icmp.c

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		if (ip_route_output(&rt, icmp_param.replyopts.faddr, saddr, RT_TOS(tos), 0))
			goto out;
	}

	if (!icmpv4_xrlim_allow(rt, type, code))
		goto ende;

	/* RFC says return as much as we can without exceeding 576 bytes. */

	room = rt->u.dst.pmtu;
	if (room > 576)
		room = 576;
	room -= sizeof(struct iphdr) + icmp_param.replyopts.optlen;
	room -= sizeof(struct icmphdr);

	icmp_param.data_len=skb_in->len-icmp_param.offset;
	if (icmp_param.data_len > room)
		icmp_param.data_len = room;
	icmp_param.head_len = sizeof(struct icmphdr);

	ip_build_xmit(icmp_socket->sk, icmp_glue_bits, &icmp_param, 
		icmp_param.data_len+sizeof(struct icmphdr),
		&ipc, rt, MSG_DONTWAIT);

ende:
	ip_rt_put(rt);
out:
	icmp_xmit_unlock();
}


/* 
 *	Handle ICMP_DEST_UNREACH, ICMP_TIME_EXCEED, and ICMP_QUENCH. 
 */

static void icmp_unreach(struct sk_buff *skb)
{
	struct iphdr *iph;
	struct icmphdr *icmph;
	int hash, protocol;
	struct inet_protocol *ipprot;
	struct sock *raw_sk;
	u32 info = 0;

	/*
	 *	Incomplete header ?
	 * 	Only checks for the IP header, there should be an
	 *	additional check for longer headers in upper levels.
	 */

	if (!pskb_may_pull(skb, sizeof(struct iphdr))) {
		ICMP_INC_STATS_BH(IcmpInErrors);
		return;
	}

	icmph = skb->h.icmph;
	iph = (struct iphdr *) skb->data;

	if (iph->ihl<5) {
		/* Mangled header, drop. */
		ICMP_INC_STATS_BH(IcmpInErrors);
		return;
	}

	if(icmph->type==ICMP_DEST_UNREACH) {
		switch(icmph->code & 15) {
			case ICMP_NET_UNREACH:
				break;
			case ICMP_HOST_UNREACH:
				break;
			case ICMP_PROT_UNREACH:
				break;
			case ICMP_PORT_UNREACH:
				break;
			case ICMP_FRAG_NEEDED:
				if (ipv4_config.no_pmtu_disc) {
					if (net_ratelimit())
						printk(KERN_INFO "ICMP: %u.%u.%u.%u: fragmentation needed and DF set.\n",
						       NIPQUAD(iph->daddr));
				} else {
					info = ip_rt_frag_needed(iph, ntohs(icmph->un.frag.mtu));
					if (!info) 
						goto out;
				}
				break;
			case ICMP_SR_FAILED:
				if (net_ratelimit())
					printk(KERN_INFO "ICMP: %u.%u.%u.%u: Source Route Failed.\n", NIPQUAD(iph->daddr));
				break;
			default:
				break;
		}
		if (icmph->code>NR_ICMP_UNREACH)
			goto out;
	} else if (icmph->type == ICMP_PARAMETERPROB) {
		info = ntohl(icmph->un.gateway)>>24;
	}

	/*
	 *	Throw it at our lower layers
	 *
	 *	RFC 1122: 3.2.2 MUST extract the protocol ID from the passed header.
	 *	RFC 1122: 3.2.2.1 MUST pass ICMP unreach messages to the transport layer.
	 *	RFC 1122: 3.2.2.2 MUST pass ICMP time expired messages to transport layer.
	 */

	/*
	 *	Check the other end isnt violating RFC 1122. Some routers send
	 *	bogus responses to broadcast frames. If you see this message
	 *	first check your netmask matches at both ends, if it does then
	 *	get the other vendor to fix their kit.
	 */

	if (!sysctl_icmp_ignore_bogus_error_responses)
	{
	
		if (inet_addr_type(iph->daddr) == RTN_BROADCAST)
		{
			if (net_ratelimit())
				printk(KERN_WARNING "%u.%u.%u.%u sent an invalid ICMP error to a broadcast.\n",
			       	NIPQUAD(skb->nh.iph->saddr));
			goto out;
		}
	}

	/* Checkin full IP header plus 8 bytes of protocol to
	 * avoid additional coding at protocol handlers.
	 */
	if (!pskb_may_pull(skb, iph->ihl*4+8))
		goto out;

	iph = (struct iphdr *) skb->data;
	protocol = iph->protocol;

