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1275 |
phoenix |
/* Kernel module to control the rate
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*
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* Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
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* Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
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*
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* 2 September 1999: Changed from the target RATE to the match
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* `limit', removed logging. Did I mention that
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* Alexey is a fucking genius?
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* Rusty Russell (rusty@rustcorp.com.au). */
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/spinlock.h>
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#include <linux/interrupt.h>
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#include <linux/netfilter_ipv6/ip6_tables.h>
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#include <linux/netfilter_ipv6/ip6t_limit.h>
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/* The algorithm used is the Simple Token Bucket Filter (TBF)
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* see net/sched/sch_tbf.c in the linux source tree
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*/
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static spinlock_t limit_lock = SPIN_LOCK_UNLOCKED;
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/* Rusty: This is my (non-mathematically-inclined) understanding of
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this algorithm. The `average rate' in jiffies becomes your initial
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amount of credit `credit' and the most credit you can ever have
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`credit_cap'. The `peak rate' becomes the cost of passing the
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test, `cost'.
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`prev' tracks the last packet hit: you gain one credit per jiffy.
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If you get credit balance more than this, the extra credit is
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discarded. Every time the match passes, you lose `cost' credits;
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if you don't have that many, the test fails.
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See Alexey's formal explanation in net/sched/sch_tbf.c.
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To avoid underflow, we multiply by 128 (ie. you get 128 credits per
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jiffy). Hence a cost of 2^32-1, means one pass per 32768 seconds
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at 1024HZ (or one every 9 hours). A cost of 1 means 12800 passes
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per second at 100HZ. */
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#define CREDITS_PER_JIFFY 128
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static int
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ip6t_limit_match(const struct sk_buff *skb,
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const struct net_device *in,
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const struct net_device *out,
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const void *matchinfo,
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int offset,
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const void *hdr,
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u_int16_t datalen,
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int *hotdrop)
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{
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struct ip6t_rateinfo *r = ((struct ip6t_rateinfo *)matchinfo)->master;
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unsigned long now = jiffies;
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spin_lock_bh(&limit_lock);
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r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
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if (r->credit > r->credit_cap)
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r->credit = r->credit_cap;
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if (r->credit >= r->cost) {
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/* We're not limited. */
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r->credit -= r->cost;
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spin_unlock_bh(&limit_lock);
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return 1;
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}
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spin_unlock_bh(&limit_lock);
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return 0;
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}
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/* Precision saver. */
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static u_int32_t
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user2credits(u_int32_t user)
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{
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/* If multiplying would overflow... */
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if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
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/* Divide first. */
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return (user / IP6T_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
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return (user * HZ * CREDITS_PER_JIFFY) / IP6T_LIMIT_SCALE;
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}
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static int
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ip6t_limit_checkentry(const char *tablename,
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const struct ip6t_ip6 *ip,
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void *matchinfo,
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unsigned int matchsize,
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unsigned int hook_mask)
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{
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struct ip6t_rateinfo *r = matchinfo;
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if (matchsize != IP6T_ALIGN(sizeof(struct ip6t_rateinfo)))
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return 0;
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/* Check for overflow. */
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if (r->burst == 0
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|| user2credits(r->avg * r->burst) < user2credits(r->avg)) {
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printk("Call rusty: overflow in ip6t_limit: %u/%u\n",
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r->avg, r->burst);
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return 0;
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}
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/* User avg in seconds * IP6T_LIMIT_SCALE: convert to jiffies *
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128. */
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r->prev = jiffies;
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r->credit = user2credits(r->avg * r->burst); /* Credits full. */
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r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
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r->cost = user2credits(r->avg);
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/* For SMP, we only want to use one set of counters. */
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r->master = r;
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return 1;
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}
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static struct ip6t_match ip6t_limit_reg
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= { { NULL, NULL }, "limit", ip6t_limit_match, ip6t_limit_checkentry, NULL,
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THIS_MODULE };
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static int __init init(void)
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{
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if (ip6t_register_match(&ip6t_limit_reg))
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return -EINVAL;
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return 0;
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}
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static void __exit fini(void)
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{
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ip6t_unregister_match(&ip6t_limit_reg);
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}
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module_init(init);
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module_exit(fini);
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MODULE_LICENSE("GPL");
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