xref: /openbmc/linux/net/dccp/ipv4.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
1 /*
2  *  net/dccp/ipv4.c
3  *
4  *  An implementation of the DCCP protocol
5  *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
6  *
7  *	This program is free software; you can redistribute it and/or
8  *	modify it under the terms of the GNU General Public License
9  *	as published by the Free Software Foundation; either version
10  *	2 of the License, or (at your option) any later version.
11  */
12 
13 #include <linux/dccp.h>
14 #include <linux/icmp.h>
15 #include <linux/module.h>
16 #include <linux/skbuff.h>
17 #include <linux/random.h>
18 
19 #include <net/icmp.h>
20 #include <net/inet_common.h>
21 #include <net/inet_hashtables.h>
22 #include <net/inet_sock.h>
23 #include <net/protocol.h>
24 #include <net/sock.h>
25 #include <net/timewait_sock.h>
26 #include <net/tcp_states.h>
27 #include <net/xfrm.h>
28 
29 #include "ackvec.h"
30 #include "ccid.h"
31 #include "dccp.h"
32 #include "feat.h"
33 
34 /*
35  * This is the global socket data structure used for responding to
36  * the Out-of-the-blue (OOTB) packets. A control sock will be created
37  * for this socket at the initialization time.
38  */
39 static struct socket *dccp_v4_ctl_socket;
40 
41 static int dccp_v4_get_port(struct sock *sk, const unsigned short snum)
42 {
43 	return inet_csk_get_port(&dccp_hashinfo, sk, snum,
44 				 inet_csk_bind_conflict);
45 }
46 
47 int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
48 {
49 	struct inet_sock *inet = inet_sk(sk);
50 	struct dccp_sock *dp = dccp_sk(sk);
51 	const struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
52 	struct rtable *rt;
53 	__be32 daddr, nexthop;
54 	int tmp;
55 	int err;
56 
57 	dp->dccps_role = DCCP_ROLE_CLIENT;
58 
59 	if (addr_len < sizeof(struct sockaddr_in))
60 		return -EINVAL;
61 
62 	if (usin->sin_family != AF_INET)
63 		return -EAFNOSUPPORT;
64 
65 	nexthop = daddr = usin->sin_addr.s_addr;
66 	if (inet->opt != NULL && inet->opt->srr) {
67 		if (daddr == 0)
68 			return -EINVAL;
69 		nexthop = inet->opt->faddr;
70 	}
71 
72 	tmp = ip_route_connect(&rt, nexthop, inet->saddr,
73 			       RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
74 			       IPPROTO_DCCP,
75 			       inet->sport, usin->sin_port, sk, 1);
76 	if (tmp < 0)
77 		return tmp;
78 
79 	if (rt->rt_flags & (RTCF_MULTICAST | RTCF_BROADCAST)) {
80 		ip_rt_put(rt);
81 		return -ENETUNREACH;
82 	}
83 
84 	if (inet->opt == NULL || !inet->opt->srr)
85 		daddr = rt->rt_dst;
86 
87 	if (inet->saddr == 0)
88 		inet->saddr = rt->rt_src;
89 	inet->rcv_saddr = inet->saddr;
90 
91 	inet->dport = usin->sin_port;
92 	inet->daddr = daddr;
93 
94 	inet_csk(sk)->icsk_ext_hdr_len = 0;
95 	if (inet->opt != NULL)
96 		inet_csk(sk)->icsk_ext_hdr_len = inet->opt->optlen;
97 	/*
98 	 * Socket identity is still unknown (sport may be zero).
99 	 * However we set state to DCCP_REQUESTING and not releasing socket
100 	 * lock select source port, enter ourselves into the hash tables and
101 	 * complete initialization after this.
102 	 */
103 	dccp_set_state(sk, DCCP_REQUESTING);
104 	err = inet_hash_connect(&dccp_death_row, sk);
105 	if (err != 0)
106 		goto failure;
107 
108 	err = ip_route_newports(&rt, IPPROTO_DCCP, inet->sport, inet->dport,
109 				sk);
110 	if (err != 0)
111 		goto failure;
112 
113 	/* OK, now commit destination to socket.  */
114 	sk_setup_caps(sk, &rt->u.dst);
115 
116 	dp->dccps_iss = secure_dccp_sequence_number(inet->saddr, inet->daddr,
117 						    inet->sport, inet->dport);
118 	inet->id = dp->dccps_iss ^ jiffies;
119 
120 	err = dccp_connect(sk);
121 	rt = NULL;
122 	if (err != 0)
123 		goto failure;
124 out:
125 	return err;
126 failure:
127 	/*
128 	 * This unhashes the socket and releases the local port, if necessary.
129 	 */
130 	dccp_set_state(sk, DCCP_CLOSED);
131 	ip_rt_put(rt);
132 	sk->sk_route_caps = 0;
133 	inet->dport = 0;
134 	goto out;
135 }
136 
137 EXPORT_SYMBOL_GPL(dccp_v4_connect);
138 
139 /*
140  * This routine does path mtu discovery as defined in RFC1191.
141  */
142 static inline void dccp_do_pmtu_discovery(struct sock *sk,
143 					  const struct iphdr *iph,
144 					  u32 mtu)
145 {
146 	struct dst_entry *dst;
147 	const struct inet_sock *inet = inet_sk(sk);
148 	const struct dccp_sock *dp = dccp_sk(sk);
149 
150 	/* We are not interested in DCCP_LISTEN and request_socks (RESPONSEs
151 	 * send out by Linux are always < 576bytes so they should go through
152 	 * unfragmented).
