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Diffstat (limited to 'net/netfilter/xt_limit.c')
-rw-r--r-- | net/netfilter/xt_limit.c | 215 |
1 files changed, 215 insertions, 0 deletions
diff --git a/net/netfilter/xt_limit.c b/net/netfilter/xt_limit.c new file mode 100644 index 000000000..8b4fd2785 --- /dev/null +++ b/net/netfilter/xt_limit.c @@ -0,0 +1,215 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr> + * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr> + * (C) 2006-2012 Patrick McHardy <kaber@trash.net> + */ +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/slab.h> +#include <linux/module.h> +#include <linux/skbuff.h> +#include <linux/interrupt.h> + +#include <linux/netfilter/x_tables.h> +#include <linux/netfilter/xt_limit.h> + +struct xt_limit_priv { + unsigned long prev; + u32 credit; +}; + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); +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); |