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 *      	return 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/types.h>
86#include <linux/kernel.h>
87#include <linux/mm.h>
88#include <linux/errno.h>
89#include <linux/interrupt.h>
90#include <linux/rtnetlink.h>
91#include <linux/skbuff.h>
92#include <net/pkt_cls.h>
93
94static LIST_HEAD(ematch_ops);
95static DEFINE_RWLOCK(ematch_mod_lock);
96
97static inline struct tcf_ematch_ops * tcf_em_lookup(u16 kind)
98{
99	struct tcf_ematch_ops *e = NULL;
100
101	read_lock(&ematch_mod_lock);
102	list_for_each_entry(e, &ematch_ops, link) {
103		if (kind == e->kind) {
104			if (!try_module_get(e->owner))
105				e = NULL;
106			read_unlock(&ematch_mod_lock);
107			return e;
108		}
109	}
110	read_unlock(&ematch_mod_lock);
111
112	return NULL;
113}
114
115/**
116 * tcf_em_register - register an extended match
117 *
118 * @ops: ematch operations lookup table
119 *
120 * This function must be called by ematches to announce their presence.
121 * The given @ops must have kind set to a unique identifier and the
122 * callback match() must be implemented. All other callbacks are optional
123 * and a fallback implementation is used instead.
124 *
125 * Returns -EEXISTS if an ematch of the same kind has already registered.
126 */
127int tcf_em_register(struct tcf_ematch_ops *ops)
128{
129	int err = -EEXIST;
130	struct tcf_ematch_ops *e;
131
132	if (ops->match == NULL)
133		return -EINVAL;
134
135	write_lock(&ematch_mod_lock);
136	list_for_each_entry(e, &ematch_ops, link)
137		if (ops->kind == e->kind)
138			goto errout;
139
140	list_add_tail(&ops->link, &ematch_ops);
141	err = 0;
142errout:
143	write_unlock(&ematch_mod_lock);
144	return err;
145}
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 */
158int tcf_em_unregister(struct tcf_ematch_ops *ops)
159{
160	int err = 0;
161	struct tcf_ematch_ops *e;
162
163	write_lock(&ematch_mod_lock);
164	list_for_each_entry(e, &ematch_ops, link) {
165		if (e == ops) {
166			list_del(&e->link);
167			goto out;
168		}
169	}
170
171	err = -ENOENT;
172out:
173	write_unlock(&ematch_mod_lock);
174	return err;
175}
176
177static inline struct tcf_ematch * tcf_em_get_match(struct tcf_ematch_tree *tree,
178						   int index)
179{
180	return &tree->matches[index];
181}
182
183
184static int tcf_em_validate(struct tcf_proto *tp,
185			   struct tcf_ematch_tree_hdr *tree_hdr,
186			   struct tcf_ematch *em, struct rtattr *rta, int idx)
187{
188	int err = -EINVAL;
189	struct tcf_ematch_hdr *em_hdr = RTA_DATA(rta);
190	int data_len = RTA_PAYLOAD(rta) - sizeof(*em_hdr);
191	void *data = (void *) em_hdr + sizeof(*em_hdr);
192
193	if (!TCF_EM_REL_VALID(em_hdr->flags))
194		goto errout;
195
196	if (em_hdr->kind == TCF_EM_CONTAINER) {
197		/* Special ematch called "container", carries an index
198		 * referencing an external ematch sequence. */
199		u32 ref;
200
201		if (data_len < sizeof(ref))
202			goto errout;
203		ref = *(u32 *) data;
204
205		if (ref >= tree_hdr->nmatches)
206			goto errout;
207
208		/* We do not allow backward jumps to avoid loops and jumps
209		 * to our own position are of course illegal. */
210		if (ref <= idx)
211			goto errout;
212
213
214		em->data = ref;
215	} else {
216		/* Note: This lookup will increase the module refcnt
217		 * of the ematch module referenced. In case of a failure,
218		 * a destroy function is called by the underlying layer
219		 * which automatically releases the reference again, therefore
220		 * the module MUST not be given back under any circumstances
221		 * here. Be aware, the destroy function assumes that the
222		 * module is held if the ops field is non zero. */
223		em->ops = tcf_em_lookup(em_hdr->kind);
224
225		if (em->ops == NULL) {
226			err = -ENOENT;
227			goto errout;
228		}
229
230		/* ematch module provides expected length of data, so we
231		 * can do a basic sanity check. */
232		if (em->ops->datalen && data_len < em->ops->datalen)
233			goto errout;
234
235		if (em->ops->change) {
236			err = em->ops->change(tp, data, data_len, em);
237			if (err < 0)
238				goto errout;
239		} else if (data_len > 0) {
240			/* ematch module doesn't provide an own change
241			 * procedure and expects us to allocate and copy
242			 * the ematch data.
