ip.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

        /* Fill in the structure. */
	fp->offset = offset;
	fp->end = end;
	fp->len = end - offset;
	fp->skb = skb;
	fp->ptr = ptr;
 
	return(fp);
}
 
 
/*
 * Find the correct entry in the "incomplete datagrams" queue for
 * this IP datagram, and return the queue entry address if found.
 */
static struct ipq *ip_find(struct iphdr *iph)
{
	struct ipq *qp;
	struct ipq *qplast;
 
	cli();
	qplast = NULL;
	for(qp = ipqueue; qp != NULL; qplast = qp, qp = qp->next) 
	{
 		if (iph->id== qp->iph->id && iph->saddr == qp->iph->saddr &&
			iph->daddr == qp->iph->daddr && iph->protocol == qp->iph->protocol) 
		{
			del_timer(&qp->timer);	/* So it doesnt vanish on us. The timer will be reset anyway */
 			sti();
 			return(qp);
 		}
   	}
	sti();
	return(NULL);
}
 
 
/*
 * Remove an entry from the "incomplete datagrams" queue, either
 * because we completed, reassembled and processed it, or because
 * it timed out.
 */

static void ip_free(struct ipq *qp)
{
	struct ipfrag *fp;
	struct ipfrag *xp;

	/* Stop the timer for this entry. */
/*	printk("ip_free\n");*/
	del_timer(&qp->timer);

	/* Remove this entry from the "incomplete datagrams" queue. */
	cli();
	if (qp->prev == NULL) 
	{
	 	ipqueue = qp->next;
	 	if (ipqueue != NULL) 
	 		ipqueue->prev = NULL;
   	} 
   	else 
   	{
 		qp->prev->next = qp->next;
 		if (qp->next != NULL) 
 			qp->next->prev = qp->prev;
   	}
 
   	/* Release all fragment data. */
/*   	printk("ip_free: kill frag data\n");*/
   	fp = qp->fragments;
   	while (fp != NULL) 
   	{
 		xp = fp->next;
 		IS_SKB(fp->skb);
 		kfree_skb(fp->skb,FREE_READ);
 		kfree_s(fp, sizeof(struct ipfrag));
 		fp = xp;
   	}
   	
/*   	printk("ip_free: cleanup\n");*/
 
   	/* Release the MAC header. */
   	kfree_s(qp->mac, qp->maclen);
 
   	/* Release the IP header. */
   	kfree_s(qp->iph, qp->ihlen + 8);
 
   	/* Finally, release the queue descriptor itself. */
   	kfree_s(qp, sizeof(struct ipq));
/*   	printk("ip_free:done\n");*/
   	sti();
 }
 
 
 /* Oops- a fragment queue timed out.  Kill it and send an ICMP reply. */
 
static void ip_expire(unsigned long arg)
{
   	struct ipq *qp;
 
   	qp = (struct ipq *)arg;
   	DPRINTF((DBG_IP, "IP: queue_expire: fragment queue 0x%X timed out!\n", qp));
 
   	/* Send an ICMP "Fragment Reassembly Timeout" message. */
#if 0   	
   	icmp_send(qp->iph->ip_src.s_addr, ICMP_TIME_EXCEEDED,
 		    ICMP_EXC_FRAGTIME, qp->iph);
#endif 		 
 	if(qp->fragments!=NULL)
 		icmp_send(qp->fragments->skb,ICMP_TIME_EXCEEDED,
 				ICMP_EXC_FRAGTIME, qp->dev);
 
   	/* Nuke the fragment queue. */
	ip_free(qp);
}
 
 
/*
 * Add an entry to the 'ipq' queue for a newly received IP datagram.
 * We will (hopefully :-) receive all other fragments of this datagram
 * in time, so we just create a queue for this datagram, in which we
 * will insert the received fragments at their respective positions.
 */

static struct ipq *ip_create(struct sk_buff *skb, struct iphdr *iph, struct device *dev)
{
  	struct ipq *qp;
  	int maclen;
  	int ihlen;

  	qp = (struct ipq *) kmalloc(sizeof(struct ipq), GFP_ATOMIC);
  	if (qp == NULL) 
  	{
		printk("IP: create: no memory left !\n");
		return(NULL);
  	}
 	memset(qp, 0, sizeof(struct ipq));

  	/* Allocate memory for the MAC header. */
  	maclen = ((unsigned long) iph) - ((unsigned long) skb->data);
  	qp->mac = (unsigned char *) kmalloc(maclen, GFP_ATOMIC);
  	if (qp->mac == NULL) 
  	{
		printk("IP: create: no memory left !\n");
		kfree_s(qp, sizeof(struct ipq));
		return(NULL);
  	}

