blob: 4fcca797150f75d7fc673196476ff101dfeecb05 [file] [log] [blame]
 /* (C) 1999 Jérôme de Vivie * (C) 1999 Hervé Eychenne * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */ #include #include #include #include #include #include MODULE_LICENSE("GPL"); MODULE_AUTHOR("Herve Eychenne "); MODULE_DESCRIPTION("iptables rate limit match"); MODULE_ALIAS("ipt_limit"); MODULE_ALIAS("ip6t_limit"); /* The algorithm used is the Simple Token Bucket Filter (TBF) * see net/sched/sch_tbf.c in the linux source tree */ static DEFINE_SPINLOCK(limit_lock); /* Rusty: This is my (non-mathematically-inclined) understanding of this algorithm. The `average rate' in jiffies becomes your initial amount of credit `credit' and the most credit you can ever have `credit_cap'. The `peak rate' becomes the cost of passing the test, `cost'. `prev' tracks the last packet hit: you gain one credit per jiffy. If you get credit balance more than this, the extra credit is discarded. Every time the match passes, you lose `cost' credits; if you don't have that many, the test fails. See Alexey's formal explanation in net/sched/sch_tbf.c. To get the maxmum range, we multiply by this factor (ie. you get N credits per jiffy). We want to allow a rate as low as 1 per day (slowest userspace tool allows), which means CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */ #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) /* Repeated shift and or gives us all 1s, final shift and add 1 gives * us the power of 2 below the theoretical max, so GCC simply does a * shift. */ #define _POW2_BELOW2(x) ((x)|((x)>>1)) #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) static bool ipt_limit_match(const struct sk_buff *skb, const struct net_device *in, const struct net_device *out, const struct xt_match *match, const void *matchinfo, int offset, unsigned int protoff, bool *hotdrop) { struct xt_rateinfo *r = ((const struct xt_rateinfo *)matchinfo)->master; unsigned long now = jiffies; spin_lock_bh(&limit_lock); r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY; if (r->credit > r->credit_cap) r->credit = r->credit_cap; if (r->credit >= r->cost) { /* We're not limited. */ r->credit -= r->cost; spin_unlock_bh(&limit_lock); return true; } spin_unlock_bh(&limit_lock); return false; } /* Precision saver. */ static u_int32_t user2credits(u_int32_t user) { /* If multiplying would overflow... */ if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) /* Divide first. */ return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE; } static bool ipt_limit_checkentry(const char *tablename, const void *inf, const struct xt_match *match, void *matchinfo, unsigned int hook_mask) { struct xt_rateinfo *r = matchinfo; /* Check for overflow. */ if (r->burst == 0 || user2credits(r->avg * r->burst) < user2credits(r->avg)) { printk("Overflow in xt_limit, try lower: %u/%u\n", r->avg, r->burst); return false; } /* For SMP, we only want to use one set of counters. */ r->master = r; if (r->cost == 0) { /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 128. */ r->prev = jiffies; r->credit = user2credits(r->avg * r->burst); /* Credits full. */ r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */ r->cost = user2credits(r->avg); } return true; } #ifdef CONFIG_COMPAT struct compat_xt_rateinfo { u_int32_t avg; u_int32_t burst; compat_ulong_t prev; u_int32_t credit; u_int32_t credit_cap, cost; u_int32_t master; }; /* To keep the full "prev" timestamp, the upper 32 bits are stored in the * master pointer, which does not need to be preserved. */ static void compat_from_user(void *dst, void *src) { const struct compat_xt_rateinfo *cm = src; struct xt_rateinfo m = { .avg = cm->avg, .burst = cm->burst, .prev = cm->prev | (unsigned long)cm->master << 32, .credit = cm->credit, .credit_cap = cm->credit_cap, .cost = cm->cost, }; memcpy(dst, &m, sizeof(m)); } static int compat_to_user(void __user *dst, void *src) { const struct xt_rateinfo *m = src; struct compat_xt_rateinfo cm = { .avg = m->avg, .burst = m->burst, .prev = m->prev, .credit = m->credit, .credit_cap = m->credit_cap, .cost = m->cost, .master = m->prev >> 32, }; return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0; } #endif /* CONFIG_COMPAT */ static struct xt_match xt_limit_match[] __read_mostly = { { .name = "limit", .family = AF_INET, .checkentry = ipt_limit_checkentry, .match = ipt_limit_match, .matchsize = sizeof(struct xt_rateinfo), #ifdef CONFIG_COMPAT .compatsize = sizeof(struct compat_xt_rateinfo), .compat_from_user = compat_from_user, .compat_to_user = compat_to_user, #endif .me = THIS_MODULE, }, { .name = "limit", .family = AF_INET6, .checkentry = ipt_limit_checkentry, .match = ipt_limit_match, .matchsize = sizeof(struct xt_rateinfo), .me = THIS_MODULE, }, }; static int __init xt_limit_init(void) { return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match)); } static void __exit xt_limit_fini(void) { xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match)); } module_init(xt_limit_init); module_exit(xt_limit_fini);