/*
   * AppArmor security module
   *
   * This file contains AppArmor dfa based regular expression matching engine
   *
   * Copyright (C) 1998-2008 Novell/SUSE
   * Copyright 2009-2012 Canonical Ltd.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation, version 2 of the
   * License.
   */
  
  #include <linux/errno.h>
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <linux/vmalloc.h>
  #include <linux/err.h>
  #include <linux/kref.h>
  
  #include "include/apparmor.h"
  #include "include/match.h"
  
  #define base_idx(X) ((X) & 0xffffff)
  
  /**
   * unpack_table - unpack a dfa table (one of accept, default, base, next check)
   * @blob: data to unpack (NOT NULL)
   * @bsize: size of blob
   *
   * Returns: pointer to table else NULL on failure
   *
   * NOTE: must be freed by kvfree (not kfree)
   */
  static struct table_header *unpack_table(char *blob, size_t bsize)
  {
  	struct table_header *table = NULL;
  	struct table_header th;
  	size_t tsize;
  
  	if (bsize < sizeof(struct table_header))
  		goto out;
  
  	/* loaded td_id's start at 1, subtract 1 now to avoid doing
  	 * it every time we use td_id as an index
  	 */
  	th.td_id = be16_to_cpu(*(u16 *) (blob)) - 1;
  	th.td_flags = be16_to_cpu(*(u16 *) (blob + 2));
  	th.td_lolen = be32_to_cpu(*(u32 *) (blob + 8));
  	blob += sizeof(struct table_header);
  
  	if (!(th.td_flags == YYTD_DATA16 || th.td_flags == YYTD_DATA32 ||
  	      th.td_flags == YYTD_DATA8))
  		goto out;
  
  	tsize = table_size(th.td_lolen, th.td_flags);
  	if (bsize < tsize)
  		goto out;
  
  	table = kvzalloc(tsize);
  	if (table) {
  		*table = th;
  		if (th.td_flags == YYTD_DATA8)
  			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
  				     u8, byte_to_byte);
  		else if (th.td_flags == YYTD_DATA16)
  			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
  				     u16, be16_to_cpu);
  		else if (th.td_flags == YYTD_DATA32)
  			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
  				     u32, be32_to_cpu);
  		else
  			goto fail;
  	}
  
  out:
  	/* if table was vmalloced make sure the page tables are synced
  	 * before it is used, as it goes live to all cpus.
  	 */
  	if (is_vmalloc_addr(table))
  		vm_unmap_aliases();
  	return table;
  fail:
  	kvfree(table);
  	return NULL;
  }
  
  /**
   * verify_dfa - verify that transitions and states in the tables are in bounds.
   * @dfa: dfa to test  (NOT NULL)
   * @flags: flags controlling what type of accept table are acceptable
   *
   * Assumes dfa has gone through the first pass verification done by unpacking
   * NOTE: this does not valid accept table values
   *
   * Returns: %0 else error code on failure to verify
   */
  static int verify_dfa(struct aa_dfa *dfa, int flags)
  {
  	size_t i, state_count, trans_count;
  	int error = -EPROTO;
  
  	/* check that required tables exist */
  	if (!(dfa->tables[YYTD_ID_DEF] &&
  	      dfa->tables[YYTD_ID_BASE] &&
  	      dfa->tables[YYTD_ID_NXT] && dfa->tables[YYTD_ID_CHK]))
  		goto out;
  
  	/* accept.size == default.size == base.size */
  	state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
  	if (ACCEPT1_FLAGS(flags)) {
  		if (!dfa->tables[YYTD_ID_ACCEPT])
  			goto out;
  		if (state_count != dfa->tables[YYTD_ID_ACCEPT]->td_lolen)
  			goto out;
  	}
  	if (ACCEPT2_FLAGS(flags)) {
  		if (!dfa->tables[YYTD_ID_ACCEPT2])
  			goto out;
  		if (state_count != dfa->tables[YYTD_ID_ACCEPT2]->td_lolen)
  			goto out;
  	}
  	if (state_count != dfa->tables[YYTD_ID_DEF]->td_lolen)
  		goto out;
  
  	/* next.size == chk.size */
  	trans_count = dfa->tables[YYTD_ID_NXT]->td_lolen;
  	if (trans_count != dfa->tables[YYTD_ID_CHK]->td_lolen)
  		goto out;
  
