基于连接的每IP限速实现
在《修改netfilter的limit模块实现基于单个ip的流量监控》中，介绍了一种方式实现针对一个网段每个IP地址的流量控制，如果细化到流，那个就叫做针对每个流的流量控制，我们知道，一个IP地址可以和很多流相关联，针对流的流控限制的不是主机，而是主机上的一个连接，它的约束要比针对IP地址的流控更加小。
然而如何来实现这个呢？实际上在Linux中，几乎所有的流控都可以用TC工具配置出来，然而还有一种方式，那就是使用Netfilter来实现，然后用iptables来配置，这正是体现了Netfilter框架的灵活和强大，当然使用TC也未尝不可，只是TC虽强大，然则功能比较单一，不像Netfilter一样可以扩展到几乎无限制的应用场合。
实现很简单，还是修改limit模块，这次连iptables模块都不用写了，这是改变了iptables对应模块的语义，源代码如下所示：
/* (C) 1999 Jér?me de Vivie <devivie@info.enserb.u-bordeaux.fr> * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr> * * 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 <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>#include <net/netfilter/nf_conntrack.h>#include <net/netfilter/nf_conntrack_extend.h>//针对每一个方向给一个流量约束struct xt_limit_priv { unsigned long prev[2]; uint32_t credit[2];};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 */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)//定义一个conntrack的extensionstatic struct nf_ct_ext_type limit_extend __read_mostly = { .len = sizeof(struct xt_limit_priv), .align = __alignof__(struct xt_limit_priv), .id = NF_CT_EXT_LIMIT,};static u_int32_t user2credits(u_int32_t user);static boollimit_mt(const struct sk_buff *skb, const struct xt_match_param *par){ const struct xt_rateinfo *r = par->matchinfo; struct nf_conn *ct; enum ip_conntrack_info ctinfo; struct xt_limit_priv *priv; unsigned long now = jiffies; int dir = 1; ct = nf_ct_get(skb, &ctinfo); priv = nf_ct_ext_find(ct, NF_CT_EXT_LIMIT); if(priv == NULL) { if (nf_ct_is_confirmed(ct)) return false; priv = nf_ct_ext_add(ct, NF_CT_EXT_LIMIT, GFP_ATOMIC); if (priv == NULL) { printk("failed to add LIMIT extension\n"); return false; } priv->prev[0] = priv->prev[1] = jiffies; priv->credit[0] = priv->credit[1] = user2credits(r->avg * r->burst); /* Credits full. */ } //和DIR相关的元素保存在skb中而不是conntrack中，这样可以最小化锁的开销，因为一个流的数据包的方向是双向的，何时到来并不清楚，如果在conntrack中保存方向，将无法实现两个方向的并行处理。 dir = CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL ? 1 : 0; spin_lock_bh(&limit_lock); priv->credit[dir] += (now - xchg(&priv->prev[dir], now)) * CREDITS_PER_JIFFY; if (priv->credit[dir] > r->credit_cap) priv->credit[dir] = r->credit_cap; if (priv->credit[dir] >= r->cost) { /* We're not limited. */ priv->credit[dir] -= skb->len; spin_unlock_bh(&limit_lock); return true; } spin_unlock_bh(&limit_lock); return false;}/* Precision saver. */static u_int32_tuser2credits(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 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)) { printk("Overflow in xt_limit, try lower: %u/%u\n", r->avg, r->burst); return false; } priv = kmalloc(sizeof(*priv), GFP_KERNEL); if (priv == NULL) return false; /* For SMP, we only want to use one set of state. */ r->master = priv; if (r->cost == 0) { /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 128. */ priv->prev[0] = priv->prev[1] = jiffies; priv->credit[0] = priv->credit[1] = user2credits(r->avg * r->burst); /* Credits full. */ r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */ r->cost = user2credits(r->avg); } return true;}static void limit_mt_destroy(const struct xt_mtdtor_param *par){ const struct xt_rateinfo *info = par->matchinfo; kfree(info->master);}#ifdef CONFIG_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, 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, 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 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,#endif .me = THIS_MODULE,};static int __init limit_mt_init(void){ int rv = xt_register_match(&limit_mt_reg); if (rv < 0) { return rv; } return nf_ct_extend_register(&limit_extend);}static void __exit limit_mt_exit(void){ xt_unregister_match(&limit_mt_reg);}module_init(limit_mt_init);module_exit(limit_mt_exit);