/* $OpenBSD: bn_ctx.c,v 1.16 2019/08/20 10:59:09 schwarze Exp $ */

/* Written by Ulf Moeller for the OpenSSL project. */

/* ====================================================================

 * Copyright (c) 1998-2004 The OpenSSL Project.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 *

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in

 *    the documentation and/or other materials provided with the

 *    distribution.

 *

 * 3. All advertising materials mentioning features or use of this

 *    software must display the following acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"

 *

 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to

 *    endorse or promote products derived from this software without

 *    prior written permission. For written permission, please contact

 *    openssl-core@openssl.org.

 *

 * 5. Products derived from this software may not be called "OpenSSL"

 *    nor may "OpenSSL" appear in their names without prior written

 *    permission of the OpenSSL Project.

 *

 * 6. Redistributions of any form whatsoever must retain the following

 *    acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"

 *

 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY

 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR

 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,

 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED

 * OF THE POSSIBILITY OF SUCH DAMAGE.

 * ====================================================================

 *

 * This product includes cryptographic software written by Eric Young

 * (eay@cryptsoft.com).  This product includes software written by Tim

 * Hudson (tjh@cryptsoft.com).

 *

 */

#if !defined(BN_CTX_DEBUG) && !defined(BN_DEBUG)

#ifndef NDEBUG

#define NDEBUG

#endif

#endif

#include <stdio.h>

#include <string.h>

#include <openssl/opensslconf.h>

#include <openssl/err.h>

#include "bn_lcl.h"

/* TODO list

 *

 * 1. Check a bunch of "(words+1)" type hacks in various bignum functions and

 * check they can be safely removed.

 *  - Check +1 and other ugliness in BN_from_montgomery()

 *

 * 2. Consider allowing a BN_new_ex() that, at least, lets you specify an

 * appropriate 'block' size that will be honoured by bn_expand_internal() to

 * prevent piddly little reallocations. OTOH, profiling bignum expansions in

 * BN_CTX doesn't show this to be a big issue.

 */

/* How many bignums are in each "pool item"; */

#define BN_CTX_POOL_SIZE  16

/* The stack frame info is resizing, set a first-time expansion size; */

#define BN_CTX_START_FRAMES 32

/***********/

/* BN_POOL */

/***********/

/* A bundle of bignums that can be linked with other bundles */

typedef struct bignum_pool_item {

  /* The bignum values */

  BIGNUM vals[BN_CTX_POOL_SIZE];

  /* Linked-list admin */

  struct bignum_pool_item *prev, *next;

} BN_POOL_ITEM;

/* A linked-list of bignums grouped in bundles */

typedef struct bignum_pool {

  /* Linked-list admin */

  BN_POOL_ITEM *head, *current, *tail;

  /* Stack depth and allocation size */

  unsigned used, size;

} BN_POOL;

static void   BN_POOL_init(BN_POOL *);

static void   BN_POOL_finish(BN_POOL *);

#ifndef OPENSSL_NO_DEPRECATED

static void   BN_POOL_reset(BN_POOL *);

#endif

static BIGNUM *   BN_POOL_get(BN_POOL *);

static void   BN_POOL_release(BN_POOL *, unsigned int);

/************/

/* BN_STACK */

/************/

/* A wrapper to manage the "stack frames" */

typedef struct bignum_ctx_stack {

  /* Array of indexes into the bignum stack */

  unsigned int *indexes;

  /* Number of stack frames, and the size of the allocated array */

  unsigned int depth, size;

} BN_STACK;

static void   BN_STACK_init(BN_STACK *);

static void   BN_STACK_finish(BN_STACK *);

#ifndef OPENSSL_NO_DEPRECATED

static void   BN_STACK_reset(BN_STACK *);

#endif

static int    BN_STACK_push(BN_STACK *, unsigned int);

static unsigned int BN_STACK_pop(BN_STACK *);

/**********/

/* BN_CTX */

/**********/

/* The opaque BN_CTX type */

struct bignum_ctx {

  /* The bignum bundles */

  BN_POOL pool;

  /* The "stack frames", if you will */

  BN_STACK stack;

  /* The number of bignums currently assigned */

  unsigned int used;

  /* Depth of stack overflow */

  int err_stack;

  /* Block "gets" until an "end" (compatibility behaviour) */

  int too_many;

};

/* Enable this to find BN_CTX bugs */

#ifdef BN_CTX_DEBUG

static const char *ctxdbg_cur = NULL;

static void

ctxdbg(BN_CTX *ctx)

