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 
lookup_ts_algo(const char * name)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  */
textsearch_register(struct ts_ops * ops)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  */
textsearch_unregister(struct ts_ops * ops)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 
get_linear_data(unsigned int consumed,const u8 ** dst,struct ts_config * conf,struct ts_state * state)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  */
textsearch_find_continuous(struct ts_config * conf,struct ts_state * state,const void * data,unsigned int len)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  */
textsearch_prepare(const char * algo,const void * pattern,unsigned int len,gfp_t gfp_mask,int flags)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  */
textsearch_destroy(struct ts_config * conf)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);
324