153 	 */
154 	if (sk->sk_state == DCCP_LISTEN)
155 		return;
156 
157 	/* We don't check in the destentry if pmtu discovery is forbidden
158 	 * on this route. We just assume that no packet_to_big packets
159 	 * are send back when pmtu discovery is not active.
160 	 * There is a small race when the user changes this flag in the
161 	 * route, but I think that's acceptable.
162 	 */
163 	if ((dst = __sk_dst_check(sk, 0)) == NULL)
164 		return;
165 
166 	dst->ops->update_pmtu(dst, mtu);
167 
168 	/* Something is about to be wrong... Remember soft error
169 	 * for the case, if this connection will not able to recover.
170 	 */
171 	if (mtu < dst_mtu(dst) && ip_dont_fragment(sk, dst))
172 		sk->sk_err_soft = EMSGSIZE;
173 
174 	mtu = dst_mtu(dst);
175 
176 	if (inet->pmtudisc != IP_PMTUDISC_DONT &&
177 	    inet_csk(sk)->icsk_pmtu_cookie > mtu) {
178 		dccp_sync_mss(sk, mtu);
179 
180 		/*
181 		 * From RFC 4340, sec. 14.1:
182 		 *
183 		 *	DCCP-Sync packets are the best choice for upward
184 		 *	probing, since DCCP-Sync probes do not risk application
185 		 *	data loss.
186 		 */
187 		dccp_send_sync(sk, dp->dccps_gsr, DCCP_PKT_SYNC);
188 	} /* else let the usual retransmit timer handle it */
189 }
190 
191 /*
192  * This routine is called by the ICMP module when it gets some sort of error
193  * condition. If err < 0 then the socket should be closed and the error
194  * returned to the user. If err > 0 it's just the icmp type << 8 | icmp code.
195  * After adjustment header points to the first 8 bytes of the tcp header. We
196  * need to find the appropriate port.
197  *
198  * The locking strategy used here is very "optimistic". When someone else
199  * accesses the socket the ICMP is just dropped and for some paths there is no
200  * check at all. A more general error queue to queue errors for later handling
201  * is probably better.
202  */
203 static void dccp_v4_err(struct sk_buff *skb, u32 info)
204 {
205 	const struct iphdr *iph = (struct iphdr *)skb->data;
206 	const struct dccp_hdr *dh = (struct dccp_hdr *)(skb->data +
207 							(iph->ihl << 2));
208 	struct dccp_sock *dp;
209 	struct inet_sock *inet;
210 	const int type = icmp_hdr(skb)->type;
211 	const int code = icmp_hdr(skb)->code;
212 	struct sock *sk;
213 	__u64 seq;
214 	int err;
215 
216 	if (skb->len < (iph->ihl << 2) + 8) {
217 		ICMP_INC_STATS_BH(ICMP_MIB_INERRORS);
218 		return;
219 	}
220 
221 	sk = inet_lookup(&dccp_hashinfo, iph->daddr, dh->dccph_dport,
222 			 iph->saddr, dh->dccph_sport, inet_iif(skb));
223 	if (sk == NULL) {
224 		ICMP_INC_STATS_BH(ICMP_MIB_INERRORS);
225 		return;
226 	}
227 
228 	if (sk->sk_state == DCCP_TIME_WAIT) {
229 		inet_twsk_put(inet_twsk(sk));
230 		return;
231 	}
232 
233 	bh_lock_sock(sk);
234 	/* If too many ICMPs get dropped on busy
235 	 * servers this needs to be solved differently.
236 	 */
237 	if (sock_owned_by_user(sk))
238 		NET_INC_STATS_BH(LINUX_MIB_LOCKDROPPEDICMPS);
239 
240 	if (sk->sk_state == DCCP_CLOSED)
241 		goto out;
242 
243 	dp = dccp_sk(sk);
244 	seq = dccp_hdr_seq(skb);
245 	if (sk->sk_state != DCCP_LISTEN &&
246 	    !between48(seq, dp->dccps_swl, dp->dccps_swh)) {
247 		NET_INC_STATS_BH(LINUX_MIB_OUTOFWINDOWICMPS);
248 		goto out;
249 	}
250 
251 	switch (type) {
252 	case ICMP_SOURCE_QUENCH:
253 		/* Just silently ignore these. */
254 		goto out;
255 	case ICMP_PARAMETERPROB:
256 		err = EPROTO;
257 		break;
258 	case ICMP_DEST_UNREACH:
259 		if (code > NR_ICMP_UNREACH)
260 			goto out;
261 
262 		if (code == ICMP_FRAG_NEEDED) { /* PMTU discovery (RFC1191) */
263 			if (!sock_owned_by_user(sk))
264 				dccp_do_pmtu_discovery(sk, iph, info);
265 			goto out;
266 		}
267 
268 		err = icmp_err_convert[code].errno;
269 		break;
270 	case ICMP_TIME_EXCEEDED:
271 		err = EHOSTUNREACH;
272 		break;
273 	default:
274 		goto out;
275 	}
276 
277 	switch (sk->sk_state) {
278 		struct request_sock *req , **prev;
279 	case DCCP_LISTEN:
280 		if (sock_owned_by_user(sk))
281 			goto out;
282 		req = inet_csk_search_req(sk, &prev, dh->dccph_dport,
283 					  iph->daddr, iph->saddr);
284 		if (!req)
285 			goto out;
286 
287 		/*
288 		 * ICMPs are not backlogged, hence we cannot get an established
289 		 * socket here.