243			 *
244			 * TCF_EM_SIMPLE may be specified stating that the
245			 * data only consists of a u32 integer and the module
246			 * does not expected a memory reference but rather
247			 * the value carried. */
248			if (em_hdr->flags & TCF_EM_SIMPLE) {
249				if (data_len < sizeof(u32))
250					goto errout;
251				em->data = *(u32 *) data;
252			} else {
253				void *v = kmemdup(data, data_len, GFP_KERNEL);
254				if (v == NULL) {
255					err = -ENOBUFS;
256					goto errout;
257				}
258				em->data = (unsigned long) v;
259			}
260		}
261	}
262
263	em->matchid = em_hdr->matchid;
264	em->flags = em_hdr->flags;
265	em->datalen = data_len;
266
267	err = 0;
268errout:
269	return err;
270}
271
272/**
273 * tcf_em_tree_validate - validate ematch config TLV and build ematch tree
274 *
275 * @tp: classifier kind handle
276 * @rta: ematch tree configuration TLV
277 * @tree: destination ematch tree variable to store the resulting
278 *        ematch tree.
279 *
280 * This function validates the given configuration TLV @rta and builds an
281 * ematch tree in @tree. The resulting tree must later be copied into
282 * the private classifier data using tcf_em_tree_change(). You MUST NOT
283 * provide the ematch tree variable of the private classifier data directly,
284 * the changes would not be locked properly.
285 *
286 * Returns a negative error code if the configuration TLV contains errors.
287 */
288int tcf_em_tree_validate(struct tcf_proto *tp, struct rtattr *rta,
289			 struct tcf_ematch_tree *tree)
290{
291	int idx, list_len, matches_len, err = -EINVAL;
292	struct rtattr *tb[TCA_EMATCH_TREE_MAX];
293	struct rtattr *rt_match, *rt_hdr, *rt_list;
294	struct tcf_ematch_tree_hdr *tree_hdr;
295	struct tcf_ematch *em;
296
297	if (!rta) {
298		memset(tree, 0, sizeof(*tree));
299		return 0;
300	}
301
302	if (rtattr_parse_nested(tb, TCA_EMATCH_TREE_MAX, rta) < 0)
303		goto errout;
304
305	rt_hdr = tb[TCA_EMATCH_TREE_HDR-1];
306	rt_list = tb[TCA_EMATCH_TREE_LIST-1];
307
308	if (rt_hdr == NULL || rt_list == NULL)
309		goto errout;
310
311	if (RTA_PAYLOAD(rt_hdr) < sizeof(*tree_hdr) ||
312	    RTA_PAYLOAD(rt_list) < sizeof(*rt_match))
313		goto errout;
314
315	tree_hdr = RTA_DATA(rt_hdr);
316	memcpy(&tree->hdr, tree_hdr, sizeof(*tree_hdr));
317
318	rt_match = RTA_DATA(rt_list);
319	list_len = RTA_PAYLOAD(rt_list);
320	matches_len = tree_hdr->nmatches * sizeof(*em);
321
322	tree->matches = kzalloc(matches_len, GFP_KERNEL);
323	if (tree->matches == NULL)
324		goto errout;
325
326	/* We do not use rtattr_parse_nested here because the maximum
327	 * number of attributes is unknown. This saves us the allocation
328	 * for a tb buffer which would serve no purpose at all.
329	 *
330	 * The array of rt attributes is parsed in the order as they are
331	 * provided, their type must be incremental from 1 to n. Even
332	 * if it does not serve any real purpose, a failure of sticking
333	 * to this policy will result in parsing failure. */
334	for (idx = 0; RTA_OK(rt_match, list_len); idx++) {
335		err = -EINVAL;
336
337		if (rt_match->rta_type != (idx + 1))
338			goto errout_abort;
339
340		if (idx >= tree_hdr->nmatches)
341			goto errout_abort;
342
343		if (RTA_PAYLOAD(rt_match) < sizeof(struct tcf_ematch_hdr))
344			goto errout_abort;
345
346		em = tcf_em_get_match(tree, idx);
347
348		err = tcf_em_validate(tp, tree_hdr, em, rt_match, idx);
349		if (err < 0)
350			goto errout_abort;
351
352		rt_match = RTA_NEXT(rt_match, list_len);
353	}
354
355	/* Check if the number of matches provided by userspace actually
356	 * complies with the array of matches. The number was used for
357	 * the validation of references and a mismatch could lead to
358	 * undefined references during the matching process. */
359	if (idx != tree_hdr->nmatches) {
360		err = -EINVAL;
361		goto errout_abort;
362	}
363
364	err = 0;
365errout:
366	return err;
367
368errout_abort:
369	tcf_em_tree_destroy(tp, tree);
370	return err;
371}
372
373/**
374 * tcf_em_tree_destroy - destroy an ematch tree
375 *
376 * @tp: classifier kind handle
377 * @tree: ematch tree to be deleted
378 *
379 * This functions destroys an ematch tree previously created by
380 * tcf_em_tree_validate()/tcf_em_tree_change(). You must ensure that
381 * the ematch tree is not in use before calling this function.