  	/* if equivalence classes then its table size must be 256 */
  	if (dfa->tables[YYTD_ID_EC] &&
  	    dfa->tables[YYTD_ID_EC]->td_lolen != 256)
  		goto out;
  
  	if (flags & DFA_FLAG_VERIFY_STATES) {
  		for (i = 0; i < state_count; i++) {
  			if (DEFAULT_TABLE(dfa)[i] >= state_count)
  				goto out;
  			if (base_idx(BASE_TABLE(dfa)[i]) + 255 >= trans_count) {
  				printk(KERN_ERR "AppArmor DFA next/check upper "
  				       "bounds error
  ");
  				goto out;
  			}
  		}
  
  		for (i = 0; i < trans_count; i++) {
  			if (NEXT_TABLE(dfa)[i] >= state_count)
  				goto out;
  			if (CHECK_TABLE(dfa)[i] >= state_count)
  				goto out;
  		}
  	}
  
  	error = 0;
  out:
  	return error;
  }
  
  /**
   * dfa_free - free a dfa allocated by aa_dfa_unpack
   * @dfa: the dfa to free  (MAYBE NULL)
   *
   * Requires: reference count to dfa == 0
   */
  static void dfa_free(struct aa_dfa *dfa)
  {
  	if (dfa) {
  		int i;
  
  		for (i = 0; i < ARRAY_SIZE(dfa->tables); i++) {
  			kvfree(dfa->tables[i]);
  			dfa->tables[i] = NULL;
  		}
  		kfree(dfa);
  	}
  }
  
  /**
   * aa_dfa_free_kref - free aa_dfa by kref (called by aa_put_dfa)
   * @kr: kref callback for freeing of a dfa  (NOT NULL)
   */
  void aa_dfa_free_kref(struct kref *kref)
  {
  	struct aa_dfa *dfa = container_of(kref, struct aa_dfa, count);
  	dfa_free(dfa);
  }
  
  /**
   * aa_dfa_unpack - unpack the binary tables of a serialized dfa
   * @blob: aligned serialized stream of data to unpack  (NOT NULL)
   * @size: size of data to unpack
   * @flags: flags controlling what type of accept tables are acceptable
   *
   * Unpack a dfa that has been serialized.  To find information on the dfa
   * format look in Documentation/security/apparmor.txt
   * Assumes the dfa @blob stream has been aligned on a 8 byte boundary
   *
   * Returns: an unpacked dfa ready for matching or ERR_PTR on failure
   */
  struct aa_dfa *aa_dfa_unpack(void *blob, size_t size, int flags)
  {
  	int hsize;
  	int error = -ENOMEM;
  	char *data = blob;
  	struct table_header *table = NULL;
  	struct aa_dfa *dfa = kzalloc(sizeof(struct aa_dfa), GFP_KERNEL);
  	if (!dfa)
  		goto fail;
  
  	kref_init(&dfa->count);
  
  	error = -EPROTO;
  
  	/* get dfa table set header */
  	if (size < sizeof(struct table_set_header))
  		goto fail;
  
  	if (ntohl(*(u32 *) data) != YYTH_MAGIC)
  		goto fail;
  
  	hsize = ntohl(*(u32 *) (data + 4));
  	if (size < hsize)
  		goto fail;
  
  	dfa->flags = ntohs(*(u16 *) (data + 12));
  	data += hsize;
  	size -= hsize;
  
  	while (size > 0) {
  		table = unpack_table(data, size);
  		if (!table)
  			goto fail;
  
  		switch (table->td_id) {
  		case YYTD_ID_ACCEPT:
  			if (!(table->td_flags & ACCEPT1_FLAGS(flags)))
  				goto fail;
  			break;
  		case YYTD_ID_ACCEPT2:
  			if (!(table->td_flags & ACCEPT2_FLAGS(flags)))
  				goto fail;
  			break;
  		case YYTD_ID_BASE:
  			if (table->td_flags != YYTD_DATA32)
  				goto fail;
  			break;
  		case YYTD_ID_DEF:
  		case YYTD_ID_NXT:
  		case YYTD_ID_CHK:
  			if (table->td_flags != YYTD_DATA16)
  				goto fail;
  			break;
  		case YYTD_ID_EC:
  			if (table->td_flags != YYTD_DATA8)
  				goto fail;
  			break;
  		default:
  			goto fail;
  		}
  		/* check for duplicate table entry */
  		if (dfa->tables[table->td_id])
  			goto fail;
  		dfa->tables[table->td_id] = table;
  		data += table_size(table->td_lolen, table->td_flags);
  		size -= table_size(table->td_lolen, table->td_flags);
  		table = NULL;
  	}
  
  	error = verify_dfa(dfa, flags);
  	if (error)
  		goto fail;
  
  	return dfa;
  
