arp.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		This file implements the Address Resolution Protocol (ARP),
 *		which is used by TCP/IP to map the IP addresses from a host
 *		to a low-level hardware address (like an Ethernet address)
 *		which it can use to talk to that host.
 *
 * NOTE:	This module will be rewritten completely in the near future,
 *		because I want it to become a multi-address-family address
 *		resolver, like it should be.  It will be put in a separate
 *		directory under 'net', being a protocol of its own. -FvK
 *
 * Version:	@(#)arp.c	1.0.15	05/25/93
 *
 * Authors:	Ross Biro, <[e-mail]>
 *		Fred N. van Kempen, <[e-mail]>
 *		Arnt Gulbrandsen, <[e-mail]>
 *
 * Fixes:
 *		Stephen A. Wood	:	arp problems
 *		'Mr Linux'	:	arp problems.
 *		Alan Cox	:	arp_ioctl now checks memory areas with verify_area.
 *		Alan Cox	:	Non IP arp message now only appears with debugging on.
 *		Alan Cox	: 	arp queue is volatile (may be altered by arp messages while doing sends) 
 *					Generic queue code is urgently needed!
 *		Alan Cox	:	Deleting your own ip addr now gives EINVAL not a printk message.
 *		Alan Cox	:	Fix to arp linked list error
 *		Alan Cox	:	Ignore broadcast arp (Linus' idea 8-))
 *		Alan Cox	:	arp_send memory leak removed
 *		Alan Cox	:	generic skbuff code fixes.
 *		Alan Cox	:	'Bad Packet' only reported on debugging
 *		Alan Cox	:	Proxy arp.
 *		Alan Cox	:	skb->link3 maintained by letting the other xmit queue kill the packet.
 *		Alan Cox	:	Knows about type 3 devices (AX.25) using an AX.25 protocol ID not the ethernet
 *					one.
 *		Dominik Kubla	:	Better checking
 *		Tegge		:	Assorted corrections on cross port stuff
 *		Alan Cox	:	ATF_PERM was backwards! - might be useful now (sigh)
 *		Alan Cox	:	Arp timer added.
 *
 * To Fix:
 *				:	arp response allocates an skbuff to send. However there is a perfectly
 *					good spare skbuff the right size about to be freed (the query). Use the
 *					query for the reply. This avoids an out of memory case _and_ speeds arp
 *					up.
 *				:	FREE_READ v FREE_WRITE errors. Not critical as loopback arps don't occur
 *
 *
 *		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 <linux/types.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/config.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/timer.h>
#include <linux/errno.h>
#include <linux/if_arp.h>
#include <linux/in.h>
#include <asm/system.h>
#include <asm/segment.h>
#include <stdarg.h>
#include "inet.h"
#include "dev.h"
#include "eth.h"
#include "ip.h"
#include "route.h"
#include "protocol.h"
#include "tcp.h"
#include "skbuff.h"
#include "sock.h"
#include "arp.h"


#define ARP_MAX_TRIES	3


static char *unk_print(unsigned char *, int);
static char *eth_aprint(unsigned char *, int);


static char *arp_cmds[] = {
  "0x%04X",
  "REQUEST",
  "REPLY",
  "REVERSE REQUEST",
  "REVERSE REPLY",
  NULL
};
#define	ARP_MAX_CMDS	(sizeof(arp_cmds) / sizeof(arp_cmds[0]))

static struct {
  char	*name;
  char	*(*print)(unsigned char *ptr, int len);
} arp_types[] = {
  { "0x%04X",			unk_print	},
  { "10 Mbps Ethernet", 	eth_aprint	},
  { "3 Mbps Ethernet",		eth_aprint	},
  { "AX.25",			unk_print	},
  { "Pronet",			unk_print	},
  { "Chaos",			unk_print	},
  { "IEEE 802.2 Ethernet (?)",	eth_aprint	},
  { "Arcnet",			unk_print	},
  { "AppleTalk",		unk_print	},
  { NULL,			NULL		}
};
#define	ARP_MAX_TYPE	(sizeof(arp_types) / sizeof(arp_types[0]))


struct arp_table *arp_tables[ARP_TABLE_SIZE] = {
  NULL,
};

static int arp_proxies=0;	/* So we can avoid the proxy arp 
				   overhead with the usual case of
				   no proxy arps */

struct sk_buff * volatile arp_q = NULL;

static struct arp_table *arp_lookup(unsigned long addr);
static struct arp_table *arp_lookup_proxy(unsigned long addr);

