net/core/utils.c

   1 /*
   2  *      Generic address resultion entity
   3  *
   4  *      Authors:
   5  *      net_random Alan Cox
   6  *      net_ratelimit Andy Kleen
   7  *
   8  *      Created by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
   9  *
  10  *      This program is free software; you can redistribute it and/or
  11  *      modify it under the terms of the GNU General Public License
  12  *      as published by the Free Software Foundation; either version
  13  *      2 of the License, or (at your option) any later version.
  14  */
  15
  16 #include <asm/uaccess.h>
  17 #include <asm/system.h>
  18 #include <linux/types.h>
  19 #include <linux/kernel.h>
  20 #include <linux/sched.h>
  21 #include <linux/string.h>
  22 #include <linux/mm.h>
  23
  24 static unsigned long net_rand_seed = 152L;
  25
  26 unsigned long net_random(void)
  27 {
  28         net_rand_seed=net_rand_seed*69069L+1;
  29         return net_rand_seed^jiffies;
  30 }
  31
  32 void net_srandom(unsigned long entropy)
  33 {
  34         net_rand_seed ^= entropy;
  35         net_random();
  36 }
  37
  38 int net_msg_cost = 5*HZ;
  39 int net_msg_burst = 10*5*HZ;
  40
  41 /*
  42  * This enforces a rate limit: not more than one kernel message
  43  * every 5secs to make a denial-of-service attack impossible.
  44  *
  45  * All warning printk()s should be guarded by this function.
  46  */
  47 int net_ratelimit(void)
  48 {
  49         static unsigned long toks = 10*5*HZ;
  50         static unsigned long last_msg;
  51         static int missed;
  52         unsigned long now = jiffies;
  53
  54         toks += now - xchg(&last_msg, now);
  55         if (toks > net_msg_burst)
  56                 toks = net_msg_burst;
  57         if (toks >= net_msg_cost) {
  58                 toks -= net_msg_cost;
  59                 if (missed)
  60                         printk(KERN_WARNING "NET: %d messages suppressed.\n", missed);
  61                 missed = 0;
  62                 return 1;
  63         }
  64         missed++;
  65         return 0;
  66 }