	/*
	 *	Deliver ICMP message to raw sockets. Pretty useless feature?
	 */

	/* Note: See raw.c and net/raw.h, RAWV4_HTABLE_SIZE==MAX_INET_PROTOS */
	hash = protocol & (MAX_INET_PROTOS - 1);
	read_lock(&raw_v4_lock);
	if ((raw_sk = raw_v4_htable[hash]) != NULL) 
	{
		while ((raw_sk = __raw_v4_lookup(raw_sk, protocol, iph->daddr,
						 iph->saddr, skb->dev->ifindex)) != NULL) {
			raw_err(raw_sk, skb, info);
			raw_sk = raw_sk->next;
			iph = (struct iphdr *)skb->data;
		}
	}
	read_unlock(&raw_v4_lock);

	/*
	 *	This can't change while we are doing it. 
	 *	Callers have obtained BR_NETPROTO_LOCK so
	 *	we are OK.
	 */

	ipprot = (struct inet_protocol *) inet_protos[hash];
	while (ipprot) {
		struct inet_protocol *nextip;

		nextip = (struct inet_protocol *) ipprot->next;
	
		/* 
		 *	Pass it off to everyone who wants it. 
		 */

		/* RFC1122: OK. Passes appropriate ICMP errors to the */
		/* appropriate protocol layer (MUST), as per 3.2.2. */

		if (protocol == ipprot->protocol && ipprot->err_handler)
 			ipprot->err_handler(skb, info);

		ipprot = nextip;
  	}
out:;
}


/*
 *	Handle ICMP_REDIRECT. 
 */

static void icmp_redirect(struct sk_buff *skb)
{
	struct iphdr *iph;
	unsigned long ip;

	if (skb->len < sizeof(struct iphdr)) {
		ICMP_INC_STATS_BH(IcmpInErrors);
		return; 
	}

	/*
	 *	Get the copied header of the packet that caused the redirect
	 */
	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
		return;

	iph = (struct iphdr *) skb->data;
	ip = iph->daddr;

	switch (skb->h.icmph->code & 7) {
		case ICMP_REDIR_NET:
		case ICMP_REDIR_NETTOS:
			/*
			 *	As per RFC recommendations now handle it as
			 *	a host redirect.
			 */
			 
		case ICMP_REDIR_HOST:
		case ICMP_REDIR_HOSTTOS:
			ip_rt_redirect(skb->nh.iph->saddr, ip, skb->h.icmph->un.gateway, iph->saddr, iph->tos, skb->dev);
			break;
		default:
			break;
  	}
}

/*
 *	Handle ICMP_ECHO ("ping") requests. 
 *
 *	RFC 1122: 3.2.2.6 MUST have an echo server that answers ICMP echo requests.
 *	RFC 1122: 3.2.2.6 Data received in the ICMP_ECHO request MUST be included in the reply.
 *	RFC 1812: 4.3.3.6 SHOULD have a config option for silently ignoring echo requests, MUST have default=NOT.
 *	See also WRT handling of options once they are done and working.
 */

static void icmp_echo(struct sk_buff *skb)
{
	if (!sysctl_icmp_echo_ignore_all) {
		struct icmp_bxm icmp_param;

		icmp_param.data.icmph=*skb->h.icmph;
		icmp_param.data.icmph.type=ICMP_ECHOREPLY;
		icmp_param.skb=skb;
		icmp_param.offset=0;
		icmp_param.data_len=skb->len;
		icmp_param.head_len=sizeof(struct icmphdr);
		icmp_reply(&icmp_param, skb);
	}
}

/*
 *	Handle ICMP Timestamp requests. 
 *	RFC 1122: 3.2.2.8 MAY implement ICMP timestamp requests.
 *		  SHOULD be in the kernel for minimum random latency.
 *		  MUST be accurate to a few minutes.
 *		  MUST be updated at least at 15Hz.
 */
 
static void icmp_timestamp(struct sk_buff *skb)
{
	struct timeval tv;
	struct icmp_bxm icmp_param;
	
	/*
	 *	Too short.
	 */
	 
	if (skb->len < 4) {
		ICMP_INC_STATS_BH(IcmpInErrors);
		return;
	}

	/*
	 *	Fill in the current time as ms since midnight UT: 
	 */
	do_gettimeofday(&tv);
	icmp_param.data.times[1] = htonl((tv.tv_sec % 86400) * 1000 + tv.tv_usec / 1000);
	icmp_param.data.times[2] = icmp_param.data.times[1];
	if (skb_copy_bits(skb, 0, &icmp_param.data.times[0], 4))
		BUG();
	icmp_param.data.icmph=*skb->h.icmph;
	icmp_param.data.icmph.type=ICMP_TIMESTAMPREPLY;
	icmp_param.data.icmph.code=0;
	icmp_param.skb=skb;
	icmp_param.offset=0;
	icmp_param.data_len=0;
	icmp_param.head_len=sizeof(struct icmphdr)+12;
	icmp_reply(&icmp_param, skb);
}