290 		 */
291 		BUG_TRAP(!req->sk);
292 
293 		if (seq != dccp_rsk(req)->dreq_iss) {
294 			NET_INC_STATS_BH(LINUX_MIB_OUTOFWINDOWICMPS);
295 			goto out;
296 		}
297 		/*
298 		 * Still in RESPOND, just remove it silently.
299 		 * There is no good way to pass the error to the newly
300 		 * created socket, and POSIX does not want network
301 		 * errors returned from accept().
302 		 */
303 		inet_csk_reqsk_queue_drop(sk, req, prev);
304 		goto out;
305 
306 	case DCCP_REQUESTING:
307 	case DCCP_RESPOND:
308 		if (!sock_owned_by_user(sk)) {
309 			DCCP_INC_STATS_BH(DCCP_MIB_ATTEMPTFAILS);
310 			sk->sk_err = err;
311 
312 			sk->sk_error_report(sk);
313 
314 			dccp_done(sk);
315 		} else
316 			sk->sk_err_soft = err;
317 		goto out;
318 	}
319 
320 	/* If we've already connected we will keep trying
321 	 * until we time out, or the user gives up.
322 	 *
323 	 * rfc1122 4.2.3.9 allows to consider as hard errors
324 	 * only PROTO_UNREACH and PORT_UNREACH (well, FRAG_FAILED too,
325 	 * but it is obsoleted by pmtu discovery).
326 	 *
327 	 * Note, that in modern internet, where routing is unreliable
328 	 * and in each dark corner broken firewalls sit, sending random
329 	 * errors ordered by their masters even this two messages finally lose
330 	 * their original sense (even Linux sends invalid PORT_UNREACHs)
331 	 *
332 	 * Now we are in compliance with RFCs.
333 	 *							--ANK (980905)
334 	 */
335 
336 	inet = inet_sk(sk);
337 	if (!sock_owned_by_user(sk) && inet->recverr) {
338 		sk->sk_err = err;
339 		sk->sk_error_report(sk);
340 	} else /* Only an error on timeout */
341 		sk->sk_err_soft = err;
342 out:
343 	bh_unlock_sock(sk);
344 	sock_put(sk);
345 }
346 
347 static inline __sum16 dccp_v4_csum_finish(struct sk_buff *skb,
348 				      __be32 src, __be32 dst)
349 {
350 	return csum_tcpudp_magic(src, dst, skb->len, IPPROTO_DCCP, skb->csum);
351 }
352 
353 void dccp_v4_send_check(struct sock *sk, int unused, struct sk_buff *skb)
354 {
355 	const struct inet_sock *inet = inet_sk(sk);
356 	struct dccp_hdr *dh = dccp_hdr(skb);
357 
358 	dccp_csum_outgoing(skb);
359 	dh->dccph_checksum = dccp_v4_csum_finish(skb, inet->saddr, inet->daddr);
360 }
361 
362 EXPORT_SYMBOL_GPL(dccp_v4_send_check);
363 
364 static inline u64 dccp_v4_init_sequence(const struct sk_buff *skb)
365 {
366 	return secure_dccp_sequence_number(ip_hdr(skb)->daddr,
367 					   ip_hdr(skb)->saddr,
368 					   dccp_hdr(skb)->dccph_dport,
369 					   dccp_hdr(skb)->dccph_sport);
370 }
371 
372 /*
373  * The three way handshake has completed - we got a valid ACK or DATAACK -
374  * now create the new socket.
375  *
376  * This is the equivalent of TCP's tcp_v4_syn_recv_sock
377  */
378 struct sock *dccp_v4_request_recv_sock(struct sock *sk, struct sk_buff *skb,
379 				       struct request_sock *req,
380 				       struct dst_entry *dst)
381 {
382 	struct inet_request_sock *ireq;
383 	struct inet_sock *newinet;
384 	struct dccp_sock *newdp;
385 	struct sock *newsk;
386 
387 	if (sk_acceptq_is_full(sk))
388 		goto exit_overflow;
389 
390 	if (dst == NULL && (dst = inet_csk_route_req(sk, req)) == NULL)
391 		goto exit;
392 
393 	newsk = dccp_create_openreq_child(sk, req, skb);
394 	if (newsk == NULL)
395 		goto exit;
396 
397 	sk_setup_caps(newsk, dst);
398 
399 	newdp		   = dccp_sk(newsk);
400 	newinet		   = inet_sk(newsk);
401 	ireq		   = inet_rsk(req);
402 	newinet->daddr	   = ireq->rmt_addr;
403 	newinet->rcv_saddr = ireq->loc_addr;
404 	newinet->saddr	   = ireq->loc_addr;
405 	newinet->opt	   = ireq->opt;
406 	ireq->opt	   = NULL;
407 	newinet->mc_index  = inet_iif(skb);
408 	newinet->mc_ttl	   = ip_hdr(skb)->ttl;
409 	newinet->id	   = jiffies;
410 
411 	dccp_sync_mss(newsk, dst_mtu(dst));
412 
