1/*
2 * net/sched/ematch.c		Extended Match API
3 *
4 *		This program is free software; you can redistribute it and/or
5 *		modify it under the terms of the GNU General Public License
6 *		as published by the Free Software Foundation; either version
7 *		2 of the License, or (at your option) any later version.
8 *
9 * Authors:	Thomas Graf <tgraf@suug.ch>
10 *
11 * ==========================================================================
12 *
13 * An extended match (ematch) is a small classification tool not worth
14 * writing a full classifier for. Ematches can be interconnected to form
15 * a logic expression and get attached to classifiers to extend their
16 * functionatlity.
17 *
18 * The userspace part transforms the logic expressions into an array
19 * consisting of multiple sequences of interconnected ematches separated
20 * by markers. Precedence is implemented by a special ematch kind
21 * referencing a sequence beyond the marker of the current sequence
22 * causing the current position in the sequence to be pushed onto a stack
23 * to allow the current position to be overwritten by the position referenced
24 * in the special ematch. Matching continues in the new sequence until a
25 * marker is reached causing the position to be restored from the stack.
26 *
27 * Example:
28 *          A AND (B1 OR B2) AND C AND D
29 *
30 *              ------->-PUSH-------
31 *    -->--    /         -->--      \   -->--
32 *   /     \  /         /     \      \ /     \
33 * +-------+-------+-------+-------+-------+--------+
34 * | A AND | B AND | C AND | D END | B1 OR | B2 END |
35 * +-------+-------+-------+-------+-------+--------+
36 *                    \                      /
37 *                     --------<-POP---------
38 *
39 * where B is a virtual ematch referencing to sequence starting with B1.
40 *
41 * ==========================================================================
42 *
43 * How to write an ematch in 60 seconds
44 * ------------------------------------
45 *
46 *   1) Provide a matcher function:
47 *      static int my_match(struct sk_buff *skb, struct tcf_ematch *m,
48 *                          struct tcf_pkt_info *info)
49 *      {
50 *      	struct mydata *d = (struct mydata *) m->data;
51 *
52 *      	if (...matching goes here...)
53 *      		return 1;
54 *      	else
55 *      		return 0;
56 *      }
57 *
58 *   2) Fill out a struct tcf_ematch_ops:
59 *      static struct tcf_ematch_ops my_ops = {
60 *      	.kind = unique id,
61 *      	.datalen = sizeof(struct mydata),
62 *      	.match = my_match,
63 *      	.owner = THIS_MODULE,
64 *      };
65 *
66 *   3) Register/Unregister your ematch:
67 *      static int __init init_my_ematch(void)
68 *      {
69 *      	return tcf_em_register(&my_ops);
70 *      }
71 *
72 *      static void __exit exit_my_ematch(void)
73 *      {
74 *      	tcf_em_unregister(&my_ops);
75 *      }
76 *
77 *      module_init(init_my_ematch);
78 *      module_exit(exit_my_ematch);
79 *
80 *   4) By now you should have two more seconds left, barely enough to
81 *      open up a beer to watch the compilation going.
82 */
83
84#include <linux/module.h>
85#include <linux/slab.h>
86#include <linux/types.h>
87#include <linux/kernel.h>
88#include <linux/errno.h>
89#include <linux/rtnetlink.h>
90#include <linux/skbuff.h>
91#include <net/pkt_cls.h>
92
93static LIST_HEAD(ematch_ops);
94static DEFINE_RWLOCK(ematch_mod_lock);
95
96static struct tcf_ematch_ops *tcf_em_lookup(u16 kind)
97{
98	struct tcf_ematch_ops *e = NULL;
99
100	read_lock(&ematch_mod_lock);
101	list_for_each_entry(e, &ematch_ops, link) {
102		if (kind == e->kind) {
103			if (!try_module_get(e->owner))
104				e = NULL;
105			read_unlock(&ematch_mod_lock);
106			return e;
107		}
108	}
109	read_unlock(&ematch_mod_lock);
110
111	return NULL;
112}
113
114/**
115 * tcf_em_register - register an extended match
116 *
117 * @ops: ematch operations lookup table
118 *
119 * This function must be called by ematches to announce their presence.
120 * The given @ops must have kind set to a unique identifier and the
121 * callback match() must be implemented. All other callbacks are optional
122 * and a fallback implementation is used instead.
123 *
124 * Returns -EEXISTS if an ematch of the same kind has already registered.
