utils.c

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/*
 *      Generic address resultion entity
 *
 *      Authors:
 *      net_random Alan Cox
 *      net_ratelimit Andy Kleen
 *
 *      Created by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

#include <asm/uaccess.h>
#include <asm/system.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>

static unsigned long net_rand_seed = 152L;

unsigned long net_random(void)
{
        net_rand_seed=net_rand_seed*69069L+1;
        return net_rand_seed^jiffies;
}

void net_srandom(unsigned long entropy)
{
        net_rand_seed ^= entropy;
        net_random();
}

int net_msg_cost = 5*HZ;
int net_msg_burst = 10*5*HZ;

/* 
 * This enforces a rate limit: not more than one kernel message
 * every 5secs to make a denial-of-service attack impossible.
 *
 * All warning printk()s should be guarded by this function. 
 */ 
int net_ratelimit(void)
{
        static spinlock_t ratelimit_lock = SPIN_LOCK_UNLOCKED;
        static unsigned long toks = 10*5*HZ;
        static unsigned long last_msg; 
        static int missed;
        unsigned long flags;
        unsigned long now = jiffies;

        spin_lock_irqsave(&ratelimit_lock, flags);
        toks += now - last_msg;
        last_msg = now;
        if (toks > net_msg_burst)
                toks = net_msg_burst;
        if (toks >= net_msg_cost) {
                int lost = missed;
                missed = 0;
                toks -= net_msg_cost;
                spin_unlock_irqrestore(&ratelimit_lock, flags);
                if (lost)
                        printk(KERN_WARNING "NET: %d messages suppressed.\n", lost);
                return 1;
        }
        missed++;
        spin_unlock_irqrestore(&ratelimit_lock, flags);
        return 0;
}

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