/*

 * Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the OpenSSL license (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

#include "internal/cryptlib.h"

#include "bn_local.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 *);

static BIGNUM *BN_POOL_get(BN_POOL *, int);

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 *);

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;

    /* Flags. */

    int flags;

};

/* 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, "(%16p): ", 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

BN_CTX *BN_CTX_new(void)

{

    BN_CTX *ret;

    if ((ret = OPENSSL_zalloc(sizeof(*ret))) == NULL) {

        BNerr(BN_F_BN_CTX_NEW, ERR_R_MALLOC_FAILURE);

        return NULL;

    }

    /* Initialise the structure */

    BN_POOL_init(&ret->pool);

    BN_STACK_init(&ret->stack);

    return ret;

}

BN_CTX *BN_CTX_secure_new(void)

{

    BN_CTX *ret = BN_CTX_new();

    if (ret != NULL)

        ret->flags = BN_FLG_SECURE;

    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);

    OPENSSL_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)) {

        BNerr(BN_F_BN_CTX_START, 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, ctx->flags)) == NULL) {

        /*

         * Setting too_many prevents repeated "get" attempts from cluttering

         * the error stack.

         */

        ctx->too_many = 1;

        BNerr(BN_F_BN_CTX_GET, BN_R_TOO_MANY_TEMPORARY_VARIABLES);

        return NULL;

    }

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

    BN_zero(ret);

    /* clear BN_FLG_CONSTTIME if leaked from previous frames */

    ret->flags &= (~BN_FLG_CONSTTIME);

    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)

{

    OPENSSL_free(st->indexes);

    st->indexes = NULL;

}

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;

        if ((newitems = OPENSSL_malloc(sizeof(*newitems) * newsize)) == NULL) {

            BNerr(BN_F_BN_STACK_PUSH, ERR_R_MALLOC_FAILURE);

            return 0;

        }

        if (st->depth)

            memcpy(newitems, st->indexes, sizeof(*newitems) * st->depth);

        OPENSSL_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)

{

    unsigned int loop;

    BIGNUM *bn;

    while (p->head) {

        for (loop = 0, bn = p->head->vals; loop++ < BN_CTX_POOL_SIZE; bn++)

            if (bn->d)

                BN_clear_free(bn);

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

        OPENSSL_free(p->head);

        p->head = p->current;

    }

}

static BIGNUM *BN_POOL_get(BN_POOL *p, int flag)

{

    BIGNUM *bn;

    unsigned int loop;

    /* Full; allocate a new pool item and link it in. */

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

        BN_POOL_ITEM *item;

        if ((item = OPENSSL_malloc(sizeof(*item))) == NULL) {

            BNerr(BN_F_BN_POOL_GET, ERR_R_MALLOC_FAILURE);

            return NULL;

        }

        for (loop = 0, bn = item->vals; loop++ < BN_CTX_POOL_SIZE; bn++) {

            bn_init(bn);

            if ((flag & BN_FLG_SECURE) != 0)

                BN_set_flags(bn, BN_FLG_SECURE);

        }

        item->prev = p->tail;

        item->next = NULL;

        if (p->head == NULL)

            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 == 0) {

            offset = BN_CTX_POOL_SIZE - 1;

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

        } else

            offset--;

    }

}