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
  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
 182        if (!TCF_EM_REL_VALID(em_hdr->flags))
 183                goto errout;
 184
 185        if (em_hdr->kind == TCF_EM_CONTAINER) {
 186                /* Special ematch called "container", carries an index
 187                 * referencing an external ematch sequence.
 188                 */
 189                u32 ref;
 190
 191                if (data_len < sizeof(ref))
 192                        goto errout;
 193                ref = *(u32 *) data;
 194
 195                if (ref >= tree_hdr->nmatches)
 196                        goto errout;
 197
 198                /* We do not allow backward jumps to avoid loops and jumps
 199                 * to our own position are of course illegal.
 200                 */
 201                if (ref <= idx)
 202                        goto errout;
 203
 204
 205                em->data = ref;
 206        } else {
 207                /* Note: This lookup will increase the module refcnt
 208                 * of the ematch module referenced. In case of a failure,
 209                 * a destroy function is called by the underlying layer
 210                 * which automatically releases the reference again, therefore
 211                 * the module MUST not be given back under any circumstances
 212                 * here. Be aware, the destroy function assumes that the
 213                 * module is held if the ops field is non zero.
 214                 */
 215                em->ops = tcf_em_lookup(em_hdr->kind);
 216
 217                if (em->ops == NULL) {
 218                        err = -ENOENT;
 219#ifdef CONFIG_MODULES
 220                        __rtnl_unlock();
 221                        request_module("ematch-kind-%u", em_hdr->kind);
 222                        rtnl_lock();
 223                        em->ops = tcf_em_lookup(em_hdr->kind);
 224                        if (em->ops) {
 225                                /* We dropped the RTNL mutex in order to
 226                                 * perform the module load. Tell the caller
 227                                 * to replay the request.
 228                                 */
 229                                module_put(em->ops->owner);
 230                                err = -EAGAIN;
 231                        }
 232#endif
 233                        goto errout;
 234                }
 235
 236                /* ematch module provides expected length of data, so we
 237                 * can do a basic sanity check.
 238                 */
 239                if (em->ops->datalen && data_len < em->ops->datalen)
 240                        goto errout;
 241
 242                if (em->ops->change) {
 243                        err = em->ops->change(tp, data, data_len, em);
 244                        if (err < 0)
 245                                goto errout;
 246                } else if (data_len > 0) {
 247                        /* ematch module doesn't provide an own change
 248                         * procedure and expects us to allocate and copy
 249                         * the ematch data.
 250                         *
 251                         * TCF_EM_SIMPLE may be specified stating that the
 252                         * data only consists of a u32 integer and the module
 253                         * does not expected a memory reference but rather
 254                         * the value carried.
 255                         */
 256                        if (em_hdr->flags & TCF_EM_SIMPLE) {
 257                                if (data_len < sizeof(u32))
 258                                        goto errout;
 259                                em->data = *(u32 *) data;
 260                        } else {
 261                                void *v = kmemdup(data, data_len, GFP_KERNEL);
 262                                if (v == NULL) {
 263                                        err = -ENOBUFS;
 264                                        goto errout;
 265                                }
 266                                em->data = (unsigned long) v;
 267                        }
 268                }
 269        }
 270
 271        em->matchid = em_hdr->matchid;
 272        em->flags = em_hdr->flags;
 273        em->datalen = data_len;
 274
 275        err = 0;
 276errout:
 277        return err;
 278}
 279
 280static const struct nla_policy em_policy[TCA_EMATCH_TREE_MAX + 1] = {
 281        [TCA_EMATCH_TREE_HDR]   = { .len = sizeof(struct tcf_ematch_tree_hdr) },
 282        [TCA_EMATCH_TREE_LIST]  = { .type = NLA_NESTED },
 283};
 284
 285/**
 286 * tcf_em_tree_validate - validate ematch config TLV and build ematch tree
 287 *
 288 * @tp: classifier kind handle
 289 * @nla: ematch tree configuration TLV
 290 * @tree: destination ematch tree variable to store the resulting
 291 *        ematch tree.
 292 *
 293 * This function validates the given configuration TLV @nla and builds an
 294 * ematch tree in @tree. The resulting tree must later be copied into
 295 * the private classifier data using tcf_em_tree_change(). You MUST NOT
 296 * provide the ematch tree variable of the private classifier data directly,
 297 * the changes would not be locked properly.
 298 *
 299 * Returns a negative error code if the configuration TLV contains errors.
