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Linux/net/sched/ematch.c

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  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 
 93 static LIST_HEAD(ematch_ops);
 94 static DEFINE_RWLOCK(ematch_mod_lock);
 95 
 96 static 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  */
126 int 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;
141 errout:
142         write_unlock(&ematch_mod_lock);
143         return err;
144 }
145 EXPORT_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  */
158 void 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 }
164 EXPORT_SYMBOL(tcf_em_unregister);
165 
166 static 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 
173 static 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 = tp->chain->block->net;
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                                 em->ops = NULL;
232                                 err = -EAGAIN;
233                         }
234 #endif
235                         goto errout;
236                 }
237 
238                 /* ematch module provides expected length of data, so we
239                  * can do a basic sanity check.
240                  */
241                 if (em->ops->datalen && data_len < em->ops->datalen)
242                         goto errout;
243 
244                 if (em->ops->change) {
245                         err = em->ops->change(net, data, data_len, em);
246                         if (err < 0)
247                                 goto errout;
248                 } else if (data_len > 0) {
249                         /* ematch module doesn't provide an own change
250                          * procedure and expects us to allocate and copy
251                          * the ematch data.
252                          *
253                          * TCF_EM_SIMPLE may be specified stating that the
254                          * data only consists of a u32 integer and the module
255                          * does not expected a memory reference but rather
256                          * the value carried.
257                          */
258                         if (em_hdr->flags & TCF_EM_SIMPLE) {
259                                 if (data_len < sizeof(u32))
260                                         goto errout;
261                                 em->data = *(u32 *) data;
262                         } else {
263                                 void *v = kmemdup(data, data_len, GFP_KERNEL);
264                                 if (v == NULL) {
265                                         err = -ENOBUFS;
266                                         goto errout;
267                                 }
268                                 em->data = (unsigned long) v;
269                         }
270                 }
271         }
272 
273         em->matchid = em_hdr->matchid;
274         em->flags = em_hdr->flags;
275         em->datalen = data_len;
276         em->net = net;
277 
278         err = 0;
279 errout:
280         return err;
281 }
282 
283 static const struct nla_policy em_policy[TCA_EMATCH_TREE_MAX + 1] = {
284         [TCA_EMATCH_TREE_HDR]   = { .len = sizeof(struct tcf_ematch_tree_hdr) },
285         [TCA_EMATCH_TREE_LIST]  = { .type = NLA_NESTED },
286 };
287 
288 /**
289  * tcf_em_tree_validate - validate ematch config TLV and build ematch tree
290  *
291  * @tp: classifier kind handle
292  * @nla: ematch tree configuration TLV
293  * @tree: destination ematch tree variable to store the resulting
294  *        ematch tree.
295  *
296  * This function validates the given configuration TLV @nla and builds an
297  * ematch tree in @tree. The resulting tree must later be copied into
298  * the private classifier data using tcf_em_tree_change(). You MUST NOT
299  * provide the ematch tree variable of the private classifier data directly,
300  * the changes would not be locked properly.
301  *
302  * Returns a negative error code if the configuration TLV contains errors.
303  */
304 int tcf_em_tree_validate(struct tcf_proto *tp, struct nlattr *nla,
305                          struct tcf_ematch_tree *tree)
306 {
307         int idx, list_len, matches_len, err;
308         struct nlattr *tb[TCA_EMATCH_TREE_MAX + 1];
309         struct nlattr *rt_match, *rt_hdr, *rt_list;
310         struct tcf_ematch_tree_hdr *tree_hdr;
311         struct tcf_ematch *em;
312 
313         memset(tree, 0, sizeof(*tree));
314         if (!nla)
315                 return 0;
316 
317         err = nla_parse_nested(tb, TCA_EMATCH_TREE_MAX, nla, em_policy, NULL);
318         if (err < 0)
319                 goto errout;
320 
321         err = -EINVAL;
322         rt_hdr = tb[TCA_EMATCH_TREE_HDR];
323         rt_list = tb[TCA_EMATCH_TREE_LIST];
324 
325         if (rt_hdr == NULL || rt_list == NULL)
326                 goto errout;
327 
328         tree_hdr = nla_data(rt_hdr);
329         memcpy(&tree->hdr, tree_hdr, sizeof(*tree_hdr));
330 
331         rt_match = nla_data(rt_list);
332         list_len = nla_len(rt_list);
333         matches_len = tree_hdr->nmatches * sizeof(*em);
334 
335         tree->matches = kzalloc(matches_len, GFP_KERNEL);
336         if (tree->matches == NULL)
337                 goto errout;
338 
339         /* We do not use nla_parse_nested here because the maximum
340          * number of attributes is unknown. This saves us the allocation
341          * for a tb buffer which would serve no purpose at all.