125 */
126int tcf_em_register(struct tcf_ematch_ops *ops)
127{
128	int err = -EEXIST;
129	struct tcf_ematch_ops *e;
130
131	if (ops->match == NULL)
132		return -EINVAL;
133
134	write_lock(&ematch_mod_lock);
135	list_for_each_entry(e, &ematch_ops, link)
136		if (ops->kind == e->kind)
137			goto errout;
138
139	list_add_tail(&ops->link, &ematch_ops);
140	err = 0;
141errout:
142	write_unlock(&ematch_mod_lock);
143	return err;
144}
145EXPORT_SYMBOL(tcf_em_register);
146
147/**
148 * tcf_em_unregister - unregster and extended match
149 *
150 * @ops: ematch operations lookup table
151 *
152 * This function must be called by ematches to announce their disappearance
153 * for examples when the module gets unloaded. The @ops parameter must be
154 * the same as the one used for registration.
155 *
156 * Returns -ENOENT if no matching ematch was found.
157 */
158void tcf_em_unregister(struct tcf_ematch_ops *ops)
159{
160	write_lock(&ematch_mod_lock);
161	list_del(&ops->link);
162	write_unlock(&ematch_mod_lock);
163}
164EXPORT_SYMBOL(tcf_em_unregister);
165
166static inline struct tcf_ematch *tcf_em_get_match(struct tcf_ematch_tree *tree,
167						  int index)
168{
169	return &tree->matches[index];
170}
171
172
173static int tcf_em_validate(struct tcf_proto *tp,
174			   struct tcf_ematch_tree_hdr *tree_hdr,
175			   struct tcf_ematch *em, struct nlattr *nla, int idx)
176{
177	int err = -EINVAL;
178	struct tcf_ematch_hdr *em_hdr = nla_data(nla);
179	int data_len = nla_len(nla) - sizeof(*em_hdr);
180	void *data = (void *) em_hdr + sizeof(*em_hdr);
181	struct net *net = dev_net(qdisc_dev(tp->q));
182
183	if (!TCF_EM_REL_VALID(em_hdr->flags))
184		goto errout;
185
186	if (em_hdr->kind == TCF_EM_CONTAINER) {
187		/* Special ematch called "container", carries an index
188		 * referencing an external ematch sequence.
189		 */
190		u32 ref;
191
192		if (data_len < sizeof(ref))
193			goto errout;
194		ref = *(u32 *) data;
195
196		if (ref >= tree_hdr->nmatches)
197			goto errout;
198
199		/* We do not allow backward jumps to avoid loops and jumps
200		 * to our own position are of course illegal.
201		 */
202		if (ref <= idx)
203			goto errout;
204
205
206		em->data = ref;
207	} else {
208		/* Note: This lookup will increase the module refcnt
209		 * of the ematch module referenced. In case of a failure,
210		 * a destroy function is called by the underlying layer
211		 * which automatically releases the reference again, therefore
212		 * the module MUST not be given back under any circumstances
213		 * here. Be aware, the destroy function assumes that the
214		 * module is held if the ops field is non zero.
215		 */
216		em->ops = tcf_em_lookup(em_hdr->kind);
217
218		if (em->ops == NULL) {
219			err = -ENOENT;
220#ifdef CONFIG_MODULES
221			__rtnl_unlock();
222			request_module("ematch-kind-%u", em_hdr->kind);
223			rtnl_lock();
224			em->ops = tcf_em_lookup(em_hdr->kind);
225			if (em->ops) {
226				/* We dropped the RTNL mutex in order to
227				 * perform the module load. Tell the caller
228				 * to replay the request.
229				 */
230				module_put(em->ops->owner);
231				err = -EAGAIN;
232			}
233#endif
234			goto errout;
235		}
236
237		/* ematch module provides expected length of data, so we
238		 * can do a basic sanity check.
239		 */
240		if (em->ops->datalen && data_len < em->ops->datalen)
241			goto errout;
242
243		if (em->ops->change) {
244			err = em->ops->change(net, data, data_len, em);
245			if (err < 0)
246				goto errout;
247		} else if (data_len > 0) {
248			/* ematch module doesn't provide an own change
249			 * procedure and expects us to allocate and copy
250			 * the ematch data.
251			 *
252			 * TCF_EM_SIMPLE may be specified stating that the
253			 * data only consists of a u32 integer and the module
254			 * does not expected a memory reference but rather
255			 * the value carried.
256			 */
257			if (em_hdr->flags & TCF_EM_SIMPLE) {
258				if (data_len < sizeof(u32))
259					goto errout;
260				em->data = *(u32 *) data;
261			} else {
262				void *v = kmemdup(data, data_len, GFP_KERNEL);
263				if (v == NULL) {
264					err = -ENOBUFS;
265					goto errout;
266				}
267				em->data = (unsigned long) v;
268			}
269		}
270	}
271
272	em->matchid = em_hdr->matchid;
273	em->flags = em_hdr->flags;
274	em->datalen = data_len;
275	em->net = net;
276
277	err = 0;
278errout:
279	return err;
280}
281
282static const struct nla_policy em_policy[TCA_EMATCH_TREE_MAX + 1] = {
283	[TCA_EMATCH_TREE_HDR]	= { .len = sizeof(struct tcf_ematch_tree_hdr) },
284	[TCA_EMATCH_TREE_LIST]	= { .type = NLA_NESTED },
285};
286
287/**
288 * tcf_em_tree_validate - validate ematch config TLV and build ematch tree
289 *
290 * @tp: classifier kind handle
291 * @nla: ematch tree configuration TLV
292 * @tree: destination ematch tree variable to store the resulting
293 *        ematch tree.