 300 */
 301int tcf_em_tree_validate(struct tcf_proto *tp, struct nlattr *nla,
 302                         struct tcf_ematch_tree *tree)
 303{
 304        int idx, list_len, matches_len, err;
 305        struct nlattr *tb[TCA_EMATCH_TREE_MAX + 1];
 306        struct nlattr *rt_match, *rt_hdr, *rt_list;
 307        struct tcf_ematch_tree_hdr *tree_hdr;
 308        struct tcf_ematch *em;
 309
 310        memset(tree, 0, sizeof(*tree));
 311        if (!nla)
 312                return 0;
 313
 314        err = nla_parse_nested(tb, TCA_EMATCH_TREE_MAX, nla, em_policy);
 315        if (err < 0)
 316                goto errout;
 317
 318        err = -EINVAL;
 319        rt_hdr = tb[TCA_EMATCH_TREE_HDR];
 320        rt_list = tb[TCA_EMATCH_TREE_LIST];
 321
 322        if (rt_hdr == NULL || rt_list == NULL)
 323                goto errout;
 324
 325        tree_hdr = nla_data(rt_hdr);
 326        memcpy(&tree->hdr, tree_hdr, sizeof(*tree_hdr));
 327
 328        rt_match = nla_data(rt_list);
 329        list_len = nla_len(rt_list);
 330        matches_len = tree_hdr->nmatches * sizeof(*em);
 331
 332        tree->matches = kzalloc(matches_len, GFP_KERNEL);
 333        if (tree->matches == NULL)
 334                goto errout;
 335
 336        /* We do not use nla_parse_nested here because the maximum
 337         * number of attributes is unknown. This saves us the allocation
 338         * for a tb buffer which would serve no purpose at all.
 339         *
 340         * The array of rt attributes is parsed in the order as they are
 341         * provided, their type must be incremental from 1 to n. Even
 342         * if it does not serve any real purpose, a failure of sticking
 343         * to this policy will result in parsing failure.
 344         */
 345        for (idx = 0; nla_ok(rt_match, list_len); idx++) {
 346                err = -EINVAL;
 347
 348                if (rt_match->nla_type != (idx + 1))
 349                        goto errout_abort;
 350
 351                if (idx >= tree_hdr->nmatches)
 352                        goto errout_abort;
 353
 354                if (nla_len(rt_match) < sizeof(struct tcf_ematch_hdr))
 355                        goto errout_abort;
 356
 357                em = tcf_em_get_match(tree, idx);
 358
 359                err = tcf_em_validate(tp, tree_hdr, em, rt_match, idx);
 360                if (err < 0)
 361                        goto errout_abort;
 362
 363                rt_match = nla_next(rt_match, &list_len);
 364        }
 365
 366        /* Check if the number of matches provided by userspace actually
 367         * complies with the array of matches. The number was used for
 368         * the validation of references and a mismatch could lead to
 369         * undefined references during the matching process.
 370         */
 371        if (idx != tree_hdr->nmatches) {
 372                err = -EINVAL;
 373                goto errout_abort;
 374        }
 375
 376        err = 0;
 377errout:
 378        return err;
 379
 380errout_abort:
 381        tcf_em_tree_destroy(tp, tree);
 382        return err;
 383}
 384EXPORT_SYMBOL(tcf_em_tree_validate);
 385
 386/**
 387 * tcf_em_tree_destroy - destroy an ematch tree
 388 *
 389 * @tp: classifier kind handle
 390 * @tree: ematch tree to be deleted
 391 *
 392 * This functions destroys an ematch tree previously created by
 393 * tcf_em_tree_validate()/tcf_em_tree_change(). You must ensure that
 394 * the ematch tree is not in use before calling this function.
 395 */
 396void tcf_em_tree_destroy(struct tcf_proto *tp, struct tcf_ematch_tree *tree)
 397{
 398        int i;
 399
 400        if (tree->matches == NULL)
 401                return;
 402
 403        for (i = 0; i < tree->hdr.nmatches; i++) {
 404                struct tcf_ematch *em = tcf_em_get_match(tree, i);
 405
 406                if (em->ops) {
 407                        if (em->ops->destroy)
 408                                em->ops->destroy(tp, em);
 409                        else if (!tcf_em_is_simple(em))
 410                                kfree((void *) em->data);
 411                        module_put(em->ops->owner);
 412                }
 413        }
 414
 415        tree->hdr.nmatches = 0;
 416        kfree(tree->matches);
 417        tree->matches = NULL;
 418}
 419EXPORT_SYMBOL(tcf_em_tree_destroy);
 420
 421/**
 422 * tcf_em_tree_dump - dump ematch tree into a rtnl message
 423 *
 424 * @skb: skb holding the rtnl message
 425 * @t: ematch tree to be dumped
 426 * @tlv: TLV type to be used to encapsulate the tree
 427 *
 428 * This function dumps a ematch tree into a rtnl message. It is valid to
 429 * call this function while the ematch tree is in use.