  	/* Allocate memory for the IP header (plus 8 octects for ICMP). */
  	ihlen = (iph->ihl * sizeof(unsigned long));
  	qp->iph = (struct iphdr *) kmalloc(ihlen + 8, GFP_ATOMIC);
  	if (qp->iph == NULL) 
  	{
		printk("IP: create: no memory left !\n");
		kfree_s(qp->mac, maclen);
		kfree_s(qp, sizeof(struct ipq));
		return(NULL);
  	}

  	/* Fill in the structure. */
  	memcpy(qp->mac, skb->data, maclen);
 	memcpy(qp->iph, iph, ihlen + 8);
  	qp->len = 0;
  	qp->ihlen = ihlen;
  	qp->maclen = maclen;
  	qp->fragments = NULL;
  	qp->dev = dev;
/*  	printk("Protocol = %d\n",qp->iph->protocol);*/
	
  	/* Start a timer for this entry. */
  	qp->timer.expires = IP_FRAG_TIME;		/* about 30 seconds	*/
  	qp->timer.data = (unsigned long) qp;		/* pointer to queue	*/
  	qp->timer.function = ip_expire;			/* expire function	*/
  	add_timer(&qp->timer);

  	/* Add this entry to the queue. */
  	qp->prev = NULL;
  	cli();
  	qp->next = ipqueue;
  	if (qp->next != NULL) 
  		qp->next->prev = qp;
  	ipqueue = qp;
  	sti();
  	return(qp);
}
 
 
 /* See if a fragment queue is complete. */
static int ip_done(struct ipq *qp)
{
	struct ipfrag *fp;
	int offset;
 
   	/* Only possible if we received the final fragment. */
   	if (qp->len == 0) 
   		return(0);
 
   	/* Check all fragment offsets to see if they connect. */
  	fp = qp->fragments;
   	offset = 0;
   	while (fp != NULL) 
   	{
 		if (fp->offset > offset) 
 			return(0);	/* fragment(s) missing */
 		offset = fp->end;
 		fp = fp->next;
   	}
 
   	/* All fragments are present. */
   	return(1);
 }
 
 
/* Build a new IP datagram from all its fragments. */
static struct sk_buff *ip_glue(struct ipq *qp)
{
	struct sk_buff *skb;
   	struct iphdr *iph;
   	struct ipfrag *fp;
   	unsigned char *ptr;
   	int count, len;
 
   	/* Allocate a new buffer for the datagram. */
   	len = sizeof(struct sk_buff)+qp->maclen + qp->ihlen + qp->len;
   	if ((skb = alloc_skb(len,GFP_ATOMIC)) == NULL) 
   	{
 		printk("IP: queue_glue: no memory for glueing queue 0x%X\n", (int) qp);
 		ip_free(qp);
 		return(NULL);
   	}
 
   	/* Fill in the basic details. */
   	skb->len = (len - qp->maclen);
   	skb->h.raw = skb->data;
   	skb->free = 1;
 
   	/* Copy the original MAC and IP headers into the new buffer. */
   	ptr = (unsigned char *) skb->h.raw;
   	memcpy(ptr, ((unsigned char *) qp->mac), qp->maclen);
/*   	printk("Copied %d bytes of mac header.\n",qp->maclen);*/
   	ptr += qp->maclen;
   	memcpy(ptr, ((unsigned char *) qp->iph), qp->ihlen);
/*   	printk("Copied %d byte of ip header.\n",qp->ihlen);*/
   	ptr += qp->ihlen;
   	skb->h.raw += qp->maclen;
   	
/*   	printk("Protocol = %d\n",skb->h.iph->protocol);*/
   	count = 0;
 
   	/* Copy the data portions of all fragments into the new buffer. */
   	fp = qp->fragments;
   	while(fp != NULL) 
   	{
   		if(count+fp->len>skb->len)
   		{
   			printk("Invalid fragment list: Fragment over size.\n");
   			ip_free(qp);
   			kfree_skb(skb,FREE_WRITE);
   			return NULL;
   		}
/*   		printk("Fragment %d size %d\n",fp->offset,fp->len);*/
 		memcpy((ptr + fp->offset), fp->ptr, fp->len);
 		count += fp->len;
 		fp = fp->next;
   	}
 
   	/* We glued together all fragments, so remove the queue entry. */
   	ip_free(qp);
 
   	/* Done with all fragments. Fixup the new IP header. */
   	iph = skb->h.iph;
   	iph->frag_off = 0;
   	iph->tot_len = htons((iph->ihl * sizeof(unsigned long)) + count);
   	skb->ip_hdr = iph;
   	return(skb);
}
 