294 *
295 * This function validates the given configuration TLV @nla and builds an
296 * ematch tree in @tree. The resulting tree must later be copied into
297 * the private classifier data using tcf_em_tree_change(). You MUST NOT
298 * provide the ematch tree variable of the private classifier data directly,
299 * the changes would not be locked properly.
300 *
301 * Returns a negative error code if the configuration TLV contains errors.
302 */
303int tcf_em_tree_validate(struct tcf_proto *tp, struct nlattr *nla,
304			 struct tcf_ematch_tree *tree)
305{
306	int idx, list_len, matches_len, err;
307	struct nlattr *tb[TCA_EMATCH_TREE_MAX + 1];
308	struct nlattr *rt_match, *rt_hdr, *rt_list;
309	struct tcf_ematch_tree_hdr *tree_hdr;
310	struct tcf_ematch *em;
311
312	memset(tree, 0, sizeof(*tree));
313	if (!nla)
314		return 0;
315
316	err = nla_parse_nested(tb, TCA_EMATCH_TREE_MAX, nla, em_policy);
317	if (err < 0)
318		goto errout;
319
320	err = -EINVAL;
321	rt_hdr = tb[TCA_EMATCH_TREE_HDR];
322	rt_list = tb[TCA_EMATCH_TREE_LIST];
323
324	if (rt_hdr == NULL || rt_list == NULL)
325		goto errout;
326
327	tree_hdr = nla_data(rt_hdr);
328	memcpy(&tree->hdr, tree_hdr, sizeof(*tree_hdr));
329
330	rt_match = nla_data(rt_list);
331	list_len = nla_len(rt_list);
332	matches_len = tree_hdr->nmatches * sizeof(*em);
333
334	tree->matches = kzalloc(matches_len, GFP_KERNEL);
335	if (tree->matches == NULL)
336		goto errout;
337
338	/* We do not use nla_parse_nested here because the maximum
339	 * number of attributes is unknown. This saves us the allocation
340	 * for a tb buffer which would serve no purpose at all.
341	 *
342	 * The array of rt attributes is parsed in the order as they are
343	 * provided, their type must be incremental from 1 to n. Even
344	 * if it does not serve any real purpose, a failure of sticking
345	 * to this policy will result in parsing failure.
346	 */
347	for (idx = 0; nla_ok(rt_match, list_len); idx++) {
348		err = -EINVAL;
349
350		if (rt_match->nla_type != (idx + 1))
351			goto errout_abort;
352
353		if (idx >= tree_hdr->nmatches)
354			goto errout_abort;
355
356		if (nla_len(rt_match) < sizeof(struct tcf_ematch_hdr))
357			goto errout_abort;
358
359		em = tcf_em_get_match(tree, idx);
360
361		err = tcf_em_validate(tp, tree_hdr, em, rt_match, idx);
362		if (err < 0)
363			goto errout_abort;
364
365		rt_match = nla_next(rt_match, &list_len);
366	}
367
368	/* Check if the number of matches provided by userspace actually
369	 * complies with the array of matches. The number was used for
370	 * the validation of references and a mismatch could lead to
371	 * undefined references during the matching process.
372	 */
373	if (idx != tree_hdr->nmatches) {
374		err = -EINVAL;
375		goto errout_abort;
376	}
377
378	err = 0;
379errout:
380	return err;
381
382errout_abort:
383	tcf_em_tree_destroy(tree);
384	return err;
385}
386EXPORT_SYMBOL(tcf_em_tree_validate);
387
388/**
389 * tcf_em_tree_destroy - destroy an ematch tree
390 *
391 * @tp: classifier kind handle
392 * @tree: ematch tree to be deleted
393 *
394 * This functions destroys an ematch tree previously created by
395 * tcf_em_tree_validate()/tcf_em_tree_change(). You must ensure that
396 * the ematch tree is not in use before calling this function.