 430 *
 431 * Returns -1 if the skb tailroom is insufficient.
 432 */
 433int tcf_em_tree_dump(struct sk_buff *skb, struct tcf_ematch_tree *tree, int tlv)
 434{
 435        int i;
 436        u8 *tail;
 437        struct nlattr *top_start;
 438        struct nlattr *list_start;
 439
 440        top_start = nla_nest_start(skb, tlv);
 441        if (top_start == NULL)
 442                goto nla_put_failure;
 443
 444        if (nla_put(skb, TCA_EMATCH_TREE_HDR, sizeof(tree->hdr), &tree->hdr))
 445                goto nla_put_failure;
 446
 447        list_start = nla_nest_start(skb, TCA_EMATCH_TREE_LIST);
 448        if (list_start == NULL)
 449                goto nla_put_failure;
 450
 451        tail = skb_tail_pointer(skb);
 452        for (i = 0; i < tree->hdr.nmatches; i++) {
 453                struct nlattr *match_start = (struct nlattr *)tail;
 454                struct tcf_ematch *em = tcf_em_get_match(tree, i);
 455                struct tcf_ematch_hdr em_hdr = {
 456                        .kind = em->ops ? em->ops->kind : TCF_EM_CONTAINER,
 457                        .matchid = em->matchid,
 458                        .flags = em->flags
 459                };
 460
 461                if (nla_put(skb, i + 1, sizeof(em_hdr), &em_hdr))
 462                        goto nla_put_failure;
 463
 464                if (em->ops && em->ops->dump) {
 465                        if (em->ops->dump(skb, em) < 0)
 466                                goto nla_put_failure;
 467                } else if (tcf_em_is_container(em) || tcf_em_is_simple(em)) {
 468                        u32 u = em->data;
 469                        nla_put_nohdr(skb, sizeof(u), &u);
 470                } else if (em->datalen > 0)
 471                        nla_put_nohdr(skb, em->datalen, (void *) em->data);
 472
 473                tail = skb_tail_pointer(skb);
 474                match_start->nla_len = tail - (u8 *)match_start;
 475        }
 476
 477        nla_nest_end(skb, list_start);
 478        nla_nest_end(skb, top_start);
 479
 480        return 0;
 481
 482nla_put_failure:
 483        return -1;
 484}
 485EXPORT_SYMBOL(tcf_em_tree_dump);
 486
 487static inline int tcf_em_match(struct sk_buff *skb, struct tcf_ematch *em,
 488                               struct tcf_pkt_info *info)
 489{
 490        int r = em->ops->match(skb, em, info);
 491
 492        return tcf_em_is_inverted(em) ? !r : r;
 493}
 494
 495/* Do not use this function directly, use tcf_em_tree_match instead */
 496int __tcf_em_tree_match(struct sk_buff *skb, struct tcf_ematch_tree *tree,
 497                        struct tcf_pkt_info *info)
 498{
 499        int stackp = 0, match_idx = 0, res = 0;
 500        struct tcf_ematch *cur_match;
 501        int stack[CONFIG_NET_EMATCH_STACK];
 502
 503proceed:
 504        while (match_idx < tree->hdr.nmatches) {
 505                cur_match = tcf_em_get_match(tree, match_idx);
 506
 507                if (tcf_em_is_container(cur_match)) {
 508                        if (unlikely(stackp >= CONFIG_NET_EMATCH_STACK))
 509                                goto stack_overflow;
 510
 511                        stack[stackp++] = match_idx;
 512                        match_idx = cur_match->data;
 513                        goto proceed;
 514                }
 515
 516                res = tcf_em_match(skb, cur_match, info);
 517
 518                if (tcf_em_early_end(cur_match, res))
 519                        break;
 520
 521                match_idx++;
 522        }
 523
 524pop_stack:
 525        if (stackp > 0) {
 526                match_idx = stack[--stackp];
 527                cur_match = tcf_em_get_match(tree, match_idx);
 528
 529                if (tcf_em_early_end(cur_match, res))
 530                        goto pop_stack;
 531                else {
 532                        match_idx++;
 533                        goto proceed;
 534                }
 535        }
 536
 537        return res;
 538
 539stack_overflow:
 540        net_warn_ratelimited("tc ematch: local stack overflow, increase NET_EMATCH_STACK\n");
 541        return -1;
 542}
 543EXPORT_SYMBOL(__tcf_em_tree_match);
 544
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