413 	__inet_hash(&dccp_hashinfo, newsk, 0);
414 	__inet_inherit_port(&dccp_hashinfo, sk, newsk);
415 
416 	return newsk;
417 
418 exit_overflow:
419 	NET_INC_STATS_BH(LINUX_MIB_LISTENOVERFLOWS);
420 exit:
421 	NET_INC_STATS_BH(LINUX_MIB_LISTENDROPS);
422 	dst_release(dst);
423 	return NULL;
424 }
425 
426 EXPORT_SYMBOL_GPL(dccp_v4_request_recv_sock);
427 
428 static struct sock *dccp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
429 {
430 	const struct dccp_hdr *dh = dccp_hdr(skb);
431 	const struct iphdr *iph = ip_hdr(skb);
432 	struct sock *nsk;
433 	struct request_sock **prev;
434 	/* Find possible connection requests. */
435 	struct request_sock *req = inet_csk_search_req(sk, &prev,
436 						       dh->dccph_sport,
437 						       iph->saddr, iph->daddr);
438 	if (req != NULL)
439 		return dccp_check_req(sk, skb, req, prev);
440 
441 	nsk = inet_lookup_established(&dccp_hashinfo,
442 				      iph->saddr, dh->dccph_sport,
443 				      iph->daddr, dh->dccph_dport,
444 				      inet_iif(skb));
445 	if (nsk != NULL) {
446 		if (nsk->sk_state != DCCP_TIME_WAIT) {
447 			bh_lock_sock(nsk);
448 			return nsk;
449 		}
450 		inet_twsk_put(inet_twsk(nsk));
451 		return NULL;
452 	}
453 
454 	return sk;
455 }
456 
457 static struct dst_entry* dccp_v4_route_skb(struct sock *sk,
458 					   struct sk_buff *skb)
459 {
460 	struct rtable *rt;
461 	struct flowi fl = { .oif = ((struct rtable *)skb->dst)->rt_iif,
462 			    .nl_u = { .ip4_u =
463 				      { .daddr = ip_hdr(skb)->saddr,
464 					.saddr = ip_hdr(skb)->daddr,
465 					.tos = RT_CONN_FLAGS(sk) } },
466 			    .proto = sk->sk_protocol,
467 			    .uli_u = { .ports =
468 				       { .sport = dccp_hdr(skb)->dccph_dport,
469 					 .dport = dccp_hdr(skb)->dccph_sport }
470 				     }
471 			  };
472 
473 	security_skb_classify_flow(skb, &fl);
474 	if (ip_route_output_flow(&rt, &fl, sk, 0)) {
475 		IP_INC_STATS_BH(IPSTATS_MIB_OUTNOROUTES);
476 		return NULL;
477 	}
478 
479 	return &rt->u.dst;
480 }
481 
482 static int dccp_v4_send_response(struct sock *sk, struct request_sock *req,
483 				 struct dst_entry *dst)
484 {
485 	int err = -1;
486 	struct sk_buff *skb;
487 
488 	/* First, grab a route. */
489 
490 	if (dst == NULL && (dst = inet_csk_route_req(sk, req)) == NULL)
491 		goto out;
492 
493 	skb = dccp_make_response(sk, dst, req);
494 	if (skb != NULL) {
495 		const struct inet_request_sock *ireq = inet_rsk(req);
496 		struct dccp_hdr *dh = dccp_hdr(skb);
497 
498 		dh->dccph_checksum = dccp_v4_csum_finish(skb, ireq->loc_addr,
499 							      ireq->rmt_addr);
500 		memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
501 		err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
502 					    ireq->rmt_addr,
503 					    ireq->opt);
504 		err = net_xmit_eval(err);
505 	}
506 
507 out:
508 	dst_release(dst);
509 	return err;
510 }
511 
512 static void dccp_v4_ctl_send_reset(struct sock *sk, struct sk_buff *rxskb)
513 {
514 	int err;
515 	struct dccp_hdr *rxdh = dccp_hdr(rxskb), *dh;
516 	const struct iphdr *rxiph;
517 	const int dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
518 				       sizeof(struct dccp_hdr_ext) +
519 				       sizeof(struct dccp_hdr_reset);
520 	struct sk_buff *skb;
521 	struct dst_entry *dst;
522 	u64 seqno = 0;
523 
524 	/* Never send a reset in response to a reset. */
525 	if (rxdh->dccph_type == DCCP_PKT_RESET)
526 		return;
527 
528 	if (((struct rtable *)rxskb->dst)->rt_type != RTN_LOCAL)
529 		return;
530 
531 	dst = dccp_v4_route_skb(dccp_v4_ctl_socket->sk, rxskb);
532 	if (dst == NULL)
533 		return;
534 
535 	skb = alloc_skb(dccp_v4_ctl_socket->sk->sk_prot->max_header,
536 			GFP_ATOMIC);
537 	if (skb == NULL)
538 		goto out;
539 
540 	/* Reserve space for headers. */
