lib/textsearch.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * lib/textsearch.c     Generic text search interface
   4  *
   5  * Authors:     Thomas Graf <tgraf@suug.ch>
   6  *              Pablo Neira Ayuso <pablo@netfilter.org>
   7  *
   8  * ==========================================================================
   9  */
  10
  11 /**
  12  * DOC: ts_intro
  13  * INTRODUCTION
  14  *
  15  *   The textsearch infrastructure provides text searching facilities for
  16  *   both linear and non-linear data. Individual search algorithms are
  17  *   implemented in modules and chosen by the user.
  18  *
  19  * ARCHITECTURE
  20  *
  21  * .. code-block:: none
  22  *
  23  *     User
  24  *     +----------------+
  25  *     |        finish()|<--------------(6)-----------------+
  26  *     |get_next_block()|<--------------(5)---------------+ |
  27  *     |                |                     Algorithm   | |
  28  *     |                |                    +------------------------------+
  29  *     |                |                    |  init()   find()   destroy() |
  30  *     |                |                    +------------------------------+
  31  *     |                |       Core API           ^       ^          ^
  32  *     |                |      +---------------+  (2)     (4)        (8)
  33  *     |             (1)|----->| prepare()     |---+       |          |
  34  *     |             (3)|----->| find()/next() |-----------+          |
  35  *     |             (7)|----->| destroy()     |----------------------+
  36  *     +----------------+      +---------------+
  37  *
  38  *   (1) User configures a search by calling textsearch_prepare() specifying
  39  *       the search parameters such as the pattern and algorithm name.
  40  *   (2) Core requests the algorithm to allocate and initialize a search
  41  *       configuration according to the specified parameters.
  42  *   (3) User starts the search(es) by calling textsearch_find() or
  43  *       textsearch_next() to fetch subsequent occurrences. A state variable
  44  *       is provided to the algorithm to store persistent variables.
  45  *   (4) Core eventually resets the search offset and forwards the find()
  46  *       request to the algorithm.
  47  *   (5) Algorithm calls get_next_block() provided by the user continuously
  48  *       to fetch the data to be searched in block by block.
  49  *   (6) Algorithm invokes finish() after the last call to get_next_block
  50  *       to clean up any leftovers from get_next_block. (Optional)
  51  *   (7) User destroys the configuration by calling textsearch_destroy().
  52  *   (8) Core notifies the algorithm to destroy algorithm specific
  53  *       allocations. (Optional)
  54  *
  55  * USAGE
  56  *
  57  *   Before a search can be performed, a configuration must be created
  58  *   by calling textsearch_prepare() specifying the searching algorithm,
  59  *   the pattern to look for and flags. As a flag, you can set TS_IGNORECASE
  60  *   to perform case insensitive matching. But it might slow down
  61  *   performance of algorithm, so you should use it at own your risk.
  62  *   The returned configuration may then be used for an arbitrary
  63  *   amount of times and even in parallel as long as a separate struct
  64  *   ts_state variable is provided to every instance.
  65  *
  66  *   The actual search is performed by either calling
  67  *   textsearch_find_continuous() for linear data or by providing
  68  *   an own get_next_block() implementation and
  69  *   calling textsearch_find(). Both functions return
  70  *   the position of the first occurrence of the pattern or UINT_MAX if
  71  *   no match was found. Subsequent occurrences can be found by calling
  72  *   textsearch_next() regardless of the linearity of the data.
  73  *
  74  *   Once you're done using a configuration it must be given back via
  75  *   textsearch_destroy.