/* Dump the ADDRESS bytes of an unknown hardware type. */
static char *
unk_print(unsigned char *ptr, int len)
{
  static char buff[32];
  char *bufp = buff;
  int i;

  for (i = 0; i < len; i++)
	bufp += sprintf(bufp, "%02X ", (*ptr++ & 0377));
  return(buff);
}


/* Dump the ADDRESS bytes of an Ethernet hardware type. */
static char *
eth_aprint(unsigned char *ptr, int len)
{
  if (len != ETH_ALEN) return("");
  return(eth_print(ptr));
}


/* Dump an ARP packet. Not complete yet for non-Ethernet packets. */
static void
arp_print(struct arphdr *arp)
{
  int len, idx;
  unsigned char *ptr;

  if (inet_debug != DBG_ARP) return;

  printk("ARP: ");
  if (arp == NULL) {
	printk("(null)\n");
	return;
  }

  /* Print the opcode name. */
  len = htons(arp->ar_op);
  if (len < ARP_MAX_CMDS) idx = len;
    else idx = 0;
  printk("op ");
  printk(arp_cmds[idx], len);

  /* Print the ARP header. */
  len = htons(arp->ar_hrd);
  if (len < ARP_MAX_TYPE) idx = len;
    else idx = 0;
  printk("   hrd = "); printk(arp_types[idx].name, len);
  printk("   pro = 0x%04X\n", htons(arp->ar_pro));
  printk("   hlen = %d plen = %d\n", arp->ar_hln, arp->ar_pln);

  /*
   * Print the variable data.
   * When ARP gets redone (after the formal introduction of NET-2),
   * this part will be redone.  ARP will then be a multi-family address
   * resolver, and the code below will be made more general. -FvK
   */
  ptr = ((unsigned char *) &arp->ar_op) + sizeof(u_short);
  printk("   sender HA = %s ", arp_types[idx].print(ptr, arp->ar_hln));
  ptr += arp->ar_hln;
  printk("  PA = %s\n", in_ntoa(*(unsigned long *) ptr));
  ptr += arp->ar_pln;
  printk("   target HA = %s ", arp_types[idx].print(ptr, arp->ar_hln));
  ptr += arp->ar_hln;
  printk("  PA = %s\n", in_ntoa(*(unsigned long *) ptr));
}


/* This will try to retransmit everything on the queue. */
static void
arp_send_q(void)
{
  struct sk_buff *skb;
  struct sk_buff *volatile work_q;
  cli();
  work_q = arp_q;
  skb_new_list_head(&work_q);
  arp_q = NULL;
  sti();
  while((skb=skb_dequeue(&work_q))!=NULL)
  {
  	IS_SKB(skb);
	skb->magic = 0;
	skb->next = NULL;
	skb->prev = NULL;

	/* Decrement the 'tries' counter. */
	cli();
	skb->tries--;
	if (skb->tries == 0) {
		/*
		 * Grmpf.
		 * We have tried ARP_MAX_TRIES to resolve the IP address
		 * from this datagram.  This means that the machine does
		 * not listen to our ARP requests.  Perhaps someone tur-
		 * ned off the thing?
		 * In any case, trying further is useless.  So, we kill
		 * this packet from the queue.  (grinnik) -FvK
		 */
		skb->sk = NULL;
		if(skb->free)
			kfree_skb(skb, FREE_WRITE);
			/* If free was 0, magic is now 0, next is 0 and 
			   the write queue will notice and kill */
		sti();
		continue;
	}