/* 
 *	Handle ICMP_ADDRESS_MASK requests.  (RFC950)
 *
 * RFC1122 (3.2.2.9).  A host MUST only send replies to 
 * ADDRESS_MASK requests if it's been configured as an address mask 
 * agent.  Receiving a request doesn't constitute implicit permission to 
 * act as one. Of course, implementing this correctly requires (SHOULD) 
 * a way to turn the functionality on and off.  Another one for sysctl(), 
 * I guess. -- MS
 *
 * RFC1812 (4.3.3.9).	A router MUST implement it.
 *			A router SHOULD have switch turning it on/off.
 *		      	This switch MUST be ON by default.
 *
 * Gratuitous replies, zero-source replies are not implemented,
 * that complies with RFC. DO NOT implement them!!! All the idea
 * of broadcast addrmask replies as specified in RFC950 is broken.
 * The problem is that it is not uncommon to have several prefixes
 * on one physical interface. Moreover, addrmask agent can even be
 * not aware of existing another prefixes.
 * If source is zero, addrmask agent cannot choose correct prefix.
 * Gratuitous mask announcements suffer from the same problem.
 * RFC1812 explains it, but still allows to use ADDRMASK,
 * that is pretty silly. --ANK
 *
 * All these rules are so bizarre, that I removed kernel addrmask
 * support at all. It is wrong, it is obsolete, nobody uses it in
 * any case. --ANK
 *
 * Furthermore you can do it with a usermode address agent program
 * anyway...
 */

static void icmp_address(struct sk_buff *skb)
{
#if 0
	if (net_ratelimit())
		printk(KERN_DEBUG "a guy asks for address mask. Who is it?\n");
#endif		
}

/*
 * RFC1812 (4.3.3.9).	A router SHOULD listen all replies, and complain
 *			loudly if an inconsistency is found.
 */

static void icmp_address_reply(struct sk_buff *skb)
{
	struct rtable *rt = (struct rtable*)skb->dst;
	struct net_device *dev = skb->dev;
	struct in_device *in_dev;
	struct in_ifaddr *ifa;
	u32 mask;

	if (skb->len < 4 || !(rt->rt_flags&RTCF_DIRECTSRC))
		return;

	in_dev = in_dev_get(dev);
	if (!in_dev)
		return;
	read_lock(&in_dev->lock);
	if (in_dev->ifa_list &&
	    IN_DEV_LOG_MARTIANS(in_dev) &&
	    IN_DEV_FORWARD(in_dev)) {
		if (skb_copy_bits(skb, 0, &mask, 4))
			BUG();
		for (ifa=in_dev->ifa_list; ifa; ifa = ifa->ifa_next) {
			if (mask == ifa->ifa_mask && inet_ifa_match(rt->rt_src, ifa))
				break;
		}
		if (!ifa && net_ratelimit()) {
			printk(KERN_INFO "Wrong address mask %u.%u.%u.%u from %s/%u.%u.%u.%u\n",
			       NIPQUAD(mask), dev->name, NIPQUAD(rt->rt_src));
		}
	}
	read_unlock(&in_dev->lock);
	in_dev_put(in_dev);
}

static void icmp_discard(struct sk_buff *skb)
{
}

/* 
 *	Deal with incoming ICMP packets.
 */
 
int icmp_rcv(struct sk_buff *skb)
{
	struct icmphdr *icmph = skb->h.icmph;
	struct rtable *rt = (struct rtable*)skb->dst;

	ICMP_INC_STATS_BH(IcmpInMsgs);

	switch (skb->ip_summed) {
	case CHECKSUM_HW:
		if ((u16)csum_fold(skb->csum) == 0)
			break;
		NETDEBUG(if (net_ratelimit()) printk(KERN_DEBUG "icmp v4 hw csum failure\n"));
	case CHECKSUM_NONE:
		if ((u16)csum_fold(skb_checksum(skb, 0, skb->len, 0)))
			goto error;
	default:;
	}

	if (!pskb_pull(skb, sizeof(struct icmphdr)))
		goto error;

	/*
	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
	 *
	 *	RFC 1122: 3.2.2  Unknown ICMP messages types MUST be silently discarded.
	 */
	if (icmph->type > NR_ICMP_TYPES)
		goto error;