  76  *
  77  * EXAMPLE::
  78  *
  79  *   int pos;
  80  *   struct ts_config *conf;
  81  *   struct ts_state state;
  82  *   const char *pattern = "chicken";
  83  *   const char *example = "We dance the funky chicken";
  84  *
  85  *   conf = textsearch_prepare("kmp", pattern, strlen(pattern),
  86  *                             GFP_KERNEL, TS_AUTOLOAD);
  87  *   if (IS_ERR(conf)) {
  88  *       err = PTR_ERR(conf);
  89  *       goto errout;
  90  *   }
  91  *
  92  *   pos = textsearch_find_continuous(conf, \&state, example, strlen(example));
  93  *   if (pos != UINT_MAX)
  94  *       panic("Oh my god, dancing chickens at \%d\n", pos);
  95  *
  96  *   textsearch_destroy(conf);
  97  */
  98 /* ========================================================================== */
  99
 100 #include <linux/module.h>
 101 #include <linux/types.h>
 102 #include <linux/string.h>
 103 #include <linux/init.h>
 104 #include <linux/rculist.h>
 105 #include <linux/rcupdate.h>
 106 #include <linux/err.h>
 107 #include <linux/textsearch.h>
 108 #include <linux/slab.h>
 109
 110 static LIST_HEAD(ts_ops);
 111 static DEFINE_SPINLOCK(ts_mod_lock);
 112
 113 static inline struct ts_ops *lookup_ts_algo(const char *name)
 114 {
 115         struct ts_ops *o;
 116
 117         rcu_read_lock();
 118         list_for_each_entry_rcu(o, &ts_ops, list) {
 119                 if (!strcmp(name, o->name)) {
 120                         if (!try_module_get(o->owner))
 121                                 o = NULL;
 122                         rcu_read_unlock();
 123                         return o;
 124                 }
 125         }
 126         rcu_read_unlock();
 127
 128         return NULL;
 129 }
 130
 131 /**
 132  * textsearch_register - register a textsearch module
 133  * @ops: operations lookup table
 134  *
 135  * This function must be called by textsearch modules to announce
 136  * their presence. The specified &@ops must have %name set to a
 137  * unique identifier and the callbacks find(), init(), get_pattern(),
 138  * and get_pattern_len() must be implemented.
 139  *
 140  * Returns 0 or -EEXISTS if another module has already registered
 141  * with same name.
 142  */
 143 int textsearch_register(struct ts_ops *ops)
 144 {
 145         int err = -EEXIST;
 146         struct ts_ops *o;
 147
 148         if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
 149             ops->get_pattern == NULL || ops->get_pattern_len == NULL)
 150                 return -EINVAL;
 151
 152         spin_lock(&ts_mod_lock);
 153         list_for_each_entry(o, &ts_ops, list) {
 154                 if (!strcmp(ops->name, o->name))
 155                         goto errout;
 156         }
 157
 158         list_add_tail_rcu(&ops->list, &ts_ops);
 159         err = 0;
 160 errout:
 161         spin_unlock(&ts_mod_lock);
 162         return err;
 163 }
 164 EXPORT_SYMBOL(textsearch_register);
 165
 166 /**
 167  * textsearch_unregister - unregister a textsearch module
 168  * @ops: operations lookup table
 169  *
 170  * This function must be called by textsearch modules to announce
 171  * their disappearance for examples when the module gets unloaded.
 172  * The &ops parameter must be the same as the one during the
 173  * registration.
 174  *
 175  * Returns 0 on success or -ENOENT if no matching textsearch
 176  * registration was found.
