/*
 * 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/lib.h"
#include "include/match.h"

#define base_idx(X) ((X) & 0xffffff)

static char nulldfa_src[] = {
        #include "nulldfa.in"
};
struct aa_dfa *nulldfa;

static char stacksplitdfa_src[] = {
        #include "stacksplitdfa.in"
};
struct aa_dfa *stacksplitdfa;

int aa_setup_dfa_engine(void)
{
        int error;

        nulldfa = aa_dfa_unpack(nulldfa_src, sizeof(nulldfa_src),
                                TO_ACCEPT1_FLAG(YYTD_DATA32) |
                                TO_ACCEPT2_FLAG(YYTD_DATA32));
        if (IS_ERR(nulldfa)) {
                error = PTR_ERR(nulldfa);
                nulldfa = NULL;
                return error;
        }

        stacksplitdfa = aa_dfa_unpack(stacksplitdfa_src,
                                      sizeof(stacksplitdfa_src),
                                      TO_ACCEPT1_FLAG(YYTD_DATA32) |
                                      TO_ACCEPT2_FLAG(YYTD_DATA32));
        if (IS_ERR(stacksplitdfa)) {
                aa_put_dfa(nulldfa);
                nulldfa = NULL;
                error = PTR_ERR(stacksplitdfa);
                stacksplitdfa = NULL;
                return error;
        }

        return 0;
}

void aa_teardown_dfa_engine(void)
{
        aa_put_dfa(stacksplitdfa);
        aa_put_dfa(nulldfa);
}

/**
 * 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(*(__be16 *) (blob)) - 1;
        if (th.td_id > YYTD_ID_MAX)
                goto out;
        th.td_flags = be16_to_cpu(*(__be16 *) (blob + 2));
        th.td_lolen = be32_to_cpu(*(__be32 *) (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, GFP_KERNEL);
        if (table) {
                table->td_id = th.td_id;
                table->td_flags = th.td_flags;
                table->td_lolen = th.td_lolen;
                if (th.td_flags == YYTD_DATA8)
                        UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
                                     u8, u8, byte_to_byte);
                else if (th.td_flags == YYTD_DATA16)
                        UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
                                     u16, __be16, be16_to_cpu);
                else if (th.td_flags == YYTD_DATA32)
                        UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
                                     u32, __be32, be32_to_cpu);
                else
                        goto fail;
                /* 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();
        }

out:
        return table;
fail:
        kvfree(table);
        return NULL;
}

/**
 * verify_table_headers - verify that the tables headers are as expected
 * @tables - array of dfa tables to check (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_table_headers(struct table_header **tables, int flags)
{
        size_t state_count, trans_count;
        int error = -EPROTO;

        /* check that required tables exist */
        if (!(tables[YYTD_ID_DEF] && tables[YYTD_ID_BASE] &&
              tables[YYTD_ID_NXT] && tables[YYTD_ID_CHK]))
                goto out;

        /* accept.size == default.size == base.size */
        state_count = tables[YYTD_ID_BASE]->td_lolen;
        if (ACCEPT1_FLAGS(flags)) {
                if (!tables[YYTD_ID_ACCEPT])
                        goto out;
                if (state_count != tables[YYTD_ID_ACCEPT]->td_lolen)
                        goto out;
        }
        if (ACCEPT2_FLAGS(flags)) {
                if (!tables[YYTD_ID_ACCEPT2])
                        goto out;
                if (state_count != tables[YYTD_ID_ACCEPT2]->td_lolen)
                        goto out;
        }
        if (state_count != tables[YYTD_ID_DEF]->td_lolen)
                goto out;

        /* next.size == chk.size */
        trans_count = tables[YYTD_ID_NXT]->td_lolen;
        if (trans_count != tables[YYTD_ID_CHK]->td_lolen)
                goto out;

