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