/*
 * AppArmor security module
 *
 * This file contains AppArmor dfa based regular expression matching engine
 *
 * Copyright (C) 1998-2008 Novell/SUSE
 * Copyright 2009-2010 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"

/**
 * 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 kmalloc)
 */
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 = kvmalloc(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;
                        /* TODO: do check that DEF state recursion terminates */
                        if (BASE_TABLE(dfa)[i] + 255 >= trans_count) {
                                printk(KERN_ERR "AppArmor DFA next/check upper "
                                       "bounds error\n");
                                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[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[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[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[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[state] + equiv[(u8) c];
                if (check[pos] == state)
                        state = next[pos];
                else
                        state = def[state];
        } else {
                /* default is direct to next state */
                pos = base[state] + (u8) c;
                if (check[pos] == state)
                        state = next[pos];
                else
                        state = def[state];
        }

        return state;
}