541 	skb_reserve(skb, dccp_v4_ctl_socket->sk->sk_prot->max_header);
542 	skb->dst = dst_clone(dst);
543 
544 	dh = dccp_zeroed_hdr(skb, dccp_hdr_reset_len);
545 
546 	/* Build DCCP header and checksum it. */
547 	dh->dccph_type	   = DCCP_PKT_RESET;
548 	dh->dccph_sport	   = rxdh->dccph_dport;
549 	dh->dccph_dport	   = rxdh->dccph_sport;
550 	dh->dccph_doff	   = dccp_hdr_reset_len / 4;
551 	dh->dccph_x	   = 1;
552 	dccp_hdr_reset(skb)->dccph_reset_code =
553 				DCCP_SKB_CB(rxskb)->dccpd_reset_code;
554 
555 	/* See "8.3.1. Abnormal Termination" in RFC 4340 */
556 	if (DCCP_SKB_CB(rxskb)->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
557 		dccp_set_seqno(&seqno, DCCP_SKB_CB(rxskb)->dccpd_ack_seq + 1);
558 
559 	dccp_hdr_set_seq(dh, seqno);
560 	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), DCCP_SKB_CB(rxskb)->dccpd_seq);
561 
562 	dccp_csum_outgoing(skb);
563 	rxiph = ip_hdr(rxskb);
564 	dh->dccph_checksum = dccp_v4_csum_finish(skb, rxiph->saddr,
565 						 rxiph->daddr);
566 
567 	bh_lock_sock(dccp_v4_ctl_socket->sk);
568 	err = ip_build_and_send_pkt(skb, dccp_v4_ctl_socket->sk,
569 				    rxiph->daddr, rxiph->saddr, NULL);
570 	bh_unlock_sock(dccp_v4_ctl_socket->sk);
571 
572 	if (net_xmit_eval(err) == 0) {
573 		DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);
574 		DCCP_INC_STATS_BH(DCCP_MIB_OUTRSTS);
575 	}
576 out:
577 	 dst_release(dst);
578 }
579 
580 static void dccp_v4_reqsk_destructor(struct request_sock *req)
581 {
582 	kfree(inet_rsk(req)->opt);
583 }
584 
585 static struct request_sock_ops dccp_request_sock_ops __read_mostly = {
586 	.family		= PF_INET,
587 	.obj_size	= sizeof(struct dccp_request_sock),
588 	.rtx_syn_ack	= dccp_v4_send_response,
589 	.send_ack	= dccp_reqsk_send_ack,
590 	.destructor	= dccp_v4_reqsk_destructor,
591 	.send_reset	= dccp_v4_ctl_send_reset,
592 };
593 
594 int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
595 {
596 	struct inet_request_sock *ireq;
597 	struct request_sock *req;
598 	struct dccp_request_sock *dreq;
599 	const __be32 service = dccp_hdr_request(skb)->dccph_req_service;
600 	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
601 	__u8 reset_code = DCCP_RESET_CODE_TOO_BUSY;
602 
603 	/* Never answer to DCCP_PKT_REQUESTs send to broadcast or multicast */
604 	if (((struct rtable *)skb->dst)->rt_flags &
605 	    (RTCF_BROADCAST | RTCF_MULTICAST)) {
606 		reset_code = DCCP_RESET_CODE_NO_CONNECTION;
607 		goto drop;
608 	}
609 
610 	if (dccp_bad_service_code(sk, service)) {
611 		reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
612 		goto drop;
613 	}
614 	/*
615 	 * TW buckets are converted to open requests without
616 	 * limitations, they conserve resources and peer is
617 	 * evidently real one.
618 	 */
619 	if (inet_csk_reqsk_queue_is_full(sk))
620 		goto drop;
621 
622 	/*
623 	 * Accept backlog is full. If we have already queued enough
624 	 * of warm entries in syn queue, drop request. It is better than
625 	 * clogging syn queue with openreqs with exponentially increasing
626 	 * timeout.
627 	 */
628 	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1)
629 		goto drop;
630 
631 	req = reqsk_alloc(&dccp_request_sock_ops);
632 	if (req == NULL)
633 		goto drop;
634 
635 	if (dccp_parse_options(sk, skb))
636 		goto drop_and_free;
637 
638 	dccp_reqsk_init(req, skb);
639 
640 	if (security_inet_conn_request(sk, skb, req))
641 		goto drop_and_free;
642 
643 	ireq = inet_rsk(req);
644 	ireq->loc_addr = ip_hdr(skb)->daddr;
645 	ireq->rmt_addr = ip_hdr(skb)->saddr;
646 	ireq->opt	= NULL;
647 
648 	/*
649 	 * Step 3: Process LISTEN state
650 	 *
651 	 * Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
652 	 *
653 	 * In fact we defer setting S.GSR, S.SWL, S.SWH to
654 	 * dccp_create_openreq_child.
