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+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * lib/textsearch.c Generic text search interface
+ *
+ * Authors: Thomas Graf <tgraf@suug.ch>
+ * Pablo Neira Ayuso <pablo@netfilter.org>
+ *
+ * ==========================================================================
+ */
+
+/**
+ * DOC: ts_intro
+ * INTRODUCTION
+ *
+ * The textsearch infrastructure provides text searching facilities for
+ * both linear and non-linear data. Individual search algorithms are
+ * implemented in modules and chosen by the user.
+ *
+ * ARCHITECTURE
+ *
+ * .. code-block:: none
+ *
+ * User
+ * +----------------+
+ * | finish()|<--------------(6)-----------------+
+ * |get_next_block()|<--------------(5)---------------+ |
+ * | | Algorithm | |
+ * | | +------------------------------+
+ * | | | init() find() destroy() |
+ * | | +------------------------------+
+ * | | Core API ^ ^ ^
+ * | | +---------------+ (2) (4) (8)
+ * | (1)|----->| prepare() |---+ | |
+ * | (3)|----->| find()/next() |-----------+ |
+ * | (7)|----->| destroy() |----------------------+
+ * +----------------+ +---------------+
+ *
+ * (1) User configures a search by calling textsearch_prepare() specifying
+ * the search parameters such as the pattern and algorithm name.
+ * (2) Core requests the algorithm to allocate and initialize a search
+ * configuration according to the specified parameters.
+ * (3) User starts the search(es) by calling textsearch_find() or
+ * textsearch_next() to fetch subsequent occurrences. A state variable
+ * is provided to the algorithm to store persistent variables.
+ * (4) Core eventually resets the search offset and forwards the find()
+ * request to the algorithm.
+ * (5) Algorithm calls get_next_block() provided by the user continuously
+ * to fetch the data to be searched in block by block.
+ * (6) Algorithm invokes finish() after the last call to get_next_block
+ * to clean up any leftovers from get_next_block. (Optional)
+ * (7) User destroys the configuration by calling textsearch_destroy().
+ * (8) Core notifies the algorithm to destroy algorithm specific
+ * allocations. (Optional)
+ *
+ * USAGE
+ *
+ * Before a search can be performed, a configuration must be created
+ * by calling textsearch_prepare() specifying the searching algorithm,
+ * the pattern to look for and flags. As a flag, you can set TS_IGNORECASE
+ * to perform case insensitive matching. But it might slow down
+ * performance of algorithm, so you should use it at own your risk.
+ * The returned configuration may then be used for an arbitrary
+ * amount of times and even in parallel as long as a separate struct
+ * ts_state variable is provided to every instance.
+ *
+ * The actual search is performed by either calling
+ * textsearch_find_continuous() for linear data or by providing
+ * an own get_next_block() implementation and
+ * calling textsearch_find(). Both functions return
+ * the position of the first occurrence of the pattern or UINT_MAX if
+ * no match was found. Subsequent occurrences can be found by calling
+ * textsearch_next() regardless of the linearity of the data.
+ *
+ * Once you're done using a configuration it must be given back via
+ * textsearch_destroy.
+ *
+ * EXAMPLE::
+ *
+ * int pos;
+ * struct ts_config *conf;
+ * struct ts_state state;
+ * const char *pattern = "chicken";
+ * const char *example = "We dance the funky chicken";
+ *
+ * conf = textsearch_prepare("kmp", pattern, strlen(pattern),
+ * GFP_KERNEL, TS_AUTOLOAD);
+ * if (IS_ERR(conf)) {
+ * err = PTR_ERR(conf);
+ * goto errout;
+ * }
+ *
+ * pos = textsearch_find_continuous(conf, &state, example, strlen(example));
+ * if (pos != UINT_MAX)
+ * panic("Oh my god, dancing chickens at %d\n", pos);
+ *
+ * textsearch_destroy(conf);
+ */
+/* ========================================================================== */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/init.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>
+#include <linux/err.h>
+#include <linux/textsearch.h>
+#include <linux/slab.h>
+
+static LIST_HEAD(ts_ops);
+static DEFINE_SPINLOCK(ts_mod_lock);
+
+static inline struct ts_ops *lookup_ts_algo(const char *name)
+{
+ struct ts_ops *o;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(o, &ts_ops, list) {
+ if (!strcmp(name, o->name)) {
+ if (!try_module_get(o->owner))
+ o = NULL;
+ rcu_read_unlock();
+ return o;
+ }
+ }
+ rcu_read_unlock();
+
+ return NULL;
+}
+
+/**
+ * textsearch_register - register a textsearch module
+ * @ops: operations lookup table
+ *
+ * This function must be called by textsearch modules to announce
+ * their presence. The specified &@ops must have %name set to a
+ * unique identifier and the callbacks find(), init(), get_pattern(),
+ * and get_pattern_len() must be implemented.
+ *
+ * Returns 0 or -EEXISTS if another module has already registered
+ * with same name.
