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/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                         /* 60*HZ is arbitrary, but chosen enough high so that the first
 220                          * calculation of tokens is at its maximum.
 221                          */
 222                         p->rate_last = jiffies - 60*HZ;
 223
 224                         rb_link_node(&p->rb_node, parent, pp);
 225                         rb_insert_color(&p->rb_node, &base->rb_root);
 226                         base->total++;
 227                 }
 228         }
 229         if (gc_cnt)
 230                 inet_peer_gc(base, gc_stack, gc_cnt);
 231         write_sequnlock_bh(&base->lock);
 232
 233         return p;
 234 }
 235 EXPORT_SYMBOL_GPL(inet_getpeer);
 236
 237 void inet_putpeer(struct inet_peer *p)
 238 {
 239         p->dtime = (__u32)jiffies;
 240
 241         if (refcount_dec_and_test(&p->refcnt))
 242                 call_rcu(&p->rcu, inetpeer_free_rcu);
 243 }
 244 EXPORT_SYMBOL_GPL(inet_putpeer);
 245
 246 /*
 247  *      Check transmit rate limitation for given message.
 248  *      The rate information is held in the inet_peer entries now.
 249  *      This function is generic and could be used for other purposes
 250  *      too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
 251  *
 252  *      Note that the same inet_peer fields are modified by functions in
 253  *      route.c too, but these work for packet destinations while xrlim_allow
 254  *      works for icmp destinations. This means the rate limiting information
 255  *      for one "ip object" is shared - and these ICMPs are twice limited:
 256  *      by source and by destination.
 257  *
 258  *      RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
 259  *                        SHOULD allow setting of rate limits
 260  *
 261  *      Shared between ICMPv4 and ICMPv6.
 262  */
 263 #define XRLIM_BURST_FACTOR 6
 264 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
 265 {
 266         unsigned long now, token;
 267         bool rc = false;
 268
 269         if (!peer)
 270                 return true;
 271
 272         token = peer->rate_tokens;
 273         now = jiffies;
 274         token += now - peer->rate_last;
 275         peer->rate_last = now;
 276         if (token > XRLIM_BURST_FACTOR * timeout)
 277                 token = XRLIM_BURST_FACTOR * timeout;
 278         if (token >= timeout) {
 279                 token -= timeout;
 280                 rc = true;
 281         }
 282         peer->rate_tokens = token;
 283         return rc;
 284 }
 285 EXPORT_SYMBOL(inet_peer_xrlim_allow);
 286
 287 void inetpeer_invalidate_tree(struct inet_peer_base *base)
 288 {
 289         struct rb_node *p = rb_first(&base->rb_root);
 290
 291         while (p) {
 292                 struct inet_peer *peer = rb_entry(p, struct inet_peer, rb_node);
 293
 294                 p = rb_next(p);
 295                 rb_erase(&peer->rb_node, &base->rb_root);
 296                 inet_putpeer(peer);
 297                 cond_resched();
 298         }
 299
 300         base->total = 0;
 301 }
 302 EXPORT_SYMBOL(inetpeer_invalidate_tree);