655 	 */
656 	dreq = dccp_rsk(req);
657 	dreq->dreq_isr	   = dcb->dccpd_seq;
658 	dreq->dreq_iss	   = dccp_v4_init_sequence(skb);
659 	dreq->dreq_service = service;
660 
661 	if (dccp_v4_send_response(sk, req, NULL))
662 		goto drop_and_free;
663 
664 	inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT);
665 	return 0;
666 
667 drop_and_free:
668 	reqsk_free(req);
669 drop:
670 	DCCP_INC_STATS_BH(DCCP_MIB_ATTEMPTFAILS);
671 	dcb->dccpd_reset_code = reset_code;
672 	return -1;
673 }
674 
675 EXPORT_SYMBOL_GPL(dccp_v4_conn_request);
676 
677 int dccp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
678 {
679 	struct dccp_hdr *dh = dccp_hdr(skb);
680 
681 	if (sk->sk_state == DCCP_OPEN) { /* Fast path */
682 		if (dccp_rcv_established(sk, skb, dh, skb->len))
683 			goto reset;
684 		return 0;
685 	}
686 
687 	/*
688 	 *  Step 3: Process LISTEN state
689 	 *	 If P.type == Request or P contains a valid Init Cookie option,
690 	 *	      (* Must scan the packet's options to check for Init
691 	 *		 Cookies.  Only Init Cookies are processed here,
692 	 *		 however; other options are processed in Step 8.  This
693 	 *		 scan need only be performed if the endpoint uses Init
694 	 *		 Cookies *)
695 	 *	      (* Generate a new socket and switch to that socket *)
696 	 *	      Set S := new socket for this port pair
697 	 *	      S.state = RESPOND
698 	 *	      Choose S.ISS (initial seqno) or set from Init Cookies
699 	 *	      Initialize S.GAR := S.ISS
700 	 *	      Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookies
701 	 *	      Continue with S.state == RESPOND
702 	 *	      (* A Response packet will be generated in Step 11 *)
703 	 *	 Otherwise,
704 	 *	      Generate Reset(No Connection) unless P.type == Reset
705 	 *	      Drop packet and return
706 	 *
707 	 * NOTE: the check for the packet types is done in
708 	 *	 dccp_rcv_state_process
709 	 */
710 	if (sk->sk_state == DCCP_LISTEN) {
711 		struct sock *nsk = dccp_v4_hnd_req(sk, skb);
712 
713 		if (nsk == NULL)
714 			goto discard;
715 
716 		if (nsk != sk) {
717 			if (dccp_child_process(sk, nsk, skb))
718 				goto reset;
719 			return 0;
720 		}
721 	}
722 
723 	if (dccp_rcv_state_process(sk, skb, dh, skb->len))
724 		goto reset;
725 	return 0;
726 
727 reset:
728 	dccp_v4_ctl_send_reset(sk, skb);
729 discard:
730 	kfree_skb(skb);
731 	return 0;
732 }
733 
734 EXPORT_SYMBOL_GPL(dccp_v4_do_rcv);
735 
736 /**
737  *	dccp_invalid_packet  -  check for malformed packets
738  *	Implements RFC 4340, 8.5:  Step 1: Check header basics
739  *	Packets that fail these checks are ignored and do not receive Resets.
740  */
741 int dccp_invalid_packet(struct sk_buff *skb)
742 {
743 	const struct dccp_hdr *dh;
744 	unsigned int cscov;
745 
746 	if (skb->pkt_type != PACKET_HOST)
747 		return 1;
748 
749 	/* If the packet is shorter than 12 bytes, drop packet and return */
750 	if (!pskb_may_pull(skb, sizeof(struct dccp_hdr))) {
751 		DCCP_WARN("pskb_may_pull failed\n");
752 		return 1;
753 	}
754 
755 	dh = dccp_hdr(skb);
756 
757 	/* If P.type is not understood, drop packet and return */
758 	if (dh->dccph_type >= DCCP_PKT_INVALID) {
759 		DCCP_WARN("invalid packet type\n");
760 		return 1;
761 	}
762 
763 	/*
764 	 * If P.Data Offset is too small for packet type, drop packet and return
765 	 */
766 	if (dh->dccph_doff < dccp_hdr_len(skb) / sizeof(u32)) {
767 		DCCP_WARN("P.Data Offset(%u) too small\n", dh->dccph_doff);
768 		return 1;
769 	}
770 	/*
771 	 * If P.Data Offset is too too large for packet, drop packet and return
772 	 */
773 	if (!pskb_may_pull(skb, dh->dccph_doff * sizeof(u32))) {
774 		DCCP_WARN("P.Data Offset(%u) too large\n", dh->dccph_doff);
775 		return 1;
776 	}
777 
778 	/*
779 	 * If P.type is not Data, Ack, or DataAck and P.X == 0 (the packet
780 	 * has short sequence numbers), drop packet and return
781 	 */
782 	if (dh->dccph_type >= DCCP_PKT_DATA    &&
783 	    dh->dccph_type <= DCCP_PKT_DATAACK && dh->dccph_x == 0)  {
784 		DCCP_WARN("P.type (%s) not Data || [Data]Ack, while P.X == 0\n",
785 			  dccp_packet_name(dh->dccph_type));
786 		return 1;
787 	}
788 
789 	/*
790 	 * If P.CsCov is too large for the packet size, drop packet and return.
791 	 * This must come _before_ checksumming (not as RFC 4340 suggests).
792 	 */
793 	cscov = dccp_csum_coverage(skb);
794 	if (cscov > skb->len) {
795 		DCCP_WARN("P.CsCov %u exceeds packet length %d\n",
796 			  dh->dccph_cscov, skb->len);
797 		return 1;
798 	}
799 
800 	/* If header checksum is incorrect, drop packet and return.
