1/*-
2 * ng_tcpmss.c
3 *
4 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
5 *
6 * Copyright (c) 2004, Alexey Popov <lollypop@flexuser.ru>
7 * All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 *    notice unmodified, this list of conditions, and the following
14 *    disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 *
31 * This software includes fragments of the following programs:
32 *	tcpmssd		Ruslan Ermilov <ru@FreeBSD.org>
33 *
34 * $FreeBSD$
35 */
36
37/*
38 * This node is netgraph tool for workaround of PMTUD problem. It acts
39 * like filter for IP packets. If configured, it reduces MSS of TCP SYN
40 * packets.
41 *
42 * Configuration can be done by sending NGM_TCPMSS_CONFIG message. The
43 * message sets filter for incoming packets on hook 'inHook'. Packet's
44 * TCP MSS field is lowered to 'maxMSS' parameter and resulting packet
45 * is sent to 'outHook'.
46 *
47 * XXX: statistics are updated not atomically, so they may broke on SMP.
48 */
49
50#include <sys/param.h>
51#include <sys/systm.h>
52#include <sys/endian.h>
53#include <sys/errno.h>
54#include <sys/kernel.h>
55#include <sys/malloc.h>
56#include <sys/mbuf.h>
57
58#include <netinet/in.h>
59#include <netinet/in_systm.h>
60#include <netinet/ip.h>
61#include <netinet/tcp.h>
62
63#include <netgraph/ng_message.h>
64#include <netgraph/netgraph.h>
65#include <netgraph/ng_parse.h>
66#include <netgraph/ng_tcpmss.h>
67
68/* Per hook info. */
69typedef struct {
70	hook_p				outHook;
71	struct ng_tcpmss_hookstat	stats;
72} *hpriv_p;
73
74/* Netgraph methods. */
75static ng_constructor_t	ng_tcpmss_constructor;
76static ng_rcvmsg_t	ng_tcpmss_rcvmsg;
77static ng_newhook_t	ng_tcpmss_newhook;
78static ng_rcvdata_t	ng_tcpmss_rcvdata;
79static ng_disconnect_t	ng_tcpmss_disconnect;
80
81static int correct_mss(struct tcphdr *, int, uint16_t, int);
82
83/* Parse type for struct ng_tcpmss_hookstat. */
84static const struct ng_parse_struct_field ng_tcpmss_hookstat_type_fields[]
85	= NG_TCPMSS_HOOKSTAT_INFO;
86static const struct ng_parse_type ng_tcpmss_hookstat_type = {
87	&ng_parse_struct_type,
88	&ng_tcpmss_hookstat_type_fields
89};
90
91/* Parse type for struct ng_tcpmss_config. */
92static const struct ng_parse_struct_field ng_tcpmss_config_type_fields[]
93	= NG_TCPMSS_CONFIG_INFO;
94static const struct ng_parse_type ng_tcpmss_config_type = {
95	&ng_parse_struct_type,
96	ng_tcpmss_config_type_fields
97};
98
99/* List of commands and how to convert arguments to/from ASCII. */
100static const struct ng_cmdlist ng_tcpmss_cmds[] = {
101	{
102	  NGM_TCPMSS_COOKIE,
103	  NGM_TCPMSS_GET_STATS,
104	  "getstats",
105	  &ng_parse_hookbuf_type,
106	  &ng_tcpmss_hookstat_type
107	},
108	{
109	  NGM_TCPMSS_COOKIE,
110	  NGM_TCPMSS_CLR_STATS,
111	  "clrstats",
112	  &ng_parse_hookbuf_type,
113	  NULL
114	},
115	{
116	  NGM_TCPMSS_COOKIE,
117	  NGM_TCPMSS_GETCLR_STATS,
118	  "getclrstats",
119	  &ng_parse_hookbuf_type,
120	  &ng_tcpmss_hookstat_type
121	},
122	{
123	  NGM_TCPMSS_COOKIE,
124	  NGM_TCPMSS_CONFIG,
125	  "config",
126	  &ng_tcpmss_config_type,
127	  NULL
128	},
129	{ 0 }
130};
131
132/* Netgraph type descriptor. */
133static struct ng_type ng_tcpmss_typestruct = {
134	.version =	NG_ABI_VERSION,
135	.name =		NG_TCPMSS_NODE_TYPE,
136	.constructor =	ng_tcpmss_constructor,
137	.rcvmsg =	ng_tcpmss_rcvmsg,
138	.newhook =	ng_tcpmss_newhook,
139	.rcvdata =	ng_tcpmss_rcvdata,
140	.disconnect =	ng_tcpmss_disconnect,
141	.cmdlist =	ng_tcpmss_cmds,
142};
143
144NETGRAPH_INIT(tcpmss, &ng_tcpmss_typestruct);
145
146#define	ERROUT(x)	{ error = (x); goto done; }
147
148/*
149 * Node constructor. No special actions required.