/* Process an incoming IP datagram fragment. */
static struct sk_buff *ip_defrag(struct iphdr *iph, struct sk_buff *skb, struct device *dev)
{
	struct ipfrag *prev, *next;
	struct ipfrag *tfp;
	struct ipq *qp;
	struct sk_buff *skb2;
	unsigned char *ptr;
	int flags, offset;
	int i, ihl, end;

	/* Find the entry of this IP datagram in the "incomplete datagrams" queue. */
   	qp = ip_find(iph);
 
   	/* Is this a non-fragmented datagram? */
   	offset = ntohs(iph->frag_off);
   	flags = offset & ~IP_OFFSET;
   	offset &= IP_OFFSET;
   	if (((flags & IP_MF) == 0) && (offset == 0)) 
   	{
 		if (qp != NULL) 
 			ip_free(qp);	/* Huh? How could this exist?? */
 		return(skb);
   	}
   	offset <<= 3;		/* offset is in 8-byte chunks */
 
   	/*
    	 * If the queue already existed, keep restarting its timer as long
   	 * as we still are receiving fragments.  Otherwise, create a fresh
    	 * queue entry.
    	 */
   	if (qp != NULL) 
   	{
 		del_timer(&qp->timer);
 		qp->timer.expires = IP_FRAG_TIME;	/* about 30 seconds	*/
 		qp->timer.data = (unsigned long) qp;	/* pointer to queue	*/
 		qp->timer.function = ip_expire;		/* expire function	*/
 		add_timer(&qp->timer);
   	} 
   	else 
   	{
 		if ((qp = ip_create(skb, iph, dev)) == NULL) 
 			return(NULL);
   	}
 
   	/* Determine the position of this fragment. */
   	ihl = (iph->ihl * sizeof(unsigned long));
   	end = offset + ntohs(iph->tot_len) - ihl;
 
   	/* Point into the IP datagram 'data' part. */
   	ptr = skb->data + dev->hard_header_len + ihl;
 
   	/* Is this the final fragment? */
   	if ((flags & IP_MF) == 0) 
   		qp->len = end;
 
   	/*
   	 * Find out which fragments are in front and at the back of us
   	 * in the chain of fragments so far.  We must know where to put
   	 * this fragment, right?
   	 */
   	prev = NULL;
   	for(next = qp->fragments; next != NULL; next = next->next) 
   	{
 		if (next->offset > offset) 
 			break;	/* bingo! */
 		prev = next;
   	}	
 
   	/*
   	 * We found where to put this one.
   	 * Check for overlap with preceeding fragment, and, if needed,
   	 * align things so that any overlaps are eliminated.
   	 */
   	if (prev != NULL && offset < prev->end) 
   	{
 		i = prev->end - offset;
 		offset += i;	/* ptr into datagram */
 		ptr += i;	/* ptr into fragment data */
 		DPRINTF((DBG_IP, "IP: defrag: fixed low overlap %d bytes\n", i));
   	}	
 
   	/*
    	 * Look for overlap with succeeding segments.
    	 * If we can merge fragments, do it.
      	 */
   
   	for(; next != NULL; next = tfp) 
   	{
 		tfp = next->next;
 		if (next->offset >= end) 
 			break;		/* no overlaps at all */
 
 		i = end - next->offset;			/* overlap is 'i' bytes */
 		next->len -= i;				/* so reduce size of	*/
 		next->offset += i;			/* next fragment	*/
 		next->ptr += i;
 		
 		/* If we get a frag size of <= 0, remove it. */
 		if (next->len <= 0) 
 		{
 			DPRINTF((DBG_IP, "IP: defrag: removing frag 0x%X (len %d)\n",
 							next, next->len));
 			if (next->prev != NULL) 
 				next->prev->next = next->next;
 		  	else 
 		  		qp->fragments = next->next;
 		
 			if (tfp->next != NULL) 
 				next->next->prev = next->prev;
 			
 			kfree_s(next, sizeof(struct ipfrag));
 		}
 		DPRINTF((DBG_IP, "IP: defrag: fixed high overlap %d bytes\n", i));
   	}
 
   	/* Insert this fragment in the chain of fragments. */
   	tfp = NULL;
   	tfp = ip_frag_create(offset, end, skb, ptr);
   	tfp->prev = prev;
   	tfp->next = next;
   	if (prev != NULL) 
   		prev->next = tfp;
     	else 
     		qp->fragments = tfp;
   
   	if (next != NULL) 
   		next->prev = tfp;
 
