// SPDX-License-Identifier: GPL-2.0-only /* (C) 1999 Jérôme de Vivie * (C) 1999 Hervé Eychenne * (C) 2006-2012 Patrick McHardy */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include #include #include #include #include #include struct xt_limit_priv { unsigned long prev; u32 credit; }; MODULE_LICENSE("GPL"); MODULE_AUTHOR("Herve Eychenne "); MODULE_DESCRIPTION("Xtables: 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 */ /* 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 maximum 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 limit_mt(const struct sk_buff *skb, struct xt_action_param *par) { const struct xt_rateinfo *r = par->matchinfo; struct xt_limit_priv *priv = r->master; unsigned long now; u32 old_credit, new_credit, credit_increase = 0; bool ret; /* fastpath if there is nothing to update */ if ((READ_ONCE(priv->credit) < r->cost) && (READ_ONCE(priv->prev) == jiffies)) return false; do { now = jiffies; credit_increase += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY; old_credit = READ_ONCE(priv->credit); new_credit = old_credit; new_credit += credit_increase; if (new_credit > r->credit_cap) new_credit = r->credit_cap; if (new_credit >= r->cost) { ret = true; new_credit -= r->cost; } else { ret = false; } } while (cmpxchg(&priv->credit, old_credit, new_credit) != old_credit); return ret; } /* Precision saver. */ static u32 user2credits(u32 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 int limit_mt_check(const struct xt_mtchk_param *par) { struct xt_rateinfo *r = par->matchinfo; struct xt_limit_priv *priv; /* Check for overflow. */ if (r->burst == 0 || user2credits(r->avg * r->burst) < user2credits(r->avg)) { pr_info_ratelimited("Overflow, try lower: %u/%u\n", r->avg, r->burst); return -ERANGE; } priv = kmalloc(sizeof(*priv), GFP_KERNEL); if (priv == NULL) return -ENOMEM; /* For SMP, we only want to use one set of state. */ r->master = priv; /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 128. */ priv->prev = jiffies; priv->credit = user2credits(r->avg * r->burst); /* Credits full. */ if (r->cost == 0) { r->credit_cap = priv->credit; /* Credits full. */ r->cost = user2credits(r->avg); } return 0; } static void limit_mt_destroy(const struct xt_mtdtor_param *par) { const struct xt_rateinfo *info = par->matchinfo; kfree(info->master); } #ifdef CONFIG_NETFILTER_XTABLES_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 limit_mt_compat_from_user(void *dst, const 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 limit_mt_compat_to_user(void __user *dst, const 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_NETFILTER_XTABLES_COMPAT */ static struct xt_match limit_mt_reg __read_mostly = { .name = "limit", .revision = 0, .family = NFPROTO_UNSPEC, .match = limit_mt, .checkentry = limit_mt_check, .destroy = limit_mt_destroy, .matchsize = sizeof(struct xt_rateinfo), #ifdef CONFIG_NETFILTER_XTABLES_COMPAT .compatsize = sizeof(struct compat_xt_rateinfo), .compat_from_user = limit_mt_compat_from_user, .compat_to_user = limit_mt_compat_to_user, #endif .usersize = offsetof(struct xt_rateinfo, prev), .me = THIS_MODULE, }; static int __init limit_mt_init(void) { return xt_register_match(&limit_mt_reg); } static void __exit limit_mt_exit(void) { xt_unregister_match(&limit_mt_reg); } module_init(limit_mt_init); module_exit(limit_mt_exit);