	/*
	 *	Parse the ICMP message 
	 */

 	if (rt->rt_flags&(RTCF_BROADCAST|RTCF_MULTICAST)) {
		/*
		 *	RFC 1122: 3.2.2.6 An ICMP_ECHO to broadcast MAY be
		 *	  silently ignored (we let user decide with a sysctl).
		 *	RFC 1122: 3.2.2.8 An ICMP_TIMESTAMP MAY be silently
		 *	  discarded if to broadcast/multicast.
		 */
		if (icmph->type == ICMP_ECHO &&
		    sysctl_icmp_echo_ignore_broadcasts) {
			goto error;
		}
		if (icmph->type != ICMP_ECHO &&
		    icmph->type != ICMP_TIMESTAMP &&
		    icmph->type != ICMP_ADDRESS &&
		    icmph->type != ICMP_ADDRESSREPLY) {
			goto error;
  		}
	}

	icmp_pointers[icmph->type].input[smp_processor_id()*2*sizeof(struct icmp_mib)/sizeof(unsigned long)]++;
	(icmp_pointers[icmph->type].handler)(skb);

drop:
	kfree_skb(skb);
	return 0;
error:
	ICMP_INC_STATS_BH(IcmpInErrors);
	goto drop;
}

/*
 *	This table is the definition of how we handle ICMP.
 */
 
static struct icmp_control icmp_pointers[NR_ICMP_TYPES+1] = {
/* ECHO REPLY (0) */
 { &icmp_statistics[0].IcmpOutEchoReps, &icmp_statistics[0].IcmpInEchoReps, icmp_discard, 0 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
/* DEST UNREACH (3) */
 { &icmp_statistics[0].IcmpOutDestUnreachs, &icmp_statistics[0].IcmpInDestUnreachs, icmp_unreach, 1 },
/* SOURCE QUENCH (4) */
 { &icmp_statistics[0].IcmpOutSrcQuenchs, &icmp_statistics[0].IcmpInSrcQuenchs, icmp_unreach, 1 },
/* REDIRECT (5) */
 { &icmp_statistics[0].IcmpOutRedirects, &icmp_statistics[0].IcmpInRedirects, icmp_redirect, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
/* ECHO (8) */
 { &icmp_statistics[0].IcmpOutEchos, &icmp_statistics[0].IcmpInEchos, icmp_echo, 0 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
 { &icmp_statistics[0].dummy, &icmp_statistics[0].IcmpInErrors, icmp_discard, 1 },
/* TIME EXCEEDED (11) */
 { &icmp_statistics[0].IcmpOutTimeExcds, &icmp_statistics[0].IcmpInTimeExcds, icmp_unreach, 1 },
/* PARAMETER PROBLEM (12) */
 { &icmp_statistics[0].IcmpOutParmProbs, &icmp_statistics[0].IcmpInParmProbs, icmp_unreach, 1 },
/* TIMESTAMP (13) */
 { &icmp_statistics[0].IcmpOutTimestamps, &icmp_statistics[0].IcmpInTimestamps, icmp_timestamp, 0  },
/* TIMESTAMP REPLY (14) */
 { &icmp_statistics[0].IcmpOutTimestampReps, &icmp_statistics[0].IcmpInTimestampReps, icmp_discard, 0 },
/* INFO (15) */
 { &icmp_statistics[0].dummy, &icmp_statistics[0].dummy, icmp_discard, 0 },
/* INFO REPLY (16) */
 { &icmp_statistics[0].dummy, &icmp_statistics[0].dummy, icmp_discard, 0 },
/* ADDR MASK (17) */
 { &icmp_statistics[0].IcmpOutAddrMasks, &icmp_statistics[0].IcmpInAddrMasks, icmp_address, 0  },
/* ADDR MASK REPLY (18) */
 { &icmp_statistics[0].IcmpOutAddrMaskReps, &icmp_statistics[0].IcmpInAddrMaskReps, icmp_address_reply, 0 }
};

void __init icmp_init(struct net_proto_family *ops)
{
	int err;

	icmp_inode.i_mode = S_IFSOCK;
	icmp_inode.i_sock = 1;
	icmp_inode.i_uid = 0;
	icmp_inode.i_gid = 0;
	init_waitqueue_head(&icmp_inode.i_wait);
	init_waitqueue_head(&icmp_inode.u.socket_i.wait);

	icmp_socket->inode = &icmp_inode;
	icmp_socket->state = SS_UNCONNECTED;
	icmp_socket->type=SOCK_RAW;

	if ((err=ops->create(icmp_socket, IPPROTO_ICMP))<0)
		panic("Failed to create the ICMP control socket.\n");
	icmp_socket->sk->allocation=GFP_ATOMIC;
	icmp_socket->sk->sndbuf = SK_WMEM_MAX*2;
	icmp_socket->sk->protinfo.af_inet.ttl = MAXTTL;
	icmp_socket->sk->protinfo.af_inet.pmtudisc = IP_PMTUDISC_DONT;

	/* Unhash it so that IP input processing does not even
	 * see it, we do not wish this socket to see incoming
	 * packets.
	 */
	icmp_socket->sk->prot->unhash(icmp_socket->sk);
}