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 
net_random(void)26 unsigned long net_random(void)
27 {
28 	net_rand_seed=net_rand_seed*69069L+1;
29         return net_rand_seed^jiffies;
30 }
31 
net_srandom(unsigned long entropy)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  */
net_ratelimit(void)47 int net_ratelimit(void)
48 {
49 	static spinlock_t ratelimit_lock = SPIN_LOCK_UNLOCKED;
50 	static unsigned long toks = 10*5*HZ;
51 	static unsigned long last_msg;
52 	static int missed;
53 	unsigned long flags;
54 	unsigned long now = jiffies;
55 
56 	spin_lock_irqsave(&ratelimit_lock, flags);
57 	toks += now - last_msg;
58 	last_msg = now;
59 	if (toks > net_msg_burst)
60 		toks = net_msg_burst;
61 	if (toks >= net_msg_cost) {
62 		int lost = missed;
63 		missed = 0;
64 		toks -= net_msg_cost;
65 		spin_unlock_irqrestore(&ratelimit_lock, flags);
66 		if (lost)
67 			printk(KERN_WARNING "NET: %d messages suppressed.\n", lost);
68 		return 1;
69 	}
70 	missed++;
71 	spin_unlock_irqrestore(&ratelimit_lock, flags);
72 	return 0;
73 }
74