	/* Can we now complete this packet? */
	sti();
	if (skb->arp || !skb->dev->rebuild_header(skb->data, skb->dev)) {
		skb->arp  = 1;
		skb->dev->queue_xmit(skb, skb->dev, 0);
	} else {
		/* Alas.  Re-queue it... */
		skb->magic = ARP_QUEUE_MAGIC;      
		skb_queue_head(&arp_q,skb);
	}
  }
}


static struct timer_list arp_timer;

static void arp_queue_ticker(unsigned long data);

static void arp_queue_kick(void)
{
	arp_timer.expires = 500;	/* 5 seconds */
	arp_timer.data = 0;
	arp_timer.function = arp_queue_ticker;
	del_timer(&arp_timer);
	add_timer(&arp_timer);
}

static void arp_queue_ticker(unsigned long data/*UNUSED*/)
{
	arp_send_q();
	if (skb_peek(&arp_q))
		arp_queue_kick();
}



/* Create and send our response to an ARP request. */
static int
arp_response(struct arphdr *arp1, struct device *dev,  int addrtype)
{
  struct arphdr *arp2;
  struct sk_buff *skb;
  unsigned long src, dst;
  unsigned char *ptr1, *ptr2;
  int hlen;
  struct arp_table *apt = NULL;/* =NULL otherwise the compiler gives warnings */

  /* Decode the source (REQUEST) message. */
  ptr1 = ((unsigned char *) &arp1->ar_op) + sizeof(u_short);
  src = *((unsigned long *) (ptr1 + arp1->ar_hln));
  dst = *((unsigned long *) (ptr1 + (arp1->ar_hln * 2) + arp1->ar_pln));
  
  if(addrtype!=IS_MYADDR)
  {
  	apt=arp_lookup_proxy(dst);
  	if(apt==NULL)
  		return(1);
  }

  /* Get some mem and initialize it for the return trip. */
  skb = alloc_skb(sizeof(struct sk_buff) +
  		sizeof(struct arphdr) +
		(2 * arp1->ar_hln) + (2 * arp1->ar_pln) +
		dev->hard_header_len, GFP_ATOMIC);
  if (skb == NULL) {
	printk("ARP: no memory available for ARP REPLY!\n");
	return(1);
  }

  skb->mem_addr = skb;
  skb->len      = sizeof(struct arphdr) + (2 * arp1->ar_hln) + 
		  (2 * arp1->ar_pln) + dev->hard_header_len;
  skb->mem_len  = sizeof(struct sk_buff) + skb->len;
  hlen = dev->hard_header(skb->data, dev, ETH_P_ARP, src, dst, skb->len);
  if (hlen < 0) {
	printk("ARP: cannot create HW frame header for REPLY !\n");
	kfree_skb(skb, FREE_WRITE);
	return(1);
  }

  /*
   * Fill in the ARP REPLY packet.
   * This looks ugly, but we have to deal with the variable-length
   * ARP packets and such.  It is not as bad as it looks- FvK
   */
  arp2 = (struct arphdr *) (skb->data + hlen);
  ptr2 = ((unsigned char *) &arp2->ar_op) + sizeof(u_short);
  arp2->ar_hrd = arp1->ar_hrd;
  arp2->ar_pro = arp1->ar_pro;
  arp2->ar_hln = arp1->ar_hln;
  arp2->ar_pln = arp1->ar_pln;
  arp2->ar_op = htons(ARPOP_REPLY);
  if(addrtype==IS_MYADDR)
	  memcpy(ptr2, dev->dev_addr, arp2->ar_hln);
  else		/* Proxy arp, so pull from the table */
  	  memcpy(ptr2, apt->ha, arp2->ar_hln);
  ptr2 += arp2->ar_hln;
  memcpy(ptr2, ptr1 + (arp1->ar_hln * 2) + arp1->ar_pln, arp2->ar_pln);
  ptr2 += arp2->ar_pln;
  memcpy(ptr2, ptr1, arp2->ar_hln);
  ptr2 += arp2->ar_hln;
  memcpy(ptr2, ptr1 + arp1->ar_hln, arp2->ar_pln);

  skb->free = 1;
  skb->arp = 1;
  skb->sk = NULL;
  skb->next = NULL;

  DPRINTF((DBG_ARP, ">>"));
  arp_print(arp2);

  /* Queue the packet for transmission. */
  dev->queue_xmit(skb, dev, 0);
  return(0);
}