342          *
343          * The array of rt attributes is parsed in the order as they are
344          * provided, their type must be incremental from 1 to n. Even
345          * if it does not serve any real purpose, a failure of sticking
346          * to this policy will result in parsing failure.
347          */
348         for (idx = 0; nla_ok(rt_match, list_len); idx++) {
349                 err = -EINVAL;
350 
351                 if (rt_match->nla_type != (idx + 1))
352                         goto errout_abort;
353 
354                 if (idx >= tree_hdr->nmatches)
355                         goto errout_abort;
356 
357                 if (nla_len(rt_match) < sizeof(struct tcf_ematch_hdr))
358                         goto errout_abort;
359 
360                 em = tcf_em_get_match(tree, idx);
361 
362                 err = tcf_em_validate(tp, tree_hdr, em, rt_match, idx);
363                 if (err < 0)
364                         goto errout_abort;
365 
366                 rt_match = nla_next(rt_match, &list_len);
367         }
368 
369         /* Check if the number of matches provided by userspace actually
370          * complies with the array of matches. The number was used for
371          * the validation of references and a mismatch could lead to
372          * undefined references during the matching process.
373          */
374         if (idx != tree_hdr->nmatches) {
375                 err = -EINVAL;
376                 goto errout_abort;
377         }
378 
379         err = 0;
380 errout:
381         return err;
382 
383 errout_abort:
384         tcf_em_tree_destroy(tree);
385         return err;
386 }
387 EXPORT_SYMBOL(tcf_em_tree_validate);
388 
389 /**
390  * tcf_em_tree_destroy - destroy an ematch tree
391  *
392  * @tp: classifier kind handle
393  * @tree: ematch tree to be deleted
394  *
395  * This functions destroys an ematch tree previously created by
396  * tcf_em_tree_validate()/tcf_em_tree_change(). You must ensure that
397  * the ematch tree is not in use before calling this function.
398  */
399 void tcf_em_tree_destroy(struct tcf_ematch_tree *tree)
400 {
401         int i;
402 
403         if (tree->matches == NULL)
404                 return;
405 
406         for (i = 0; i < tree->hdr.nmatches; i++) {
407                 struct tcf_ematch *em = tcf_em_get_match(tree, i);
408 
409                 if (em->ops) {
410                         if (em->ops->destroy)
411                                 em->ops->destroy(em);
412                         else if (!tcf_em_is_simple(em))
413                                 kfree((void *) em->data);
414                         module_put(em->ops->owner);
415                 }
416         }
417 
418         tree->hdr.nmatches = 0;
419         kfree(tree->matches);
420         tree->matches = NULL;
421 }
422 EXPORT_SYMBOL(tcf_em_tree_destroy);
423 
424 /**
425  * tcf_em_tree_dump - dump ematch tree into a rtnl message
426  *
427  * @skb: skb holding the rtnl message
428  * @t: ematch tree to be dumped
429  * @tlv: TLV type to be used to encapsulate the tree
430  *
431  * This function dumps a ematch tree into a rtnl message. It is valid to
432  * call this function while the ematch tree is in use.
433  *
434  * Returns -1 if the skb tailroom is insufficient.
