/* $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--;
        }
}