801 	 * (This step is completed in the AF-dependent functions.) */
802 	skb->csum = skb_checksum(skb, 0, cscov, 0);
803 
804 	return 0;
805 }
806 
807 EXPORT_SYMBOL_GPL(dccp_invalid_packet);
808 
809 /* this is called when real data arrives */
810 static int dccp_v4_rcv(struct sk_buff *skb)
811 {
812 	const struct dccp_hdr *dh;
813 	const struct iphdr *iph;
814 	struct sock *sk;
815 	int min_cov;
816 
817 	/* Step 1: Check header basics */
818 
819 	if (dccp_invalid_packet(skb))
820 		goto discard_it;
821 
822 	iph = ip_hdr(skb);
823 	/* Step 1: If header checksum is incorrect, drop packet and return */
824 	if (dccp_v4_csum_finish(skb, iph->saddr, iph->daddr)) {
825 		DCCP_WARN("dropped packet with invalid checksum\n");
826 		goto discard_it;
827 	}
828 
829 	dh = dccp_hdr(skb);
830 
831 	DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(skb);
832 	DCCP_SKB_CB(skb)->dccpd_type = dh->dccph_type;
833 
834 	dccp_pr_debug("%8.8s "
835 		      "src=%u.%u.%u.%u@%-5d "
836 		      "dst=%u.%u.%u.%u@%-5d seq=%llu",
837 		      dccp_packet_name(dh->dccph_type),
838 		      NIPQUAD(iph->saddr), ntohs(dh->dccph_sport),
839 		      NIPQUAD(iph->daddr), ntohs(dh->dccph_dport),
840 		      (unsigned long long) DCCP_SKB_CB(skb)->dccpd_seq);
841 
842 	if (dccp_packet_without_ack(skb)) {
843 		DCCP_SKB_CB(skb)->dccpd_ack_seq = DCCP_PKT_WITHOUT_ACK_SEQ;
844 		dccp_pr_debug_cat("\n");
845 	} else {
846 		DCCP_SKB_CB(skb)->dccpd_ack_seq = dccp_hdr_ack_seq(skb);
847 		dccp_pr_debug_cat(", ack=%llu\n", (unsigned long long)
848 				  DCCP_SKB_CB(skb)->dccpd_ack_seq);
849 	}
850 
851 	/* Step 2:
852 	 *	Look up flow ID in table and get corresponding socket */
853 	sk = __inet_lookup(&dccp_hashinfo,
854 			   iph->saddr, dh->dccph_sport,
855 			   iph->daddr, dh->dccph_dport, inet_iif(skb));
856 	/*
857 	 * Step 2:
858 	 *	If no socket ...
859 	 */
860 	if (sk == NULL) {
861 		dccp_pr_debug("failed to look up flow ID in table and "
862 			      "get corresponding socket\n");
863 		goto no_dccp_socket;
864 	}
865 
866 	/*
867 	 * Step 2:
868 	 *	... or S.state == TIMEWAIT,
869 	 *		Generate Reset(No Connection) unless P.type == Reset
870 	 *		Drop packet and return
871 	 */
872 	if (sk->sk_state == DCCP_TIME_WAIT) {
873 		dccp_pr_debug("sk->sk_state == DCCP_TIME_WAIT: do_time_wait\n");
874 		inet_twsk_put(inet_twsk(sk));
875 		goto no_dccp_socket;
876 	}
877 
878 	/*
879 	 * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
880 	 *	o if MinCsCov = 0, only packets with CsCov = 0 are accepted
881 	 *	o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
882 	 */
883 	min_cov = dccp_sk(sk)->dccps_pcrlen;
884 	if (dh->dccph_cscov && (min_cov == 0 || dh->dccph_cscov < min_cov))  {
885 		dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
886 			      dh->dccph_cscov, min_cov);
887 		/* FIXME: "Such packets SHOULD be reported using Data Dropped
888 		 *         options (Section 11.7) with Drop Code 0, Protocol
889 		 *         Constraints."                                     */
890 		goto discard_and_relse;
891 	}
892 
893 	if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
894 		goto discard_and_relse;
895 	nf_reset(skb);
896 
897 	return sk_receive_skb(sk, skb, 1);
898 
899 no_dccp_socket:
900 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
901 		goto discard_it;
902 	/*
903 	 * Step 2:
904 	 *	If no socket ...
905 	 *		Generate Reset(No Connection) unless P.type == Reset
906 	 *		Drop packet and return
907 	 */
908 	if (dh->dccph_type != DCCP_PKT_RESET) {
909 		DCCP_SKB_CB(skb)->dccpd_reset_code =
910 					DCCP_RESET_CODE_NO_CONNECTION;
911 		dccp_v4_ctl_send_reset(sk, skb);
912 	}
913 
914 discard_it:
915 	kfree_skb(skb);
916 	return 0;
917 
918 discard_and_relse:
919 	sock_put(sk);
920 	goto discard_it;
921 }
922 
923 static struct inet_connection_sock_af_ops dccp_ipv4_af_ops = {
924 	.queue_xmit	   = ip_queue_xmit,
925 	.send_check	   = dccp_v4_send_check,
926 	.rebuild_header	   = inet_sk_rebuild_header,
927 	.conn_request	   = dccp_v4_conn_request,
928 	.syn_recv_sock	   = dccp_v4_request_recv_sock,
929 	.net_header_len	   = sizeof(struct iphdr),
930 	.setsockopt	   = ip_setsockopt,
931 	.getsockopt	   = ip_getsockopt,
932 	.addr2sockaddr	   = inet_csk_addr2sockaddr,
933 	.sockaddr_len	   = sizeof(struct sockaddr_in),
934 #ifdef CONFIG_COMPAT
935 	.compat_setsockopt = compat_ip_setsockopt,
936 	.compat_getsockopt = compat_ip_getsockopt,
937 #endif
938 };
939 
940 static int dccp_v4_init_sock(struct sock *sk)