+ */
+int textsearch_register(struct ts_ops *ops)
+{
+ int err = -EEXIST;
+ struct ts_ops *o;
+
+ if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
+ ops->get_pattern == NULL || ops->get_pattern_len == NULL)
+ return -EINVAL;
+
+ spin_lock(&ts_mod_lock);
+ list_for_each_entry(o, &ts_ops, list) {
+ if (!strcmp(ops->name, o->name))
+ goto errout;
+ }
+
+ list_add_tail_rcu(&ops->list, &ts_ops);
+ err = 0;
+errout:
+ spin_unlock(&ts_mod_lock);
+ return err;
+}
+EXPORT_SYMBOL(textsearch_register);
+
+/**
+ * textsearch_unregister - unregister a textsearch module
+ * @ops: operations lookup table
+ *
+ * This function must be called by textsearch modules to announce
+ * their disappearance for examples when the module gets unloaded.
+ * The &ops parameter must be the same as the one during the
+ * registration.
+ *
+ * Returns 0 on success or -ENOENT if no matching textsearch
+ * registration was found.
+ */
+int textsearch_unregister(struct ts_ops *ops)
+{
+ int err = 0;
+ struct ts_ops *o;
+
+ spin_lock(&ts_mod_lock);
+ list_for_each_entry(o, &ts_ops, list) {
+ if (o == ops) {
+ list_del_rcu(&o->list);
+ goto out;
+ }
+ }
+
+ err = -ENOENT;
+out:
+ spin_unlock(&ts_mod_lock);
+ return err;
+}
+EXPORT_SYMBOL(textsearch_unregister);
+
+struct ts_linear_state
+{
+ unsigned int len;
+ const void *data;
+};
+
+static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
+ struct ts_config *conf,
+ struct ts_state *state)
+{
+ struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
+
+ if (likely(consumed < st->len)) {
+ *dst = st->data + consumed;
+ return st->len - consumed;
+ }
+
+ return 0;
+}
+
+/**
+ * textsearch_find_continuous - search a pattern in continuous/linear data
+ * @conf: search configuration
+ * @state: search state
+ * @data: data to search in
+ * @len: length of data
+ *
+ * A simplified version of textsearch_find() for continuous/linear data.
+ * Call textsearch_next() to retrieve subsequent matches.
+ *
+ * Returns the position of first occurrence of the pattern or
+ * %UINT_MAX if no occurrence was found.
+ */
+unsigned int textsearch_find_continuous(struct ts_config *conf,
+ struct ts_state *state,
+ const void *data, unsigned int len)
+{
+ struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
+
+ conf->get_next_block = get_linear_data;
+ st->data = data;
+ st->len = len;
+
+ return textsearch_find(conf, state);
+}
+EXPORT_SYMBOL(textsearch_find_continuous);
+
+/**
+ * textsearch_prepare - Prepare a search
+ * @algo: name of search algorithm
+ * @pattern: pattern data
+ * @len: length of pattern
+ * @gfp_mask: allocation mask
+ * @flags: search flags
+ *
+ * Looks up the search algorithm module and creates a new textsearch
+ * configuration for the specified pattern.
+ *
+ * Note: The format of the pattern may not be compatible between
+ * the various search algorithms.
+ *
+ * Returns a new textsearch configuration according to the specified
+ * parameters or a ERR_PTR(). If a zero length pattern is passed, this
+ * function returns EINVAL.
+ */
+struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
+ unsigned int len, gfp_t gfp_mask, int flags)
+{
+ int err = -ENOENT;
+ struct ts_config *conf;
+ struct ts_ops *ops;
+
+ if (len == 0)
+ return ERR_PTR(-EINVAL);
+
+ ops = lookup_ts_algo(algo);
+#ifdef CONFIG_MODULES
+ /*
+ * Why not always autoload you may ask. Some users are
+ * in a situation where requesting a module may deadlock,
+ * especially when the module is located on a NFS mount.
+ */
+ if (ops == NULL && flags & TS_AUTOLOAD) {
+ request_module("ts_%s", algo);
+ ops = lookup_ts_algo(algo);
+ }
+#endif
+
+ if (ops == NULL)
+ goto errout;
+
+ conf = ops->init(pattern, len, gfp_mask, flags);
+ if (IS_ERR(conf)) {
+ err = PTR_ERR(conf);
+ goto errout;
+ }
+
+ conf->ops = ops;
+ return conf;
+
+errout:
+ if (ops)
+ module_put(ops->owner);
+
+ return ERR_PTR(err);
+}
+EXPORT_SYMBOL(textsearch_prepare);
+
+/**
+ * textsearch_destroy - destroy a search configuration
+ * @conf: search configuration
+ *
+ * Releases all references of the configuration and frees
+ * up the memory.
+ */
+void textsearch_destroy(struct ts_config *conf)
+{
+ if (conf->ops) {
+ if (conf->ops->destroy)
+ conf->ops->destroy(conf);
+ module_put(conf->ops->owner);
+ }
+
+ kfree(conf);
+}
+EXPORT_SYMBOL(textsearch_destroy);
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