1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * net/sched/ematch.c		Extended Match API
4 *
5 * Authors:	Thomas Graf <tgraf@suug.ch>
6 *
7 * ==========================================================================
8 *
9 * An extended match (ematch) is a small classification tool not worth
10 * writing a full classifier for. Ematches can be interconnected to form
11 * a logic expression and get attached to classifiers to extend their
12 * functionatlity.
13 *
14 * The userspace part transforms the logic expressions into an array
15 * consisting of multiple sequences of interconnected ematches separated
16 * by markers. Precedence is implemented by a special ematch kind
17 * referencing a sequence beyond the marker of the current sequence
18 * causing the current position in the sequence to be pushed onto a stack
19 * to allow the current position to be overwritten by the position referenced
20 * in the special ematch. Matching continues in the new sequence until a
21 * marker is reached causing the position to be restored from the stack.
22 *
23 * Example:
24 *          A AND (B1 OR B2) AND C AND D
25 *
26 *              ------->-PUSH-------
27 *    -->--    /         -->--      \   -->--
28 *   /     \  /         /     \      \ /     \
29 * +-------+-------+-------+-------+-------+--------+
30 * | A AND | B AND | C AND | D END | B1 OR | B2 END |
31 * +-------+-------+-------+-------+-------+--------+
32 *                    \                      /
33 *                     --------<-POP---------
34 *
35 * where B is a virtual ematch referencing to sequence starting with B1.
36 *
37 * ==========================================================================
38 *
39 * How to write an ematch in 60 seconds
40 * ------------------------------------
41 *
42 *   1) Provide a matcher function:
43 *      static int my_match(struct sk_buff *skb, struct tcf_ematch *m,
44 *                          struct tcf_pkt_info *info)
45 *      {
46 *      	struct mydata *d = (struct mydata *) m->data;
47 *
48 *      	if (...matching goes here...)
49 *      		return 1;
50 *      	else
51 *      		return 0;
52 *      }
53 *
54 *   2) Fill out a struct tcf_ematch_ops:
55 *      static struct tcf_ematch_ops my_ops = {
56 *      	.kind = unique id,
57 *      	.datalen = sizeof(struct mydata),
58 *      	.match = my_match,
59 *      	.owner = THIS_MODULE,
60 *      };
61 *
62 *   3) Register/Unregister your ematch:
63 *      static int __init init_my_ematch(void)
64 *      {
65 *      	return tcf_em_register(&my_ops);
66 *      }
67 *
68 *      static void __exit exit_my_ematch(void)
69 *      {
70 *      	tcf_em_unregister(&my_ops);
71 *      }
72 *
73 *      module_init(init_my_ematch);
74 *      module_exit(exit_my_ematch);
75 *
76 *   4) By now you should have two more seconds left, barely enough to
77 *      open up a beer to watch the compilation going.
78 */
79
80#include <linux/module.h>
81#include <linux/slab.h>
82#include <linux/types.h>
83#include <linux/kernel.h>
84#include <linux/errno.h>
85#include <linux/rtnetlink.h>
86#include <linux/skbuff.h>
87#include <net/pkt_cls.h>
88
89static LIST_HEAD(ematch_ops);
90static DEFINE_RWLOCK(ematch_mod_lock);
91
92static struct tcf_ematch_ops *tcf_em_lookup(u16 kind)
93{
94	struct tcf_ematch_ops *e = NULL;
95
96	read_lock(&ematch_mod_lock);
97	list_for_each_entry(e, &ematch_ops, link) {
98		if (kind == e->kind) {
99			if (!try_module_get(e->owner))
100				e = NULL;
101			read_unlock(&ematch_mod_lock);
102			return e;
103		}
104	}
105	read_unlock(&ematch_mod_lock);
106
107	return NULL;
108}
109
110/**
111 * tcf_em_register - register an extended match
112 *
113 * @ops: ematch operations lookup table
114 *
115 * This function must be called by ematches to announce their presence.
116 * The given @ops must have kind set to a unique identifier and the
117 * callback match() must be implemented. All other callbacks are optional
118 * and a fallback implementation is used instead.
119 *
120 * Returns -EEXISTS if an ematch of the same kind has already registered.
121 */
122int tcf_em_register(struct tcf_ematch_ops *ops)
123{
124	int err = -EEXIST;
125	struct tcf_ematch_ops *e;
126
127	if (ops->match == NULL)
128		return -EINVAL;
129
130	write_lock(&ematch_mod_lock);
131	list_for_each_entry(e, &ematch_ops, link)
132		if (ops->kind == e->kind)
133			goto errout;
134
135	list_add_tail(&ops->link, &ematch_ops);
136	err = 0;
137errout:
138	write_unlock(&ematch_mod_lock);
139	return err;
140}
141EXPORT_SYMBOL(tcf_em_register);
142
143/**
144 * tcf_em_unregister - unregister and extended match
145 *
146 * @ops: ematch operations lookup table
147 *
148 * This function must be called by ematches to announce their disappearance
149 * for examples when the module gets unloaded. The @ops parameter must be
150 * the same as the one used for registration.