150 */
151static int
152ng_tcpmss_constructor(node_p node)
153{
154	return (0);
155}
156
157/*
158 * Add a hook. Any unique name is OK.
159 */
160static int
161ng_tcpmss_newhook(node_p node, hook_p hook, const char *name)
162{
163	hpriv_p priv;
164
165	priv = malloc(sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
166	if (priv == NULL)
167		return (ENOMEM);
168
169	NG_HOOK_SET_PRIVATE(hook, priv);
170
171	return (0);
172}
173
174/*
175 * Receive a control message.
176 */
177static int
178ng_tcpmss_rcvmsg
179(node_p node, item_p item, hook_p lasthook)
180{
181	struct ng_mesg *msg, *resp = NULL;
182	int error = 0;
183
184	NGI_GET_MSG(item, msg);
185
186	switch (msg->header.typecookie) {
187	case NGM_TCPMSS_COOKIE:
188		switch (msg->header.cmd) {
189		case NGM_TCPMSS_GET_STATS:
190		case NGM_TCPMSS_CLR_STATS:
191		case NGM_TCPMSS_GETCLR_STATS:
192		    {
193			hook_p hook;
194			hpriv_p priv;
195
196			/* Check that message is long enough. */
197			if (msg->header.arglen != NG_HOOKSIZ)
198				ERROUT(EINVAL);
199
200			/* Find this hook. */
201			hook = ng_findhook(node, (char *)msg->data);
202			if (hook == NULL)
203				ERROUT(ENOENT);
204
205			priv = NG_HOOK_PRIVATE(hook);
206
207			/* Create response. */
208			if (msg->header.cmd != NGM_TCPMSS_CLR_STATS) {
209				NG_MKRESPONSE(resp, msg,
210				    sizeof(struct ng_tcpmss_hookstat), M_NOWAIT);
211				if (resp == NULL)
212					ERROUT(ENOMEM);
213				bcopy(&priv->stats, resp->data,
214				    sizeof(struct ng_tcpmss_hookstat));
215			}
216
217			if (msg->header.cmd != NGM_TCPMSS_GET_STATS)
218				bzero(&priv->stats,
219				    sizeof(struct ng_tcpmss_hookstat));
220			break;
221		    }
222		case NGM_TCPMSS_CONFIG:
223		    {
224			struct ng_tcpmss_config *set;
225			hook_p in, out;
226			hpriv_p priv;
227
228			/* Check that message is long enough. */
229			if (msg->header.arglen !=
230			    sizeof(struct ng_tcpmss_config))
231				ERROUT(EINVAL);
232
233			set = (struct ng_tcpmss_config *)msg->data;
234			in = ng_findhook(node, set->inHook);
235			out = ng_findhook(node, set->outHook);
236			if (in == NULL || out == NULL)
237				ERROUT(ENOENT);
238
239			/* Configure MSS hack. */
240			priv = NG_HOOK_PRIVATE(in);
241			priv->outHook = out;
242			priv->stats.maxMSS = set->maxMSS;
243
244			break;
245 		    }
246		default:
247			error = EINVAL;
248			break;
249		}
250		break;
251	default:
252		error = EINVAL;
253		break;
254	}
255
256done:
257	NG_RESPOND_MSG(error, node, item, resp);
258	NG_FREE_MSG(msg);
259
260	return (error);
261}
262
263/*
264 * Receive data on a hook, and hack MSS.
265 *
266 */
267static int
268ng_tcpmss_rcvdata(hook_p hook, item_p item)
269{
270	hpriv_p priv = NG_HOOK_PRIVATE(hook);
271	struct mbuf *m = NULL;
272	struct ip *ip;
273	struct tcphdr *tcp;
274	int iphlen, tcphlen, pktlen;
275	int pullup_len = 0;
276	int error = 0;
277
278	/* Drop packets if filter is not configured on this hook. */
279	if (priv->outHook == NULL)
280		goto done;
281
282	NGI_GET_M(item, m);
283
284	/* Update stats on incoming hook. */
285	pktlen = m->m_pkthdr.len;
286	priv->stats.Octets += pktlen;
287	priv->stats.Packets++;
288
289	/* Check whether we configured to fix MSS. */
290	if (priv->stats.maxMSS == 0)
291		goto send;
292
293#define	M_CHECK(length) do {					\
294	pullup_len += length;					\
295	if ((m)->m_pkthdr.len < pullup_len)			\
296		goto send;					\
297	if ((m)->m_len < pullup_len &&				\
298	   (((m) = m_pullup((m), pullup_len)) == NULL))		\
299		ERROUT(ENOBUFS);				\
300	} while (0)
301
302	/* Check mbuf packet size and arrange for IP header. */
303	M_CHECK(sizeof(struct ip));
304	ip = mtod(m, struct ip *);
305
306	/* Check IP version. */
