb_entry(p, struct inet_peer, rb_node);
 301
 302                 p = rb_next(p);
 303                 rb_erase(&peer->rb_node, &base->rb_root);
 304                 inet_putpeer(peer);
 305                 cond_resched();
 306         }
 307
 308         base->total = 0;
 309 }
 310 EXPORT_SYMBOL(inetpeer_invalidate_tree);