        /* if equivalence classes then its table size must be 256 */
        if (tables[YYTD_ID_EC] && tables[YYTD_ID_EC]->td_lolen != 256)
                goto out;

        error = 0;
out:
        return error;
}

/**
 * verify_dfa - verify that transitions and states in the tables are in bounds.
 * @dfa: dfa to test  (NOT NULL)
 *
 * 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)
{
        size_t i, state_count, trans_count;
        int error = -EPROTO;

        state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
        trans_count = dfa->tables[YYTD_ID_NXT]->td_lolen;
        for (i = 0; i < state_count; i++) {
                if (!(BASE_TABLE(dfa)[i] & MATCH_FLAG_DIFF_ENCODE) &&
                    (DEFAULT_TABLE(dfa)[i] >= state_count))
                        goto out;
                if (base_idx(BASE_TABLE(dfa)[i]) + 255 >= trans_count) {
                        pr_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;
        }

        /* Now that all the other tables are verified, verify diffencoding */
        for (i = 0; i < state_count; i++) {
                size_t j, k;

                for (j = i;
                     (BASE_TABLE(dfa)[j] & MATCH_FLAG_DIFF_ENCODE) &&
                     !(BASE_TABLE(dfa)[j] & MARK_DIFF_ENCODE);
                     j = k) {
                        k = DEFAULT_TABLE(dfa)[j];
                        if (j == k)
                                goto out;
                        if (k < j)
                                break;          /* already verified */
                        BASE_TABLE(dfa)[j] |= MARK_DIFF_ENCODE;
                }
        }
        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/admin-guide/LSM/apparmor.rst
 * 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(*(__be32 *) data) != YYTH_MAGIC)
                goto fail;

        hsize = ntohl(*(__be32 *) (data + 4));
        if (size < hsize)
                goto fail;

        dfa->flags = ntohs(*(__be16 *) (data + 12));
        if (dfa->flags != 0 && dfa->flags != YYTH_FLAG_DIFF_ENCODE)
                goto fail;

        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_table_headers(dfa->tables, flags);
        if (error)
                goto fail;

        if (flags & DFA_FLAG_VERIFY_STATES) {
                error = verify_dfa(dfa);
                if (error)
                        goto fail;
        }

        return dfa;

fail:
        kvfree(table);
        dfa_free(dfa);
        return ERR_PTR(error);
}

#define match_char(state, def, base, next, check, C)    \
do {                                                    \
        u32 b = (base)[(state)];                        \
        unsigned int pos = base_idx(b) + (C);           \
        if ((check)[pos] != (state)) {                  \
                (state) = (def)[(state)];               \
                if (b & MATCH_FLAG_DIFF_ENCODE)         \
                        continue;                       \
                break;                                  \
        }                                               \
        (state) = (next)[pos];                          \
        break;                                          \
} while (1)

/**
 * 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;

        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);
                for (; len; len--)
                        match_char(state, def, base, next, check,
                                   equiv[(u8) *str++]);
        } else {
                /* default is direct to next state */
                for (; len; len--)
                        match_char(state, def, base, next, check, (u8) *str++);
        }

        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;

        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)
                        match_char(state, def, base, next, check,
                                   equiv[(u8) *str++]);
        } else {
                /* default is direct to next state */
                while (*str)
                        match_char(state, def, base, next, check, (u8) *str++);
        }

        return state;
}

/**
 * aa_dfa_next - step one character to the next state in the dfa
 * @dfa: the dfa to traverse (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);

        /* current state is <state>, matching character *str */
        if (dfa->tables[YYTD_ID_EC]) {
                /* Equivalence class table defined */
                u8 *equiv = EQUIV_TABLE(dfa);
                match_char(state, def, base, next, check, equiv[(u8) c]);
        } else
                match_char(state, def, base, next, check, (u8) c);

        return state;
}

/**
 * aa_dfa_match_until - traverse @dfa until accept state or end of input
 * @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)
 * @retpos: first character in str after match OR end of string
 *
 * 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_until(struct aa_dfa *dfa, unsigned int start,
                                const char *str, const char **retpos)
{
        u16 *def = DEFAULT_TABLE(dfa);
        u32 *base = BASE_TABLE(dfa);
        u16 *next = NEXT_TABLE(dfa);
        u16 *check = CHECK_TABLE(dfa);
        u32 *accept = ACCEPT_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];
                        if (accept[state])
                                break;
                }
        } 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];
                        if (accept[state])
                                break;
                }
        }