151 *
152 * Returns -ENOENT if no matching ematch was found.
153 */
154void tcf_em_unregister(struct tcf_ematch_ops *ops)
155{
156	write_lock(&ematch_mod_lock);
157	list_del(&ops->link);
158	write_unlock(&ematch_mod_lock);
159}
160EXPORT_SYMBOL(tcf_em_unregister);
161
162static inline struct tcf_ematch *tcf_em_get_match(struct tcf_ematch_tree *tree,
163						  int index)
164{
165	return &tree->matches[index];
166}
167
168
169static int tcf_em_validate(struct tcf_proto *tp,
170			   struct tcf_ematch_tree_hdr *tree_hdr,
171			   struct tcf_ematch *em, struct nlattr *nla, int idx)
172{
173	int err = -EINVAL;
174	struct tcf_ematch_hdr *em_hdr = nla_data(nla);
175	int data_len = nla_len(nla) - sizeof(*em_hdr);
176	void *data = (void *) em_hdr + sizeof(*em_hdr);
177	struct net *net = tp->chain->block->net;
178
179	if (!TCF_EM_REL_VALID(em_hdr->flags))
180		goto errout;
181
182	if (em_hdr->kind == TCF_EM_CONTAINER) {
183		/* Special ematch called "container", carries an index
184		 * referencing an external ematch sequence.
185		 */
186		u32 ref;
187
188		if (data_len < sizeof(ref))
189			goto errout;
190		ref = *(u32 *) data;
191
192		if (ref >= tree_hdr->nmatches)
193			goto errout;
194
195		/* We do not allow backward jumps to avoid loops and jumps
196		 * to our own position are of course illegal.
197		 */
198		if (ref <= idx)
199			goto errout;
200
201
202		em->data = ref;
203	} else {
204		/* Note: This lookup will increase the module refcnt
205		 * of the ematch module referenced. In case of a failure,
206		 * a destroy function is called by the underlying layer
207		 * which automatically releases the reference again, therefore
208		 * the module MUST not be given back under any circumstances
209		 * here. Be aware, the destroy function assumes that the
210		 * module is held if the ops field is non zero.
211		 */
212		em->ops = tcf_em_lookup(em_hdr->kind);
213
214		if (em->ops == NULL) {
215			err = -ENOENT;
216#ifdef CONFIG_MODULES
217			__rtnl_unlock();
218			request_module("ematch-kind-%u", em_hdr->kind);
219			rtnl_lock();
220			em->ops = tcf_em_lookup(em_hdr->kind);
221			if (em->ops) {
222				/* We dropped the RTNL mutex in order to
223				 * perform the module load. Tell the caller
224				 * to replay the request.
225				 */
226				module_put(em->ops->owner);
227				em->ops = NULL;
228				err = -EAGAIN;
229			}
230#endif
231			goto errout;
232		}
233
234		/* ematch module provides expected length of data, so we
235		 * can do a basic sanity check.
236		 */
237		if (em->ops->datalen && data_len < em->ops->datalen)
238			goto errout;
239
240		if (em->ops->change) {
241			err = -EINVAL;
242			if (em_hdr->flags & TCF_EM_SIMPLE)
243				goto errout;
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 (em->ops->datalen > 0)
259					goto errout;
260				if (data_len < sizeof(u32))
261					goto errout;
262				em->data = *(u32 *) data;
263			} else {
264				void *v = kmemdup(data, data_len, GFP_KERNEL);
265				if (v == NULL) {
266					err = -ENOBUFS;
267					goto errout;
268				}
269				em->data = (unsigned long) v;
270			}
271			em->datalen = data_len;
272		}
273	}
274
275	em->matchid = em_hdr->matchid;
276	em->flags = em_hdr->flags;
277	em->net = net;
278
279	err = 0;
280errout:
281	return err;
282}
283
284static const struct nla_policy em_policy[TCA_EMATCH_TREE_MAX + 1] = {
285	[TCA_EMATCH_TREE_HDR]	= { .len = sizeof(struct tcf_ematch_tree_hdr) },
286	[TCA_EMATCH_TREE_LIST]	= { .type = NLA_NESTED },
287};
288
289/**
290 * tcf_em_tree_validate - validate ematch config TLV and build ematch tree
291 *
292 * @tp: classifier kind handle
293 * @nla: ematch tree configuration TLV
294 * @tree: destination ematch tree variable to store the resulting
295 *        ematch tree.
