cregit-Linux how code gets into the kernel

Release 4.14 net/netfilter/xt_limit.c

Directory: net/netfilter
/* (C) 1999 Jérôme de Vivie <>
 * (C) 1999 Hervé Eychenne <>
 * (C) 2006-2012 Patrick McHardy <>
 * 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.

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/slab.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_limit.h>

struct xt_limit_priv {
spinlock_t lock;
unsigned long prev;
uint32_t credit;

MODULE_AUTHOR("Herve Eychenne <>");
MODULE_DESCRIPTION("Xtables: rate-limit match");

/* 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 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)


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 = jiffies; spin_lock_bh(&priv->lock); priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY; if (priv->credit > r->credit_cap) priv->credit = r->credit_cap; if (priv->credit >= r->cost) { /* We're not limited. */ priv->credit -= r->cost; spin_unlock_bh(&priv->lock); return true; } spin_unlock_bh(&priv->lock); return false; }


Linus Torvalds (pre-git)9975.57%112.50%
Jan Engelhardt2216.79%562.50%
Liping Zhang96.87%112.50%
Harald Welte10.76%112.50%

/* 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; }


Linus Torvalds (pre-git)4088.89%133.33%
Florian Westphal36.67%133.33%
Harald Welte24.44%133.33%

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("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); } spin_lock_init(&priv->lock); return 0; }


Linus Torvalds (pre-git)9456.63%17.14%
Jan Engelhardt5331.93%857.14%
Liping Zhang84.82%17.14%
Patrick McHardy84.82%214.29%
Florian Westphal21.20%17.14%
Harald Welte10.60%17.14%

static void limit_mt_destroy(const struct xt_mtdtor_param *par) { const struct xt_rateinfo *info = par->matchinfo; kfree(info->master); }


Jan Engelhardt29100.00%1100.00%

#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 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)); }


Patrick McHardy9196.81%125.00%
Jan Engelhardt33.19%375.00%

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; }


Patrick McHardy9797.00%125.00%
Jan Engelhardt33.00%375.00%

#endif /* CONFIG_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_COMPAT .compatsize = sizeof(struct compat_xt_rateinfo), .compat_from_user = limit_mt_compat_from_user, .compat_to_user = limit_mt_compat_to_user, #else .usersize = offsetof(struct xt_rateinfo, prev), #endif .me = THIS_MODULE, };
static int __init limit_mt_init(void) { return xt_register_match(&limit_mt_reg); }


Linus Torvalds (pre-git)1062.50%120.00%
Jan Engelhardt425.00%240.00%
Harald Welte16.25%120.00%
Patrick McHardy16.25%120.00%

static void __exit limit_mt_exit(void) { xt_unregister_match(&limit_mt_reg); }


Linus Torvalds (pre-git)853.33%120.00%
Jan Engelhardt426.67%240.00%
Harald Welte213.33%120.00%
Patrick McHardy16.67%120.00%

module_init(limit_mt_init); module_exit(limit_mt_exit);

Overall Contributors

Linus Torvalds (pre-git)28733.76%13.12%
Patrick McHardy27232.00%825.00%
Jan Engelhardt15217.88%1546.88%
Rusty Russell495.76%13.12%
Harald Welte424.94%26.25%
Liping Zhang202.35%13.12%
Willem de Bruijn131.53%13.12%
Art Haas70.82%13.12%
Florian Westphal50.59%13.12%
Tejun Heo30.35%13.12%
Directory: net/netfilter
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