 177  */
 178 int textsearch_unregister(struct ts_ops *ops)
 179 {
 180         int err = 0;
 181         struct ts_ops *o;
 182
 183         spin_lock(&ts_mod_lock);
 184         list_for_each_entry(o, &ts_ops, list) {
 185                 if (o == ops) {
 186                         list_del_rcu(&o->list);
 187                         goto out;
 188                 }
 189         }
 190
 191         err = -ENOENT;
 192 out:
 193         spin_unlock(&ts_mod_lock);
 194         return err;
 195 }
 196 EXPORT_SYMBOL(textsearch_unregister);
 197
 198 struct ts_linear_state
 199 {
 200         unsigned int    len;
 201         const void      *data;
 202 };
 203
 204 static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
 205                                     struct ts_config *conf,
 206                                     struct ts_state *state)
 207 {
 208         struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
 209
 210         if (likely(consumed < st->len)) {
 211                 *dst = st->data + consumed;
 212                 return st->len - consumed;
 213         }
 214
 215         return 0;
 216 }
 217
 218 /**
 219  * textsearch_find_continuous - search a pattern in continuous/linear data
 220  * @conf: search configuration
 221  * @state: search state
 222  * @data: data to search in
 223  * @len: length of data
 224  *
 225  * A simplified version of textsearch_find() for continuous/linear data.
 226  * Call textsearch_next() to retrieve subsequent matches.
 227  *
 228  * Returns the position of first occurrence of the pattern or
 229  * %UINT_MAX if no occurrence was found.
 230  */
 231 unsigned int textsearch_find_continuous(struct ts_config *conf,
 232                                         struct ts_state *state,
 233                                         const void *data, unsigned int len)
 234 {
 235         struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
 236
 237         conf->get_next_block = get_linear_data;
 238         st->data = data;
 239         st->len = len;
 240
 241         return textsearch_find(conf, state);
 242 }
 243 EXPORT_SYMBOL(textsearch_find_continuous);
 244
 245 /**
 246  * textsearch_prepare - Prepare a search
 247  * @algo: name of search algorithm
 248  * @pattern: pattern data
 249  * @len: length of pattern
 250  * @gfp_mask: allocation mask
 251  * @flags: search flags
 252  *
 253  * Looks up the search algorithm module and creates a new textsearch
 254  * configuration for the specified pattern.
 255  *
 256  * Note: The format of the pattern may not be compatible between
 257  *       the various search algorithms.
 258  *
 259  * Returns a new textsearch configuration according to the specified
 260  * parameters or a ERR_PTR(). If a zero length pattern is passed, this
 261  * function returns EINVAL.
 262  */
 263 struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
 264                                      unsigned int len, gfp_t gfp_mask, int flags)
 265 {
 266         int err = -ENOENT;
 267         struct ts_config *conf;
 268         struct ts_ops *ops;
 269
 270         if (len == 0)
 271                 return ERR_PTR(-EINVAL);
 272
 273         ops = lookup_ts_algo(algo);
 274 #ifdef CONFIG_MODULES
 275         /*
 276          * Why not always autoload you may ask. Some users are
 277          * in a situation where requesting a module may deadlock,
 278          * especially when the module is located on a NFS mount.
 279          */
 280         if (ops == NULL && flags & TS_AUTOLOAD) {
 281                 request_module("ts_%s", algo);
 282                 ops = lookup_ts_algo(algo);
 283         }
 284 #endif
 285
 286         if (ops == NULL)
 287                 goto errout;
 288
 289         conf = ops->init(pattern, len, gfp_mask, flags);
 290         if (IS_ERR(conf)) {
 291                 err = PTR_ERR(conf);
 292                 goto errout;
 293         }
 294
 295         conf->ops = ops;
 296         return conf;
 297
 298 errout:
 299         if (ops)
 300                 module_put(ops->owner);
 301
 302         return ERR_PTR(err);
 303 }
 304 EXPORT_SYMBOL(textsearch_prepare);
 305
 306 /**
 307  * textsearch_destroy - destroy a search configuration
 308  * @conf: search configuration
 309  *
 310  * Releases all references of the configuration and frees
 311  * up the memory.
 312  */
 313 void textsearch_destroy(struct ts_config *conf)
 314 {
 315         if (conf->ops) {
 316                 if (conf->ops->destroy)
 317                         conf->ops->destroy(conf);
 318                 module_put(conf->ops->owner);
 319         }
 320
 321         kfree(conf);
 322 }
 323 EXPORT_SYMBOL(textsearch_destroy);