// 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 boollimit_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_obj(*priv);	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_COMPATstruct 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);