the-tree/lib/textsearch.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * lib/textsearch.c Generic text search interface
0004  *
0005  * Authors: Thomas Graf <tgraf@suug.ch>
0006  *      Pablo Neira Ayuso <pablo@netfilter.org>
0007  *
0008  * ==========================================================================
0009  */
0010
0011 /**
0012  * DOC: ts_intro
0013  * INTRODUCTION
0014  *
0015  *   The textsearch infrastructure provides text searching facilities for
0016  *   both linear and non-linear data. Individual search algorithms are
0017  *   implemented in modules and chosen by the user.
0018  *
0019  * ARCHITECTURE
0020  *
0021  * .. code-block:: none
0022  *
0023  *     User
0024  *     +----------------+
0025  *     |        finish()|<--------------(6)-----------------+
0026  *     |get_next_block()|<--------------(5)---------------+ |
0027  *     |                |                     Algorithm   | |
0028  *     |                |                    +------------------------------+
0029  *     |                |                    |  init()   find()   destroy() |
0030  *     |                |                    +------------------------------+
0031  *     |                |       Core API           ^       ^          ^
0032  *     |                |      +---------------+  (2)     (4)        (8)
0033  *     |             (1)|----->| prepare()     |---+       |          |
0034  *     |             (3)|----->| find()/next() |-----------+          |
0035  *     |             (7)|----->| destroy()     |----------------------+
0036  *     +----------------+      +---------------+
0037  *
0038  *   (1) User configures a search by calling textsearch_prepare() specifying
0039  *       the search parameters such as the pattern and algorithm name.
0040  *   (2) Core requests the algorithm to allocate and initialize a search
0041  *       configuration according to the specified parameters.
0042  *   (3) User starts the search(es) by calling textsearch_find() or
0043  *       textsearch_next() to fetch subsequent occurrences. A state variable
0044  *       is provided to the algorithm to store persistent variables.
0045  *   (4) Core eventually resets the search offset and forwards the find()
0046  *       request to the algorithm.
0047  *   (5) Algorithm calls get_next_block() provided by the user continuously
0048  *       to fetch the data to be searched in block by block.
0049  *   (6) Algorithm invokes finish() after the last call to get_next_block
0050  *       to clean up any leftovers from get_next_block. (Optional)
0051  *   (7) User destroys the configuration by calling textsearch_destroy().
0052  *   (8) Core notifies the algorithm to destroy algorithm specific
0053  *       allocations. (Optional)
0054  *
0055  * USAGE
0056  *
0057  *   Before a search can be performed, a configuration must be created
0058  *   by calling textsearch_prepare() specifying the searching algorithm,
0059  *   the pattern to look for and flags. As a flag, you can set TS_IGNORECASE
0060  *   to perform case insensitive matching. But it might slow down
0061  *   performance of algorithm, so you should use it at own your risk.
0062  *   The returned configuration may then be used for an arbitrary
0063  *   amount of times and even in parallel as long as a separate struct
0064  *   ts_state variable is provided to every instance.
0065  *
0066  *   The actual search is performed by either calling
0067  *   textsearch_find_continuous() for linear data or by providing
0068  *   an own get_next_block() implementation and
0069  *   calling textsearch_find(). Both functions return
0070  *   the position of the first occurrence of the pattern or UINT_MAX if
0071  *   no match was found. Subsequent occurrences can be found by calling
0072  *   textsearch_next() regardless of the linearity of the data.
0073  *
0074  *   Once you're done using a configuration it must be given back via
0075  *   textsearch_destroy.
0076  *
0077  * EXAMPLE::
0078  *
0079  *   int pos;
0080  *   struct ts_config *conf;
0081  *   struct ts_state state;
0082  *   const char *pattern = "chicken";
0083  *   const char *example = "We dance the funky chicken";
0084  *
0085  *   conf = textsearch_prepare("kmp", pattern, strlen(pattern),
0086  *                             GFP_KERNEL, TS_AUTOLOAD);
0087  *   if (IS_ERR(conf)) {
0088  *       err = PTR_ERR(conf);
0089  *       goto errout;
0090  *   }
0091  *
0092  *   pos = textsearch_find_continuous(conf, &state, example, strlen(example));
0093  *   if (pos != UINT_MAX)
0094  *       panic("Oh my god, dancing chickens at %d\n", pos);
0095  *
0096  *   textsearch_destroy(conf);
0097  */
0098 /* ========================================================================== */
0099
0100 #include <linux/module.h>
0101 #include <linux/types.h>
0102 #include <linux/string.h>
0103 #include <linux/init.h>
0104 #include <linux/rculist.h>
0105 #include <linux/rcupdate.h>
0106 #include <linux/err.h>
0107 #include <linux/textsearch.h>
0108 #include <linux/slab.h>
0109
0110 static LIST_HEAD(ts_ops);
0111 static DEFINE_SPINLOCK(ts_mod_lock);
0112
0113 static inline struct ts_ops *lookup_ts_algo(const char *name)
0114 {
0115     struct ts_ops *o;
0116
0117     rcu_read_lock();
0118     list_for_each_entry_rcu(o, &ts_ops, list) {
0119         if (!strcmp(name, o->name)) {
0120             if (!try_module_get(o->owner))
0121                 o = NULL;
0122             rcu_read_unlock();
0123             return o;
0124         }
0125     }
0126     rcu_read_unlock();
0127
0128     return NULL;
0129 }
0130
0131 /**
0132  * textsearch_register - register a textsearch module
0133  * @ops: operations lookup table
0134  *
0135  * This function must be called by textsearch modules to announce
0136  * their presence. The specified &@ops must have %name set to a
0137  * unique identifier and the callbacks find(), init(), get_pattern(),
0138  * and get_pattern_len() must be implemented.