{

  unsigned int bnidx = 0, fpidx = 0;

  BN_POOL_ITEM *item = ctx->pool.head;

  BN_STACK *stack = &ctx->stack;

  fprintf(stderr, "(%08x): ", (unsigned int)ctx);

  while (bnidx < ctx->used) {

    fprintf(stderr, "%03x ",

        item->vals[bnidx++ % BN_CTX_POOL_SIZE].dmax);

    if (!(bnidx % BN_CTX_POOL_SIZE))

      item = item->next;

  }

  fprintf(stderr, "\n");

  bnidx = 0;

  fprintf(stderr, "          : ");

  while (fpidx < stack->depth) {

    while (bnidx++ < stack->indexes[fpidx])

      fprintf(stderr, "    ");

    fprintf(stderr, "^^^ ");

    bnidx++;

    fpidx++;

  }

  fprintf(stderr, "\n");

}

#define CTXDBG_ENTRY(str, ctx) \

  do { \

    ctxdbg_cur = (str); \

    fprintf(stderr, "Starting %s\n", ctxdbg_cur); \

    ctxdbg(ctx); \

  } while(0)

#define CTXDBG_EXIT(ctx) \

  do { \

    fprintf(stderr, "Ending %s\n", ctxdbg_cur); \

    ctxdbg(ctx); \

  } while(0)

#define CTXDBG_RET(ctx,ret)

#else

#define CTXDBG_ENTRY(str, ctx)

#define CTXDBG_EXIT(ctx)

#define CTXDBG_RET(ctx,ret)

#endif

/* This function is an evil legacy and should not be used. This implementation

 * is WYSIWYG, though I've done my best. */

#ifndef OPENSSL_NO_DEPRECATED

void

BN_CTX_init(BN_CTX *ctx)

{

  /* Assume the caller obtained the context via BN_CTX_new() and so is

   * trying to reset it for use. Nothing else makes sense, least of all

   * binary compatibility from a time when they could declare a static

   * variable. */

  BN_POOL_reset(&ctx->pool);

  BN_STACK_reset(&ctx->stack);

  ctx->used = 0;

  ctx->err_stack = 0;

  ctx->too_many = 0;

}

#endif

BN_CTX *

BN_CTX_new(void)

{

  BN_CTX *ret = malloc(sizeof(BN_CTX));

  if (!ret) {

    BNerror(ERR_R_MALLOC_FAILURE);

    return NULL;

  }

  /* Initialise the structure */

  BN_POOL_init(&ret->pool);

  BN_STACK_init(&ret->stack);

  ret->used = 0;

  ret->err_stack = 0;

  ret->too_many = 0;

  return ret;

}

void

BN_CTX_free(BN_CTX *ctx)

{

  if (ctx == NULL)

    return;

#ifdef BN_CTX_DEBUG

  {

    BN_POOL_ITEM *pool = ctx->pool.head;

    fprintf(stderr, "BN_CTX_free, stack-size=%d, pool-bignums=%d\n",

        ctx->stack.size, ctx->pool.size);

    fprintf(stderr, "dmaxs: ");

    while (pool) {

      unsigned loop = 0;

      while (loop < BN_CTX_POOL_SIZE)

        fprintf(stderr, "%02x ",

            pool->vals[loop++].dmax);

      pool = pool->next;

    }

    fprintf(stderr, "\n");

  }

#endif

  BN_STACK_finish(&ctx->stack);

  BN_POOL_finish(&ctx->pool);

  free(ctx);

}

void

BN_CTX_start(BN_CTX *ctx)

{

  CTXDBG_ENTRY("BN_CTX_start", ctx);

  /* If we're already overflowing ... */

  if (ctx->err_stack || ctx->too_many)

    ctx->err_stack++;

  /* (Try to) get a new frame pointer */

  else if (!BN_STACK_push(&ctx->stack, ctx->used)) {

    BNerror(BN_R_TOO_MANY_TEMPORARY_VARIABLES);

    ctx->err_stack++;

  }

  CTXDBG_EXIT(ctx);

}

void

BN_CTX_end(BN_CTX *ctx)

{

  if (ctx == NULL)

    return;

  CTXDBG_ENTRY("BN_CTX_end", ctx);

  if (ctx->err_stack)

    ctx->err_stack--;

  else {

    unsigned int fp = BN_STACK_pop(&ctx->stack);

    /* Does this stack frame have anything to release? */

    if (fp < ctx->used)

      BN_POOL_release(&ctx->pool, ctx->used - fp);

    ctx->used = fp;