941 {
942 	static __u8 dccp_v4_ctl_sock_initialized;
943 	int err = dccp_init_sock(sk, dccp_v4_ctl_sock_initialized);
944 
945 	if (err == 0) {
946 		if (unlikely(!dccp_v4_ctl_sock_initialized))
947 			dccp_v4_ctl_sock_initialized = 1;
948 		inet_csk(sk)->icsk_af_ops = &dccp_ipv4_af_ops;
949 	}
950 
951 	return err;
952 }
953 
954 static struct timewait_sock_ops dccp_timewait_sock_ops = {
955 	.twsk_obj_size	= sizeof(struct inet_timewait_sock),
956 };
957 
958 static struct proto dccp_v4_prot = {
959 	.name			= "DCCP",
960 	.owner			= THIS_MODULE,
961 	.close			= dccp_close,
962 	.connect		= dccp_v4_connect,
963 	.disconnect		= dccp_disconnect,
964 	.ioctl			= dccp_ioctl,
965 	.init			= dccp_v4_init_sock,
966 	.setsockopt		= dccp_setsockopt,
967 	.getsockopt		= dccp_getsockopt,
968 	.sendmsg		= dccp_sendmsg,
969 	.recvmsg		= dccp_recvmsg,
970 	.backlog_rcv		= dccp_v4_do_rcv,
971 	.hash			= dccp_hash,
972 	.unhash			= dccp_unhash,
973 	.accept			= inet_csk_accept,
974 	.get_port		= dccp_v4_get_port,
975 	.shutdown		= dccp_shutdown,
976 	.destroy		= dccp_destroy_sock,
977 	.orphan_count		= &dccp_orphan_count,
978 	.max_header		= MAX_DCCP_HEADER,
979 	.obj_size		= sizeof(struct dccp_sock),
980 	.rsk_prot		= &dccp_request_sock_ops,
981 	.twsk_prot		= &dccp_timewait_sock_ops,
982 #ifdef CONFIG_COMPAT
983 	.compat_setsockopt	= compat_dccp_setsockopt,
984 	.compat_getsockopt	= compat_dccp_getsockopt,
985 #endif
986 };
987 
988 static struct net_protocol dccp_v4_protocol = {
989 	.handler	= dccp_v4_rcv,
990 	.err_handler	= dccp_v4_err,
991 	.no_policy	= 1,
992 };
993 
994 static const struct proto_ops inet_dccp_ops = {
995 	.family		   = PF_INET,
996 	.owner		   = THIS_MODULE,
997 	.release	   = inet_release,
998 	.bind		   = inet_bind,
999 	.connect	   = inet_stream_connect,
1000 	.socketpair	   = sock_no_socketpair,
1001 	.accept		   = inet_accept,
1002 	.getname	   = inet_getname,
1003 	/* FIXME: work on tcp_poll to rename it to inet_csk_poll */
1004 	.poll		   = dccp_poll,
1005 	.ioctl		   = inet_ioctl,
1006 	/* FIXME: work on inet_listen to rename it to sock_common_listen */
1007 	.listen		   = inet_dccp_listen,
1008 	.shutdown	   = inet_shutdown,
1009 	.setsockopt	   = sock_common_setsockopt,
1010 	.getsockopt	   = sock_common_getsockopt,
1011 	.sendmsg	   = inet_sendmsg,
1012 	.recvmsg	   = sock_common_recvmsg,
1013 	.mmap		   = sock_no_mmap,
1014 	.sendpage	   = sock_no_sendpage,
1015 #ifdef CONFIG_COMPAT
1016 	.compat_setsockopt = compat_sock_common_setsockopt,
1017 	.compat_getsockopt = compat_sock_common_getsockopt,
1018 #endif
1019 };
1020 
1021 static struct inet_protosw dccp_v4_protosw = {
1022 	.type		= SOCK_DCCP,
1023 	.protocol	= IPPROTO_DCCP,
1024 	.prot		= &dccp_v4_prot,
1025 	.ops		= &inet_dccp_ops,
1026 	.capability	= -1,
1027 	.no_check	= 0,
1028 	.flags		= INET_PROTOSW_ICSK,
1029 };
1030 
1031 static int __init dccp_v4_init(void)
1032 {
1033 	int err = proto_register(&dccp_v4_prot, 1);
1034 
1035 	if (err != 0)
1036 		goto out;
1037 
1038 	err = inet_add_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
1039 	if (err != 0)
1040 		goto out_proto_unregister;
1041 
1042 	inet_register_protosw(&dccp_v4_protosw);
1043 
1044 	err = inet_csk_ctl_sock_create(&dccp_v4_ctl_socket, PF_INET,
1045 				       SOCK_DCCP, IPPROTO_DCCP);
1046 	if (err)
1047 		goto out_unregister_protosw;
1048 out:
1049 	return err;
1050 out_unregister_protosw:
1051 	inet_unregister_protosw(&dccp_v4_protosw);
1052 	inet_del_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
1053 out_proto_unregister:
1054 	proto_unregister(&dccp_v4_prot);
1055 	goto out;
1056 }
1057 
1058 static void __exit dccp_v4_exit(void)
1059 {
1060 	inet_unregister_protosw(&dccp_v4_protosw);
1061 	inet_del_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
1062 	proto_unregister(&dccp_v4_prot);
1063 }
1064 
1065 module_init(dccp_v4_init);
1066 module_exit(dccp_v4_exit);
1067 
1068 /*
1069  * __stringify doesn't likes enums, so use SOCK_DCCP (6) and IPPROTO_DCCP (33)
1070  * values directly, Also cover the case where the protocol is not specified,
1071  * i.e. net-pf-PF_INET-proto-0-type-SOCK_DCCP
1072  */
1073 MODULE_ALIAS("net-pf-" __stringify(PF_INET) "-proto-33-type-6");
1074 MODULE_ALIAS("net-pf-" __stringify(PF_INET) "-proto-0-type-6");
1075 MODULE_LICENSE("GPL");
1076 MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@mandriva.com>");
1077 MODULE_DESCRIPTION("DCCP - Datagram Congestion Controlled Protocol");
1078