0139  *
0140  * Returns 0 or -EEXISTS if another module has already registered
0141  * with same name.
0142  */
0143 int textsearch_register(struct ts_ops *ops)
0144 {
0145     int err = -EEXIST;
0146     struct ts_ops *o;
0147
0148     if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
0149         ops->get_pattern == NULL || ops->get_pattern_len == NULL)
0150         return -EINVAL;
0151
0152     spin_lock(&ts_mod_lock);
0153     list_for_each_entry(o, &ts_ops, list) {
0154         if (!strcmp(ops->name, o->name))
0155             goto errout;
0156     }
0157
0158     list_add_tail_rcu(&ops->list, &ts_ops);
0159     err = 0;
0160 errout:
0161     spin_unlock(&ts_mod_lock);
0162     return err;
0163 }
0164 EXPORT_SYMBOL(textsearch_register);
0165
0166 /**
0167  * textsearch_unregister - unregister a textsearch module
0168  * @ops: operations lookup table
0169  *
0170  * This function must be called by textsearch modules to announce
0171  * their disappearance for examples when the module gets unloaded.
0172  * The &ops parameter must be the same as the one during the
0173  * registration.
0174  *
0175  * Returns 0 on success or -ENOENT if no matching textsearch
0176  * registration was found.
0177  */
0178 int textsearch_unregister(struct ts_ops *ops)
0179 {
0180     int err = 0;
0181     struct ts_ops *o;
0182
0183     spin_lock(&ts_mod_lock);
0184     list_for_each_entry(o, &ts_ops, list) {
0185         if (o == ops) {
0186             list_del_rcu(&o->list);
0187             goto out;
0188         }
0189     }
0190
0191     err = -ENOENT;
0192 out:
0193     spin_unlock(&ts_mod_lock);
0194     return err;
0195 }
0196 EXPORT_SYMBOL(textsearch_unregister);
0197
0198 struct ts_linear_state
0199 {
0200     unsigned int    len;
0201     const void  *data;
0202 };
0203
0204 static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
0205                     struct ts_config *conf,
0206                     struct ts_state *state)
0207 {
0208     struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
0209
0210     if (likely(consumed < st->len)) {
0211         *dst = st->data + consumed;
0212         return st->len - consumed;
0213     }
0214
0215     return 0;
0216 }
0217
0218 /**
0219  * textsearch_find_continuous - search a pattern in continuous/linear data
0220  * @conf: search configuration
0221  * @state: search state
0222  * @data: data to search in
0223  * @len: length of data
0224  *
0225  * A simplified version of textsearch_find() for continuous/linear data.
0226  * Call textsearch_next() to retrieve subsequent matches.
0227  *
0228  * Returns the position of first occurrence of the pattern or
0229  * %UINT_MAX if no occurrence was found.
0230  */
0231 unsigned int textsearch_find_continuous(struct ts_config *conf,
0232                     struct ts_state *state,
0233                     const void *data, unsigned int len)
0234 {
0235     struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
0236
0237     conf->get_next_block = get_linear_data;
0238     st->data = data;
0239     st->len = len;
0240
0241     return textsearch_find(conf, state);
0242 }
0243 EXPORT_SYMBOL(textsearch_find_continuous);
0244
0245 /**
0246  * textsearch_prepare - Prepare a search
0247  * @algo: name of search algorithm
0248  * @pattern: pattern data
0249  * @len: length of pattern
0250  * @gfp_mask: allocation mask
0251  * @flags: search flags
0252  *
0253  * Looks up the search algorithm module and creates a new textsearch
0254  * configuration for the specified pattern.
0255  *
0256  * Note: The format of the pattern may not be compatible between
0257  *       the various search algorithms.
0258  *
0259  * Returns a new textsearch configuration according to the specified
0260  * parameters or a ERR_PTR(). If a zero length pattern is passed, this
0261  * function returns EINVAL.
0262  */
0263 struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
0264                      unsigned int len, gfp_t gfp_mask, int flags)
0265 {
0266     int err = -ENOENT;
0267     struct ts_config *conf;
0268     struct ts_ops *ops;
0269
0270     if (len == 0)
0271         return ERR_PTR(-EINVAL);
0272
0273     ops = lookup_ts_algo(algo);
0274 #ifdef CONFIG_MODULES
0275     /*
0276      * Why not always autoload you may ask. Some users are
0277      * in a situation where requesting a module may deadlock,
0278      * especially when the module is located on a NFS mount.
0279      */
0280     if (ops == NULL && flags & TS_AUTOLOAD) {
0281         request_module("ts_%s", algo);
0282         ops = lookup_ts_algo(algo);
0283     }
0284 #endif
0285
0286     if (ops == NULL)
0287         goto errout;
0288
0289     conf = ops->init(pattern, len, gfp_mask, flags);
0290     if (IS_ERR(conf)) {
0291         err = PTR_ERR(conf);
0292         goto errout;
0293     }
0294
0295     conf->ops = ops;
0296     return conf;
0297
0298 errout:
0299     if (ops)
0300         module_put(ops->owner);
0301
0302     return ERR_PTR(err);
0303 }
0304 EXPORT_SYMBOL(textsearch_prepare);
0305
0306 /**
0307  * textsearch_destroy - destroy a search configuration
0308  * @conf: search configuration
0309  *
0310  * Releases all references of the configuration and frees
0311  * up the memory.
0312  */
0313 void textsearch_destroy(struct ts_config *conf)
0314 {
0315     if (conf->ops) {
0316         if (conf->ops->destroy)
0317             conf->ops->destroy(conf);
0318         module_put(conf->ops->owner);
0319     }
0320
0321     kfree(conf);
0322 }
0323 EXPORT_SYMBOL(textsearch_destroy);