   	/*
    	 * OK, so we inserted this new fragment into the chain.
    	 * Check if we now have a full IP datagram which we can
    	 * bump up to the IP layer...
    	 */
   
   	if (ip_done(qp)) 
   	{
 		skb2 = ip_glue(qp);		/* glue together the fragments */
 		return(skb2);
   	}
   	return(NULL);
 }
 
 
 /*
  * This IP datagram is too large to be sent in one piece.  Break it up into
  * smaller pieces (each of size equal to the MAC header plus IP header plus
  * a block of the data of the original IP data part) that will yet fit in a
  * single device frame, and queue such a frame for sending by calling the
  * ip_queue_xmit().  Note that this is recursion, and bad things will happen
  * if this function causes a loop...
  */
 void ip_fragment(struct sock *sk, struct sk_buff *skb, struct device *dev, int is_frag)
 {
   	struct iphdr *iph;
   	unsigned char *raw;
   	unsigned char *ptr;
   	struct sk_buff *skb2;
   	int left, mtu, hlen, len;
   	int offset;
 
   	/* Point into the IP datagram header. */
   	raw = skb->data;
   	iph = (struct iphdr *) (raw + dev->hard_header_len);

	skb->ip_hdr = iph;
	 	
   	/* Setup starting values. */
   	hlen = (iph->ihl * sizeof(unsigned long));
   	left = ntohs(iph->tot_len) - hlen;
   	hlen += dev->hard_header_len;
   	mtu = (dev->mtu - hlen);
   	ptr = (raw + hlen);
 	
   	DPRINTF((DBG_IP, "IP: Fragmentation Desired\n"));
   	DPRINTF((DBG_IP, "    DEV=%s, MTU=%d, LEN=%d SRC=%s",
 		dev->name, dev->mtu, left, in_ntoa(iph->saddr)));
   	DPRINTF((DBG_IP, " DST=%s\n", in_ntoa(iph->daddr)));
 
   	/* Check for any "DF" flag. */
   	if (ntohs(iph->frag_off) & IP_DF) 
   	{
 		DPRINTF((DBG_IP, "IP: Fragmentation Desired, but DF set !\n"));
 		DPRINTF((DBG_IP, "    DEV=%s, MTU=%d, LEN=%d SRC=%s",
 			dev->name, dev->mtu, left, in_ntoa(iph->saddr)));
 		DPRINTF((DBG_IP, " DST=%s\n", in_ntoa(iph->daddr)));
 
 		/*
 		 * FIXME:
 		 * We should send an ICMP warning message here!
 		 */
 		 
 		icmp_send(skb,ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, dev); 
 		return;
   	}
 
   	/* Fragment the datagram. */
	if (is_frag & 2)
	  offset = (ntohs(iph->frag_off) & 0x1fff) << 3;
	else
   	  offset = 0;
   	while(left > 0) 
   	{
 		len = left;
#ifdef OLD 		
 		if (len+8 > mtu) 
 			len = (dev->mtu - hlen - 8);
 		if ((left - len) >= 8) 
 		{
 			len /= 8;
 			len *= 8;
 		}
#else
		/* IF: it doesn't fit, use 'mtu' - the data space left */
		if (len > mtu)
			len = mtu;
		/* IF: we are not sending upto and including the packet end
		   then align the next start on an eight byte boundary */
		if (len < left)
		{
			len/=8;
			len*=8;
		}
#endif		 		
 		DPRINTF((DBG_IP,"IP: frag: creating fragment of %d bytes (%d total)\n",
 							len, len + hlen));
 
 		/* Allocate buffer. */
 		if ((skb2 = alloc_skb(sizeof(struct sk_buff) + len + hlen,GFP_ATOMIC)) == NULL) 
 		{
 			printk("IP: frag: no memory for new fragment!\n");
 			return;
 		}
 		skb2->arp = skb->arp;
 		skb2->free = skb->free;
 		skb2->len = len + hlen;
 		skb2->h.raw=(char *) skb2->data;
 
 		if (sk) 
 			sk->wmem_alloc += skb2->mem_len;
 
 		/* Copy the packet header into the new buffer. */
 		memcpy(skb2->h.raw, raw, hlen);
 
 		/* Copy a block of the IP datagram. */
 		memcpy(skb2->h.raw + hlen, ptr, len);
 		left -= len;

		skb2->h.raw+=dev->hard_header_len; 
 		/* Fill in the new header fields. */
 		iph = (struct iphdr *)(skb2->h.raw/*+dev->hard_header_len*/);
 		iph->frag_off = htons((offset >> 3));
 		/* Added AC : If we are fragmenting a fragment thats not the
 		   last fragment then keep MF on each bit */
 		if (left > 0 || (is_frag & 1)) 
 			iph->frag_off |= htons(IP_MF);
 		ptr += len;