382 */
383void tcf_em_tree_destroy(struct tcf_proto *tp, struct tcf_ematch_tree *tree)
384{
385	int i;
386
387	if (tree->matches == NULL)
388		return;
389
390	for (i = 0; i < tree->hdr.nmatches; i++) {
391		struct tcf_ematch *em = tcf_em_get_match(tree, i);
392
393		if (em->ops) {
394			if (em->ops->destroy)
395				em->ops->destroy(tp, em);
396			else if (!tcf_em_is_simple(em) && em->data)
397				kfree((void *) em->data);
398			module_put(em->ops->owner);
399		}
400	}
401
402	tree->hdr.nmatches = 0;
403	kfree(tree->matches);
404}
405
406/**
407 * tcf_em_tree_dump - dump ematch tree into a rtnl message
408 *
409 * @skb: skb holding the rtnl message
410 * @t: ematch tree to be dumped
411 * @tlv: TLV type to be used to encapsulate the tree
412 *
413 * This function dumps a ematch tree into a rtnl message. It is valid to
414 * call this function while the ematch tree is in use.
415 *
416 * Returns -1 if the skb tailroom is insufficient.
417 */
418int tcf_em_tree_dump(struct sk_buff *skb, struct tcf_ematch_tree *tree, int tlv)
419{
420	int i;
421	u8 *tail;
422	struct rtattr *top_start = (struct rtattr *)skb_tail_pointer(skb);
423	struct rtattr *list_start;
424
425	RTA_PUT(skb, tlv, 0, NULL);
426	RTA_PUT(skb, TCA_EMATCH_TREE_HDR, sizeof(tree->hdr), &tree->hdr);
427
428	list_start = (struct rtattr *)skb_tail_pointer(skb);
429	RTA_PUT(skb, TCA_EMATCH_TREE_LIST, 0, NULL);
430
431	tail = skb_tail_pointer(skb);
432	for (i = 0; i < tree->hdr.nmatches; i++) {
433		struct rtattr *match_start = (struct rtattr *)tail;
434		struct tcf_ematch *em = tcf_em_get_match(tree, i);
435		struct tcf_ematch_hdr em_hdr = {
436			.kind = em->ops ? em->ops->kind : TCF_EM_CONTAINER,
437			.matchid = em->matchid,
438			.flags = em->flags
439		};
440
441		RTA_PUT(skb, i+1, sizeof(em_hdr), &em_hdr);
442
443		if (em->ops && em->ops->dump) {
444			if (em->ops->dump(skb, em) < 0)
445				goto rtattr_failure;
446		} else if (tcf_em_is_container(em) || tcf_em_is_simple(em)) {
447			u32 u = em->data;
448			RTA_PUT_NOHDR(skb, sizeof(u), &u);
449		} else if (em->datalen > 0)
450			RTA_PUT_NOHDR(skb, em->datalen, (void *) em->data);
451
452		tail = skb_tail_pointer(skb);
453		match_start->rta_len = tail - (u8 *)match_start;
454	}
455
456	list_start->rta_len = tail - (u8 *)list_start;
457	top_start->rta_len = tail - (u8 *)top_start;
458
459	return 0;
460
461rtattr_failure:
462	return -1;
463}
464
465static inline int tcf_em_match(struct sk_buff *skb, struct tcf_ematch *em,
466			       struct tcf_pkt_info *info)
467{
468	int r = em->ops->match(skb, em, info);
469	return tcf_em_is_inverted(em) ? !r : r;
470}
471
472/* Do not use this function directly, use tcf_em_tree_match instead */
473int __tcf_em_tree_match(struct sk_buff *skb, struct tcf_ematch_tree *tree,
474			struct tcf_pkt_info *info)
475{
476	int stackp = 0, match_idx = 0, res = 0;
477	struct tcf_ematch *cur_match;
478	int stack[CONFIG_NET_EMATCH_STACK];
479
480proceed:
481	while (match_idx < tree->hdr.nmatches) {
482		cur_match = tcf_em_get_match(tree, match_idx);
483
484		if (tcf_em_is_container(cur_match)) {
485			if (unlikely(stackp >= CONFIG_NET_EMATCH_STACK))
486				goto stack_overflow;
487
488			stack[stackp++] = match_idx;
489			match_idx = cur_match->data;
490			goto proceed;
491		}
492
493		res = tcf_em_match(skb, cur_match, info);
494
495		if (tcf_em_early_end(cur_match, res))
496			break;
497
498		match_idx++;
499	}
500
501pop_stack:
502	if (stackp > 0) {
503		match_idx = stack[--stackp];
504		cur_match = tcf_em_get_match(tree, match_idx);
505
506		if (tcf_em_early_end(cur_match, res))
507			goto pop_stack;
508		else {
509			match_idx++;
510			goto proceed;
511		}
512	}
513
514	return res;
515
516stack_overflow:
517	if (net_ratelimit())
518		printk("Local stack overflow, increase NET_EMATCH_STACK\n");
519	return -1;
520}
521
522EXPORT_SYMBOL(tcf_em_register);
523EXPORT_SYMBOL(tcf_em_unregister);
524EXPORT_SYMBOL(tcf_em_tree_validate);
525EXPORT_SYMBOL(tcf_em_tree_destroy);
526EXPORT_SYMBOL(tcf_em_tree_dump);
527EXPORT_SYMBOL(__tcf_em_tree_match);
528