397 */
398void tcf_em_tree_destroy(struct tcf_ematch_tree *tree)
399{
400	int i;
401
402	if (tree->matches == NULL)
403		return;
404
405	for (i = 0; i < tree->hdr.nmatches; i++) {
406		struct tcf_ematch *em = tcf_em_get_match(tree, i);
407
408		if (em->ops) {
409			if (em->ops->destroy)
410				em->ops->destroy(em);
411			else if (!tcf_em_is_simple(em))
412				kfree((void *) em->data);
413			module_put(em->ops->owner);
414		}
415	}
416
417	tree->hdr.nmatches = 0;
418	kfree(tree->matches);
419	tree->matches = NULL;
420}
421EXPORT_SYMBOL(tcf_em_tree_destroy);
422
423/**
424 * tcf_em_tree_dump - dump ematch tree into a rtnl message
425 *
426 * @skb: skb holding the rtnl message
427 * @t: ematch tree to be dumped
428 * @tlv: TLV type to be used to encapsulate the tree
429 *
430 * This function dumps a ematch tree into a rtnl message. It is valid to
431 * call this function while the ematch tree is in use.
432 *
433 * Returns -1 if the skb tailroom is insufficient.
434 */
435int tcf_em_tree_dump(struct sk_buff *skb, struct tcf_ematch_tree *tree, int tlv)
436{
437	int i;
438	u8 *tail;
439	struct nlattr *top_start;
440	struct nlattr *list_start;
441
442	top_start = nla_nest_start(skb, tlv);
443	if (top_start == NULL)
444		goto nla_put_failure;
445
446	if (nla_put(skb, TCA_EMATCH_TREE_HDR, sizeof(tree->hdr), &tree->hdr))
447		goto nla_put_failure;
448
449	list_start = nla_nest_start(skb, TCA_EMATCH_TREE_LIST);
450	if (list_start == NULL)
451		goto nla_put_failure;
452
453	tail = skb_tail_pointer(skb);
454	for (i = 0; i < tree->hdr.nmatches; i++) {
455		struct nlattr *match_start = (struct nlattr *)tail;
456		struct tcf_ematch *em = tcf_em_get_match(tree, i);
457		struct tcf_ematch_hdr em_hdr = {
458			.kind = em->ops ? em->ops->kind : TCF_EM_CONTAINER,
459			.matchid = em->matchid,
460			.flags = em->flags
461		};
462
463		if (nla_put(skb, i + 1, sizeof(em_hdr), &em_hdr))
464			goto nla_put_failure;
465
466		if (em->ops && em->ops->dump) {
467			if (em->ops->dump(skb, em) < 0)
468				goto nla_put_failure;
469		} else if (tcf_em_is_container(em) || tcf_em_is_simple(em)) {
470			u32 u = em->data;
471			nla_put_nohdr(skb, sizeof(u), &u);
472		} else if (em->datalen > 0)
473			nla_put_nohdr(skb, em->datalen, (void *) em->data);
474
475		tail = skb_tail_pointer(skb);
476		match_start->nla_len = tail - (u8 *)match_start;
477	}
478
479	nla_nest_end(skb, list_start);
480	nla_nest_end(skb, top_start);
481
482	return 0;
483
484nla_put_failure:
485	return -1;
486}
487EXPORT_SYMBOL(tcf_em_tree_dump);
488
489static inline int tcf_em_match(struct sk_buff *skb, struct tcf_ematch *em,
490			       struct tcf_pkt_info *info)
491{
492	int r = em->ops->match(skb, em, info);
493
494	return tcf_em_is_inverted(em) ? !r : r;
495}
496
497/* Do not use this function directly, use tcf_em_tree_match instead */
498int __tcf_em_tree_match(struct sk_buff *skb, struct tcf_ematch_tree *tree,
499			struct tcf_pkt_info *info)
500{
501	int stackp = 0, match_idx = 0, res = 0;
502	struct tcf_ematch *cur_match;
503	int stack[CONFIG_NET_EMATCH_STACK];
504
505proceed:
506	while (match_idx < tree->hdr.nmatches) {
507		cur_match = tcf_em_get_match(tree, match_idx);
508
509		if (tcf_em_is_container(cur_match)) {
510			if (unlikely(stackp >= CONFIG_NET_EMATCH_STACK))
511				goto stack_overflow;
512
513			stack[stackp++] = match_idx;
514			match_idx = cur_match->data;
515			goto proceed;
516		}
517
518		res = tcf_em_match(skb, cur_match, info);
519
520		if (tcf_em_early_end(cur_match, res))
521			break;
522
523		match_idx++;
524	}
525
526pop_stack:
527	if (stackp > 0) {
528		match_idx = stack[--stackp];
529		cur_match = tcf_em_get_match(tree, match_idx);
530
531		if (tcf_em_is_inverted(cur_match))
532			res = !res;
533
534		if (tcf_em_early_end(cur_match, res)) {
535			goto pop_stack;
536		} else {
537			match_idx++;
538			goto proceed;
539		}
540	}
541
542	return res;
543
544stack_overflow:
545	net_warn_ratelimited("tc ematch: local stack overflow, increase NET_EMATCH_STACK\n");
546	return -1;
547}
548EXPORT_SYMBOL(__tcf_em_tree_match);
549