        *retpos = str;
        return state;
}

/**
 * aa_dfa_matchn_until - traverse @dfa until accept or @n bytes consumed
 * @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)
 * @n: length of the string of bytes to match
 * @retpos: first character in str after match OR str + n
 *
 * 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 @n input is consumed.
 *
 * Returns: final state reached after input is consumed
 */
unsigned int aa_dfa_matchn_until(struct aa_dfa *dfa, unsigned int start,
                                 const char *str, int n, const char **retpos)
{
        u16 *def = DEFAULT_TABLE(dfa);
        u32 *base = BASE_TABLE(dfa);
        u16 *next = NEXT_TABLE(dfa);
        u16 *check = CHECK_TABLE(dfa);
        u32 *accept = ACCEPT_TABLE(dfa);
        unsigned int state = start, pos;

        *retpos = NULL;
        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 (; n; n--) {
                        pos = base_idx(base[state]) + equiv[(u8) *str++];
                        if (check[pos] == state)
                                state = next[pos];
                        else
                                state = def[state];
                        if (accept[state])
                                break;
                }
        } else {
                /* default is direct to next state */
                for (; n; n--) {
                        pos = base_idx(base[state]) + (u8) *str++;
                        if (check[pos] == state)
                                state = next[pos];
                        else
                                state = def[state];
                        if (accept[state])
                                break;
                }
        }

        *retpos = str;
        return state;
}

#define inc_wb_pos(wb)                                          \
do {                                                            \
        wb->pos = (wb->pos + 1) & (wb->size - 1);               \
        wb->len = (wb->len + 1) & (wb->size - 1);               \
} while (0)

/* For DFAs that don't support extended tagging of states */
static bool is_loop(struct match_workbuf *wb, unsigned int state,
                    unsigned int *adjust)
{
        unsigned int pos = wb->pos;
        unsigned int i;

        if (wb->history[pos] < state)
                return false;

        for (i = 0; i <= wb->len; i++) {
                if (wb->history[pos] == state) {
                        *adjust = i;
                        return true;
                }
                if (pos == 0)
                        pos = wb->size;
                pos--;
        }

        *adjust = i;
        return true;
}

static unsigned int leftmatch_fb(struct aa_dfa *dfa, unsigned int start,
                                 const char *str, struct match_workbuf *wb,
                                 unsigned int *count)
{
        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;

        AA_BUG(!dfa);
        AA_BUG(!str);
        AA_BUG(!wb);
        AA_BUG(!count);

        *count = 0;
        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) {
                        unsigned int adjust;

                        wb->history[wb->pos] = state;
                        pos = base_idx(base[state]) + equiv[(u8) *str++];
                        if (check[pos] == state)
                                state = next[pos];
                        else
                                state = def[state];
                        if (is_loop(wb, state, &adjust)) {
                                state = aa_dfa_match(dfa, state, str);
                                *count -= adjust;
                                goto out;
                        }
                        inc_wb_pos(wb);
                        (*count)++;
                }
        } else {
                /* default is direct to next state */
                while (*str) {
                        unsigned int adjust;

                        wb->history[wb->pos] = state;
                        pos = base_idx(base[state]) + (u8) *str++;
                        if (check[pos] == state)
                                state = next[pos];
                        else
                                state = def[state];
                        if (is_loop(wb, state, &adjust)) {
                                state = aa_dfa_match(dfa, state, str);
                                *count -= adjust;
                                goto out;
                        }
                        inc_wb_pos(wb);
                        (*count)++;
                }
        }

out:
        if (!state)
                *count = 0;
        return state;
}

/**
 * aa_dfa_leftmatch - 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)
 * @count: current count of longest left.
 *
 * 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_leftmatch(struct aa_dfa *dfa, unsigned int start,
                              const char *str, unsigned int *count)
{
        DEFINE_MATCH_WB(wb);

        /* TODO: match for extended state dfas */

        return leftmatch_fb(dfa, start, str, &wb, count);
}