/* This will find an entry in the ARP table by looking at the IP address. */
static struct arp_table *
arp_lookup(unsigned long paddr)
{
  struct arp_table *apt;
  unsigned long hash;

  DPRINTF((DBG_ARP, "ARP: lookup(%s)\n", in_ntoa(paddr)));

  /* We don't want to ARP ourselves. */
  if (chk_addr(paddr) == IS_MYADDR) {
	printk("ARP: ARPing my own IP address %s !\n", in_ntoa(paddr));
	return(NULL);
  }

  /* Loop through the table for the desired address. */
  hash = htonl(paddr) & (ARP_TABLE_SIZE - 1);
  cli();
  apt = arp_tables[hash];
  while(apt != NULL) {
	if (apt->ip == paddr) {
		sti();
		return(apt);
	}
	apt = apt->next;
  }
  sti();
  return(NULL);
}


/* This will find a proxy in the ARP table by looking at the IP address. */
static struct arp_table *arp_lookup_proxy(unsigned long paddr)
{
  struct arp_table *apt;
  unsigned long hash;

  DPRINTF((DBG_ARP, "ARP: lookup proxy(%s)\n", in_ntoa(paddr)));

  /* Loop through the table for the desired address. */
  hash = htonl(paddr) & (ARP_TABLE_SIZE - 1);
  cli();
  apt = arp_tables[hash];
  while(apt != NULL) {
	if (apt->ip == paddr && (apt->flags & ATF_PUBL) ) {
		sti();
		return(apt);
	}
	apt = apt->next;
  }
  sti();
  return(NULL);
}


/* Delete an ARP mapping entry in the cache. */
void
arp_destructor(unsigned long paddr, int force)
{
  struct arp_table *apt;
  struct arp_table **lapt;
  unsigned long hash;

  DPRINTF((DBG_ARP, "ARP: destroy(%s)\n", in_ntoa(paddr)));

  /* We cannot destroy our own ARP entry. */
  if (chk_addr(paddr) == IS_MYADDR) {
	DPRINTF((DBG_ARP, "ARP: Destroying my own IP address %s !\n",
							in_ntoa(paddr)));
	return;
  }
  hash = htonl(paddr) & (ARP_TABLE_SIZE - 1);

  cli();
  lapt = &arp_tables[hash];
  while ((apt = *lapt) != NULL) {
	if (apt->ip == paddr) {
		if((apt->flags&ATF_PERM) && !force)
			return;
		*lapt = apt->next;
		if(apt->flags&ATF_PUBL)
			arp_proxies--;			
		kfree_s(apt, sizeof(struct arp_table));
		sti();
		return;
	}
	lapt = &apt->next;
  }
  sti();
}

/*
 *	Kill an entry - eg for ioctl()
 */

void arp_destroy(unsigned long paddr)
{	
	arp_destructor(paddr,1);
}

/*
 *	Delete a possibly invalid entry (see timer.c)
 */

void arp_destroy_maybe(unsigned long paddr)
{
	arp_destructor(paddr,0);
}

/* Create an ARP entry.  The caller should check for duplicates! */
static struct arp_table *
arp_create(unsigned long paddr, unsigned char *addr, int hlen, int htype)
{
  struct arp_table *apt;
  unsigned long hash;

  DPRINTF((DBG_ARP, "ARP: create(%s, ", in_ntoa(paddr)));
  DPRINTF((DBG_ARP, "%s, ", eth_print(addr)));
  DPRINTF((DBG_ARP, "%d, %d)\n", hlen, htype));

  apt = (struct arp_table *) kmalloc(sizeof(struct arp_table), GFP_ATOMIC);
  if (apt == NULL) {
	printk("ARP: no memory available for new ARP entry!\n");
	return(NULL);
  }

  /* Fill in the allocated ARP cache entry. */
  hash = htonl(paddr) & (ARP_TABLE_SIZE - 1);
  apt->ip = paddr;
  apt->hlen = hlen;
  apt->htype = htype;
  apt->flags = (ATF_INUSE | ATF_COM);		/* USED and COMPLETED entry */