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        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                                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;
 279errout:
 280        return err;
 281}
 282
 283static 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 */
 304int 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);
 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;
 380errout:
 381        return err;
 382
 383errout_abort:
 384        tcf_em_tree_destroy(tree);
 385        return err;
 386}
 387EXPORT_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 */
 399void 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}
 422EXPORT_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 */
 436int 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
 485nla_put_failure:
 486        return -1;
 487}
 488EXPORT_SYMBOL(tcf_em_tree_dump);
 489
 490static 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 */
 499int __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
 506proceed:
 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
 527pop_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
 545stack_overflow:
 546        net_warn_ratelimited("tc ematch: local stack overflow, increase NET_EMATCH_STACK\n");
 547        return -1;
 548}
 549EXPORT_SYMBOL(__tcf_em_tree_match);
 550