  fail:
  	kvfree(table);
  	dfa_free(dfa);
  	return ERR_PTR(error);
  }
  
  /**
   * aa_dfa_match_len - traverse @dfa to find state @str stops at
   * @dfa: the dfa to match @str against  (NOT NULL)
   * @start: the state of the dfa to start matching in
   * @str: the string of bytes to match against the dfa  (NOT NULL)
   * @len: length of the string of bytes to match
   *
   * aa_dfa_match_len will match @str against the dfa and return the state it
   * finished matching in. The final state can be used to look up the accepting
   * label, or as the start state of a continuing match.
   *
   * This function will happily match again the 0 byte and only finishes
   * when @len input is consumed.
   *
   * Returns: final state reached after input is consumed
   */
  unsigned int aa_dfa_match_len(struct aa_dfa *dfa, unsigned int start,
  			      const char *str, int len)
  {
  	u16 *def = DEFAULT_TABLE(dfa);
  	u32 *base = BASE_TABLE(dfa);
  	u16 *next = NEXT_TABLE(dfa);
  	u16 *check = CHECK_TABLE(dfa);
  	unsigned int state = start, pos;
  
  	if (state == 0)
  		return 0;
  
  	/* current state is <state>, matching character *str */
  	if (dfa->tables[YYTD_ID_EC]) {
  		/* Equivalence class table defined */
  		u8 *equiv = EQUIV_TABLE(dfa);
  		/* default is direct to next state */
  		for (; len; len--) {
  			pos = base_idx(base[state]) + equiv[(u8) *str++];
  			if (check[pos] == state)
  				state = next[pos];
  			else
  				state = def[state];
  		}
  	} else {
  		/* default is direct to next state */
  		for (; len; len--) {
  			pos = base_idx(base[state]) + (u8) *str++;
  			if (check[pos] == state)
  				state = next[pos];
  			else
  				state = def[state];
  		}
  	}
  
  	return state;
  }
  
  /**
   * aa_dfa_match - traverse @dfa to find state @str stops at
   * @dfa: the dfa to match @str against  (NOT NULL)
   * @start: the state of the dfa to start matching in
   * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
   *
   * aa_dfa_match will match @str against the dfa and return the state it
   * finished matching in. The final state can be used to look up the accepting
   * label, or as the start state of a continuing match.
   *
   * Returns: final state reached after input is consumed
   */
  unsigned int aa_dfa_match(struct aa_dfa *dfa, unsigned int start,
  			  const char *str)
  {
  	u16 *def = DEFAULT_TABLE(dfa);
  	u32 *base = BASE_TABLE(dfa);
  	u16 *next = NEXT_TABLE(dfa);
  	u16 *check = CHECK_TABLE(dfa);
  	unsigned int state = start, pos;
  
  	if (state == 0)
  		return 0;
  
  	/* current state is <state>, matching character *str */
  	if (dfa->tables[YYTD_ID_EC]) {
  		/* Equivalence class table defined */
  		u8 *equiv = EQUIV_TABLE(dfa);
  		/* default is direct to next state */
  		while (*str) {
  			pos = base_idx(base[state]) + equiv[(u8) *str++];
  			if (check[pos] == state)
  				state = next[pos];
  			else
  				state = def[state];
  		}
  	} else {
  		/* default is direct to next state */
  		while (*str) {
  			pos = base_idx(base[state]) + (u8) *str++;
  			if (check[pos] == state)
  				state = next[pos];
  			else
  				state = def[state];
  		}
  	}
  
  	return state;
  }
  
  /**
   * aa_dfa_next - step one character to the next state in the dfa
   * @dfa: the dfa to tranverse (NOT NULL)
   * @state: the state to start in
   * @c: the input character to transition on
   *
   * aa_dfa_match will step through the dfa by one input character @c
   *
   * Returns: state reach after input @c
   */
  unsigned int aa_dfa_next(struct aa_dfa *dfa, unsigned int state,
  			  const char c)
  {
  	u16 *def = DEFAULT_TABLE(dfa);
  	u32 *base = BASE_TABLE(dfa);
  	u16 *next = NEXT_TABLE(dfa);
  	u16 *check = CHECK_TABLE(dfa);
  	unsigned int pos;
  
  	/* current state is <state>, matching character *str */
  	if (dfa->tables[YYTD_ID_EC]) {
  		/* Equivalence class table defined */
  		u8 *equiv = EQUIV_TABLE(dfa);
  		/* default is direct to next state */
  
  		pos = base_idx(base[state]) + equiv[(u8) c];
  		if (check[pos] == state)
  			state = next[pos];
  		else
  			state = def[state];
  	} else {
  		/* default is direct to next state */
  		pos = base_idx(base[state]) + (u8) c;
  		if (check[pos] == state)
  			state = next[pos];
  		else
  			state = def[state];
  	}
  
  	return state;
  }