296 *
297 * This function validates the given configuration TLV @nla and builds an
298 * ematch tree in @tree. The resulting tree must later be copied into
299 * the private classifier data using tcf_em_tree_change(). You MUST NOT
300 * provide the ematch tree variable of the private classifier data directly,
301 * the changes would not be locked properly.
302 *
303 * Returns a negative error code if the configuration TLV contains errors.
304 */
305int tcf_em_tree_validate(struct tcf_proto *tp, struct nlattr *nla,
306			 struct tcf_ematch_tree *tree)
307{
308	int idx, list_len, matches_len, err;
309	struct nlattr *tb[TCA_EMATCH_TREE_MAX + 1];
310	struct nlattr *rt_match, *rt_hdr, *rt_list;
311	struct tcf_ematch_tree_hdr *tree_hdr;
312	struct tcf_ematch *em;
313
314	memset(tree, 0, sizeof(*tree));
315	if (!nla)
316		return 0;
317
318	err = nla_parse_nested_deprecated(tb, TCA_EMATCH_TREE_MAX, nla,
319					  em_policy, NULL);
320	if (err < 0)
321		goto errout;
322
323	err = -EINVAL;
324	rt_hdr = tb[TCA_EMATCH_TREE_HDR];
325	rt_list = tb[TCA_EMATCH_TREE_LIST];
326
327	if (rt_hdr == NULL || rt_list == NULL)
328		goto errout;
329
330	tree_hdr = nla_data(rt_hdr);
331	memcpy(&tree->hdr, tree_hdr, sizeof(*tree_hdr));
332
333	rt_match = nla_data(rt_list);
334	list_len = nla_len(rt_list);
335	matches_len = tree_hdr->nmatches * sizeof(*em);
336
337	tree->matches = kzalloc(matches_len, GFP_KERNEL);
338	if (tree->matches == NULL)
339		goto errout;
340
341	/* We do not use nla_parse_nested here because the maximum
342	 * number of attributes is unknown. This saves us the allocation
343	 * for a tb buffer which would serve no purpose at all.
344	 *
345	 * The array of rt attributes is parsed in the order as they are
346	 * provided, their type must be incremental from 1 to n. Even
347	 * if it does not serve any real purpose, a failure of sticking
348	 * to this policy will result in parsing failure.
349	 */
350	for (idx = 0; nla_ok(rt_match, list_len); idx++) {
351		err = -EINVAL;
352
353		if (rt_match->nla_type != (idx + 1))
354			goto errout_abort;
355
356		if (idx >= tree_hdr->nmatches)
357			goto errout_abort;
358
359		if (nla_len(rt_match) < sizeof(struct tcf_ematch_hdr))
360			goto errout_abort;
361
362		em = tcf_em_get_match(tree, idx);
363
364		err = tcf_em_validate(tp, tree_hdr, em, rt_match, idx);
365		if (err < 0)
366			goto errout_abort;
367
368		rt_match = nla_next(rt_match, &list_len);
369	}
370
371	/* Check if the number of matches provided by userspace actually
372	 * complies with the array of matches. The number was used for
373	 * the validation of references and a mismatch could lead to
374	 * undefined references during the matching process.
375	 */
376	if (idx != tree_hdr->nmatches) {
377		err = -EINVAL;
378		goto errout_abort;
379	}
380
381	err = 0;
382errout:
383	return err;
384
385errout_abort:
386	tcf_em_tree_destroy(tree);
387	return err;
388}
389EXPORT_SYMBOL(tcf_em_tree_validate);
390
391/**
392 * tcf_em_tree_destroy - destroy an ematch tree
393 *
394 * @tree: ematch tree to be deleted
395 *
396 * This functions destroys an ematch tree previously created by
397 * tcf_em_tree_validate()/tcf_em_tree_change(). You must ensure that
398 * the ematch tree is not in use before calling this function.
399 */
400void tcf_em_tree_destroy(struct tcf_ematch_tree *tree)
401{
402	int i;
403
404	if (tree->matches == NULL)
405		return;
406
407	for (i = 0; i < tree->hdr.nmatches; i++) {
408		struct tcf_ematch *em = tcf_em_get_match(tree, i);
409
410		if (em->ops) {
411			if (em->ops->destroy)
412				em->ops->destroy(em);
413			else if (!tcf_em_is_simple(em))
414				kfree((void *) em->data);
415			module_put(em->ops->owner);
416		}
417	}
418
419	tree->hdr.nmatches = 0;
420	kfree(tree->matches);
421	tree->matches = NULL;
422}
423EXPORT_SYMBOL(tcf_em_tree_destroy);
424
425/**
426 * tcf_em_tree_dump - dump ematch tree into a rtnl message
427 *
428 * @skb: skb holding the rtnl message
429 * @tree: ematch tree to be dumped
430 * @tlv: TLV type to be used to encapsulate the tree
431 *
432 * This function dumps a ematch tree into a rtnl message. It is valid to
433 * call this function while the ematch tree is in use.