435  */
436 int tcf_em_tree_dump(struct sk_buff *skb, struct tcf_ematch_tree *tree, int tlv)
437 {
438         int i;
439         u8 *tail;
440         struct nlattr *top_start;
441         struct nlattr *list_start;
442 
443         top_start = nla_nest_start(skb, tlv);
444         if (top_start == NULL)
445                 goto nla_put_failure;
446 
447         if (nla_put(skb, TCA_EMATCH_TREE_HDR, sizeof(tree->hdr), &tree->hdr))
448                 goto nla_put_failure;
449 
450         list_start = nla_nest_start(skb, TCA_EMATCH_TREE_LIST);
451         if (list_start == NULL)
452                 goto nla_put_failure;
453 
454         tail = skb_tail_pointer(skb);
455         for (i = 0; i < tree->hdr.nmatches; i++) {
456                 struct nlattr *match_start = (struct nlattr *)tail;
457                 struct tcf_ematch *em = tcf_em_get_match(tree, i);
458                 struct tcf_ematch_hdr em_hdr = {
459                         .kind = em->ops ? em->ops->kind : TCF_EM_CONTAINER,
460                         .matchid = em->matchid,
461                         .flags = em->flags
462                 };
463 
464                 if (nla_put(skb, i + 1, sizeof(em_hdr), &em_hdr))
465                         goto nla_put_failure;
466 
467                 if (em->ops && em->ops->dump) {
468                         if (em->ops->dump(skb, em) < 0)
469                                 goto nla_put_failure;
470                 } else if (tcf_em_is_container(em) || tcf_em_is_simple(em)) {
471                         u32 u = em->data;
472                         nla_put_nohdr(skb, sizeof(u), &u);
473                 } else if (em->datalen > 0)
474                         nla_put_nohdr(skb, em->datalen, (void *) em->data);
475 
476                 tail = skb_tail_pointer(skb);
477                 match_start->nla_len = tail - (u8 *)match_start;
478         }
479 
480         nla_nest_end(skb, list_start);
481         nla_nest_end(skb, top_start);
482 
483         return 0;
484 
485 nla_put_failure:
486         return -1;
487 }
488 EXPORT_SYMBOL(tcf_em_tree_dump);
489 
490 static inline int tcf_em_match(struct sk_buff *skb, struct tcf_ematch *em,
491                                struct tcf_pkt_info *info)
492 {
493         int r = em->ops->match(skb, em, info);
494 
495         return tcf_em_is_inverted(em) ? !r : r;
496 }
497 
498 /* Do not use this function directly, use tcf_em_tree_match instead */
499 int __tcf_em_tree_match(struct sk_buff *skb, struct tcf_ematch_tree *tree,
500                         struct tcf_pkt_info *info)
501 {
502         int stackp = 0, match_idx = 0, res = 0;
503         struct tcf_ematch *cur_match;
504         int stack[CONFIG_NET_EMATCH_STACK];
505 
506 proceed:
507         while (match_idx < tree->hdr.nmatches) {
508                 cur_match = tcf_em_get_match(tree, match_idx);
509 
510                 if (tcf_em_is_container(cur_match)) {
511                         if (unlikely(stackp >= CONFIG_NET_EMATCH_STACK))
512                                 goto stack_overflow;
513 
514                         stack[stackp++] = match_idx;
515                         match_idx = cur_match->data;
516                         goto proceed;
517                 }
518 
519                 res = tcf_em_match(skb, cur_match, info);
520 
521                 if (tcf_em_early_end(cur_match, res))
522                         break;
523 
524                 match_idx++;
525         }
526 
527 pop_stack:
528         if (stackp > 0) {
529                 match_idx = stack[--stackp];
530                 cur_match = tcf_em_get_match(tree, match_idx);
531 
532                 if (tcf_em_is_inverted(cur_match))
533                         res = !res;
534 
535                 if (tcf_em_early_end(cur_match, res)) {
536                         goto pop_stack;
537                 } else {
538                         match_idx++;
539                         goto proceed;
540                 }
541         }
542 
543         return res;
544 
545 stack_overflow:
546         net_warn_ratelimited("tc ematch: local stack overflow, increase NET_EMATCH_STACK\n");
547         return -1;
548 }
549 EXPORT_SYMBOL(__tcf_em_tree_match);
550 

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