307	if (ip->ip_v != IPVERSION)
308		ERROUT(EINVAL);
309
310	/* Check IP header length. */
311	iphlen = ip->ip_hl << 2;
312	if (iphlen < sizeof(struct ip) || iphlen > pktlen )
313		ERROUT(EINVAL);
314
315        /* Check if it is TCP. */
316	if (!(ip->ip_p == IPPROTO_TCP))
317		goto send;
318
319	/* Check mbuf packet size and arrange for IP+TCP header */
320	M_CHECK(iphlen - sizeof(struct ip) + sizeof(struct tcphdr));
321	ip = mtod(m, struct ip *);
322	tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
323
324	/* Check TCP header length. */
325	tcphlen = tcp->th_off << 2;
326	if (tcphlen < sizeof(struct tcphdr) || tcphlen > pktlen - iphlen)
327		ERROUT(EINVAL);
328
329	/* Check SYN packet and has options. */
330	if (!(tcp->th_flags & TH_SYN) || tcphlen == sizeof(struct tcphdr))
331		goto send;
332
333	/* Update SYN stats. */
334	priv->stats.SYNPkts++;
335
336	M_CHECK(tcphlen - sizeof(struct tcphdr));
337	ip = mtod(m, struct ip *);
338	tcp = (struct tcphdr *)((caddr_t )ip + iphlen);
339
340#undef	M_CHECK
341
342	/* Fix MSS and update stats. */
343	if (correct_mss(tcp, tcphlen, priv->stats.maxMSS,
344	    m->m_pkthdr.csum_flags))
345		priv->stats.FixedPkts++;
346
347send:
348	/* Deliver frame out destination hook. */
349	NG_FWD_NEW_DATA(error, item, priv->outHook, m);
350
351	return (error);
352
353done:
354	NG_FREE_ITEM(item);
355	NG_FREE_M(m);
356
357	return (error);
358}
359
360/*
361 * Hook disconnection.
362 * We must check all hooks, since they may reference this one.
363 */
364static int
365ng_tcpmss_disconnect(hook_p hook)
366{
367	node_p node = NG_HOOK_NODE(hook);
368	hook_p hook2;
369
370	LIST_FOREACH(hook2, &node->nd_hooks, hk_hooks) {
371		hpriv_p priv = NG_HOOK_PRIVATE(hook2);
372
373		if (priv->outHook == hook)
374			priv->outHook = NULL;
375	}
376
377	free(NG_HOOK_PRIVATE(hook), M_NETGRAPH);
378
379	if (NG_NODE_NUMHOOKS(NG_HOOK_NODE(hook)) == 0)
380		ng_rmnode_self(NG_HOOK_NODE(hook));
381
382	return (0);
383}
384
385/*
386 * Code from tcpmssd.
387 */
388
389/*-
390 * The following macro is used to update an
391 * internet checksum.  "acc" is a 32-bit
392 * accumulation of all the changes to the
393 * checksum (adding in old 16-bit words and
394 * subtracting out new words), and "cksum"
395 * is the checksum value to be updated.
396 */
397#define TCPMSS_ADJUST_CHECKSUM(acc, cksum) do {		\
398	acc += cksum;					\
399	if (acc < 0) {					\
400		acc = -acc;				\
401		acc = (acc >> 16) + (acc & 0xffff);	\
402		acc += acc >> 16;			\
403		cksum = (u_short) ~acc;			\
404	} else {					\
405		acc = (acc >> 16) + (acc & 0xffff);	\
406		acc += acc >> 16;			\
407		cksum = (u_short) acc;			\
408	}						\
409} while (0);
410
411static int
412correct_mss(struct tcphdr *tc, int hlen, uint16_t maxmss, int flags)
413{
414	int olen, optlen;
415	u_char *opt;
416	int accumulate;
417	int res = 0;
418	uint16_t sum;
419
420	for (olen = hlen - sizeof(struct tcphdr), opt = (u_char *)(tc + 1);
421	     olen > 0; olen -= optlen, opt += optlen) {
422		if (*opt == TCPOPT_EOL)
423			break;
424		else if (*opt == TCPOPT_NOP)
425			optlen = 1;
426		else {
427			optlen = *(opt + 1);
428			if (optlen <= 0 || optlen > olen)
429				break;
430			if (*opt == TCPOPT_MAXSEG) {
431				if (optlen != TCPOLEN_MAXSEG)
432					continue;
433				accumulate = be16dec(opt + 2);
434				if (accumulate > maxmss) {
435					if ((flags & CSUM_TCP) == 0) {
436						accumulate -= maxmss;
437						sum = be16dec(&tc->th_sum);
438						TCPMSS_ADJUST_CHECKSUM(accumulate, sum);
439						be16enc(&tc->th_sum, sum);
440					}
441					be16enc(opt + 2, maxmss);
442					res = 1;
443				}
444			}
445		}
446	}
447	return (res);
448}
449