434 *
435 * Returns -1 if the skb tailroom is insufficient.
436 */
437int tcf_em_tree_dump(struct sk_buff *skb, struct tcf_ematch_tree *tree, int tlv)
438{
439	int i;
440	u8 *tail;
441	struct nlattr *top_start;
442	struct nlattr *list_start;
443
444	top_start = nla_nest_start_noflag(skb, tlv);
445	if (top_start == NULL)
446		goto nla_put_failure;
447
448	if (nla_put(skb, TCA_EMATCH_TREE_HDR, sizeof(tree->hdr), &tree->hdr))
449		goto nla_put_failure;
450
451	list_start = nla_nest_start_noflag(skb, TCA_EMATCH_TREE_LIST);
452	if (list_start == NULL)
453		goto nla_put_failure;
454
455	tail = skb_tail_pointer(skb);
456	for (i = 0; i < tree->hdr.nmatches; i++) {
457		struct nlattr *match_start = (struct nlattr *)tail;
458		struct tcf_ematch *em = tcf_em_get_match(tree, i);
459		struct tcf_ematch_hdr em_hdr = {
460			.kind = em->ops ? em->ops->kind : TCF_EM_CONTAINER,
461			.matchid = em->matchid,
462			.flags = em->flags
463		};
464
465		if (nla_put(skb, i + 1, sizeof(em_hdr), &em_hdr))
466			goto nla_put_failure;
467
468		if (em->ops && em->ops->dump) {
469			if (em->ops->dump(skb, em) < 0)
470				goto nla_put_failure;
471		} else if (tcf_em_is_container(em) || tcf_em_is_simple(em)) {
472			u32 u = em->data;
473			nla_put_nohdr(skb, sizeof(u), &u);
474		} else if (em->datalen > 0)
475			nla_put_nohdr(skb, em->datalen, (void *) em->data);
476
477		tail = skb_tail_pointer(skb);
478		match_start->nla_len = tail - (u8 *)match_start;
479	}
480
481	nla_nest_end(skb, list_start);
482	nla_nest_end(skb, top_start);
483
484	return 0;
485
486nla_put_failure:
487	return -1;
488}
489EXPORT_SYMBOL(tcf_em_tree_dump);
490
491static inline int tcf_em_match(struct sk_buff *skb, struct tcf_ematch *em,
492			       struct tcf_pkt_info *info)
493{
494	int r = em->ops->match(skb, em, info);
495
496	return tcf_em_is_inverted(em) ? !r : r;
497}
498
499/* Do not use this function directly, use tcf_em_tree_match instead */
500int __tcf_em_tree_match(struct sk_buff *skb, struct tcf_ematch_tree *tree,
501			struct tcf_pkt_info *info)
502{
503	int stackp = 0, match_idx = 0, res = 0;
504	struct tcf_ematch *cur_match;
505	int stack[CONFIG_NET_EMATCH_STACK];
506
507proceed:
508	while (match_idx < tree->hdr.nmatches) {
509		cur_match = tcf_em_get_match(tree, match_idx);
510
511		if (tcf_em_is_container(cur_match)) {
512			if (unlikely(stackp >= CONFIG_NET_EMATCH_STACK))
513				goto stack_overflow;
514
515			stack[stackp++] = match_idx;
516			match_idx = cur_match->data;
517			goto proceed;
518		}
519
520		res = tcf_em_match(skb, cur_match, info);
521
522		if (tcf_em_early_end(cur_match, res))
523			break;
524
525		match_idx++;
526	}
527
528pop_stack:
529	if (stackp > 0) {
530		match_idx = stack[--stackp];
531		cur_match = tcf_em_get_match(tree, match_idx);
532
533		if (tcf_em_is_inverted(cur_match))
534			res = !res;
535
536		if (tcf_em_early_end(cur_match, res)) {
537			goto pop_stack;
538		} else {
539			match_idx++;
540			goto proceed;
541		}
542	}
543
544	return res;
545
546stack_overflow:
547	net_warn_ratelimited("tc ematch: local stack overflow, increase NET_EMATCH_STACK\n");
548	return -1;
549}
550EXPORT_SYMBOL(__tcf_em_tree_match);
551