    /* Unjam "too_many" in case "get" had failed */

    ctx->too_many = 0;

  }

  CTXDBG_EXIT(ctx);

}

BIGNUM *

BN_CTX_get(BN_CTX *ctx)

{

  BIGNUM *ret;

  CTXDBG_ENTRY("BN_CTX_get", ctx);

  if (ctx->err_stack || ctx->too_many)

    return NULL;

  if ((ret = BN_POOL_get(&ctx->pool)) == NULL) {

    /* Setting too_many prevents repeated "get" attempts from

     * cluttering the error stack. */

    ctx->too_many = 1;

    BNerror(BN_R_TOO_MANY_TEMPORARY_VARIABLES);

    return NULL;

  }

  /* OK, make sure the returned bignum is "zero" */

  BN_zero(ret);

  ctx->used++;

  CTXDBG_RET(ctx, ret);

  return ret;

}

/************/

/* BN_STACK */

/************/

static void

BN_STACK_init(BN_STACK *st)

{

  st->indexes = NULL;

  st->depth = st->size = 0;

}

static void

BN_STACK_finish(BN_STACK *st)

{

  if (st->size)

    free(st->indexes);

}

#ifndef OPENSSL_NO_DEPRECATED

static void

BN_STACK_reset(BN_STACK *st)

{

  st->depth = 0;

}

#endif

static int

BN_STACK_push(BN_STACK *st, unsigned int idx)

{

  if (st->depth == st->size)

    /* Need to expand */

  {

    unsigned int newsize = (st->size ?

        (st->size * 3 / 2) : BN_CTX_START_FRAMES);

    unsigned int *newitems = reallocarray(NULL,

        newsize, sizeof(unsigned int));

    if (!newitems)

      return 0;

    if (st->depth)

      memcpy(newitems, st->indexes, st->depth *

          sizeof(unsigned int));

    if (st->size)

      free(st->indexes);

    st->indexes = newitems;

    st->size = newsize;

  }

  st->indexes[(st->depth)++] = idx;

  return 1;

}

static unsigned int

BN_STACK_pop(BN_STACK *st)

{

  return st->indexes[--(st->depth)];

}

/***********/

/* BN_POOL */

/***********/

static void

BN_POOL_init(BN_POOL *p)

{

  p->head = p->current = p->tail = NULL;

  p->used = p->size = 0;

}

static void

BN_POOL_finish(BN_POOL *p)

{

  while (p->head) {

    unsigned int loop = 0;

    BIGNUM *bn = p->head->vals;

    while (loop++ < BN_CTX_POOL_SIZE) {

      if (bn->d)

        BN_clear_free(bn);

      bn++;

    }

    p->current = p->head->next;

    free(p->head);

    p->head = p->current;

  }

}

#ifndef OPENSSL_NO_DEPRECATED

static void

BN_POOL_reset(BN_POOL *p)

{

  BN_POOL_ITEM *item = p->head;

  while (item) {

    unsigned int loop = 0;

    BIGNUM *bn = item->vals;

    while (loop++ < BN_CTX_POOL_SIZE) {

      if (bn->d)

        BN_clear(bn);

      bn++;

    }

    item = item->next;

  }

  p->current = p->head;

  p->used = 0;

}

#endif

static BIGNUM *

BN_POOL_get(BN_POOL *p)

{

  if (p->used == p->size) {

    BIGNUM *bn;

    unsigned int loop = 0;

    BN_POOL_ITEM *item = malloc(sizeof(BN_POOL_ITEM));

    if (!item)

      return NULL;

    /* Initialise the structure */

    bn = item->vals;

    while (loop++ < BN_CTX_POOL_SIZE)

      BN_init(bn++);

    item->prev = p->tail;

    item->next = NULL;

    /* Link it in */

    if (!p->head)

      p->head = p->current = p->tail = item;

    else {

      p->tail->next = item;

      p->tail = item;

      p->current = item;

    }

    p->size += BN_CTX_POOL_SIZE;

    p->used++;

    /* Return the first bignum from the new pool */

    return item->vals;

  }

  if (!p->used)

    p->current = p->head;

  else if ((p->used % BN_CTX_POOL_SIZE) == 0)

    p->current = p->current->next;

  return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);

}

static void

BN_POOL_release(BN_POOL *p, unsigned int num)

{

  unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;

  p->used -= num;

  while (num--) {

    bn_check_top(p->current->vals + offset);

    if (!offset) {

      offset = BN_CTX_POOL_SIZE - 1;

      p->current = p->current->prev;

    } else

      offset--;

  }

}