openssl/crypto/ex_data.c

/* crypto/ex_data.c */

/*
 * Overhaul notes;
 *
 * This code is now *mostly* thread-safe. It is now easier to understand in what
 * ways it is safe and in what ways it is not, which is an improvement. Firstly,
 * all per-class stacks and index-counters for ex_data are stored in the same
 * global LHASH table (keyed by class). This hash table uses locking for all
 * access with the exception of CRYPTO_cleanup_all_ex_data(), which must only be
 * called when no other threads can possibly race against it (even if it was
 * locked, the race would mean it's possible the hash table might have been
 * recreated after the cleanup). As classes can only be added to the hash table,
 * and within each class, the stack of methods can only be incremented, the
 * locking mechanics are simpler than they would otherwise be. For example, the
 * new/dup/free ex_data functions will lock the hash table, copy the method
 * pointers it needs from the relevant class, then unlock the hash table before
 * actually applying those method pointers to the task of the new/dup/free
 * operations. As they can't be removed from the method-stack, only
 * supplemented, there's no race conditions associated with using them outside
 * the lock. The get/set_ex_data functions are not locked because they do not
 * involve this global state at all - they operate directly with a previously
 * obtained per-class method index and a particular "ex_data" variable. These
 * variables are usually instantiated per-context (eg. each RSA structure has
 * one) so locking on read/write access to that variable can be locked locally
 * if required (eg. using the "RSA" lock to synchronise access to a
 * per-RSA-structure ex_data variable if required).
 * [Geoff]
 */

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * 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 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 acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS 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 AUTHOR OR 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.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */
/* ====================================================================
 * Copyright (c) 1998-2001 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).
 *
 */

#include "cryptlib.h"
#include <openssl/lhash.h>

/* What an "implementation of ex_data functionality" looks like */
struct st_CRYPTO_EX_DATA_IMPL
	{
	/*********************/
	/* GLOBAL OPERATIONS */
	/* Return a new class index */
	int (*cb_new_class)(void);
	/* Cleanup all state used by the implementation */
	void (*cb_cleanup)(void);
	/************************/
	/* PER-CLASS OPERATIONS */
	/* Get a new method index within a class */
	int (*cb_get_new_index)(int class_index, long argl, void *argp,
			CRYPTO_EX_new *new_func, CRYPTO_EX_dup *dup_func,
			CRYPTO_EX_free *free_func);
	/* Initialise a new CRYPTO_EX_DATA of a given class */
	int (*cb_new_ex_data)(int class_index, void *obj,
			CRYPTO_EX_DATA *ad);
	/* Duplicate a CRYPTO_EX_DATA of a given class onto a copy */
	int (*cb_dup_ex_data)(int class_index, CRYPTO_EX_DATA *to,
			CRYPTO_EX_DATA *from);
	/* Cleanup a CRYPTO_EX_DATA of a given class */
	void (*cb_free_ex_data)(int class_index, void *obj,
			CRYPTO_EX_DATA *ad);
	};

/* The implementation we use at run-time */
static const CRYPTO_EX_DATA_IMPL *impl = NULL;

/* To call "impl" functions, use this macro rather than referring to 'impl' directly, eg.
 * EX_IMPL(get_new_index)(...); */
#define EX_IMPL(a) impl->cb_##a

/* Predeclare the "default" ex_data implementation */
static int int_new_class(void);
static void int_cleanup(void);
static int int_get_new_index(int class_index, long argl, void *argp,
		CRYPTO_EX_new *new_func, CRYPTO_EX_dup *dup_func,
		CRYPTO_EX_free *free_func);
static int int_new_ex_data(int class_index, void *obj,
		CRYPTO_EX_DATA *ad);
static int int_dup_ex_data(int class_index, CRYPTO_EX_DATA *to,
		CRYPTO_EX_DATA *from);
static void int_free_ex_data(int class_index, void *obj,
		CRYPTO_EX_DATA *ad);
static CRYPTO_EX_DATA_IMPL impl_default =
	{
	int_new_class,
	int_cleanup,
	int_get_new_index,
	int_new_ex_data,
	int_dup_ex_data,
	int_free_ex_data
	};

/* Internal function that checks whether "impl" is set and if not, sets it to
 * the default. */
static void impl_check(void)
	{
	CRYPTO_w_lock(CRYPTO_LOCK_EX_DATA);
	if(!impl)
		impl = &impl_default;
	CRYPTO_w_unlock(CRYPTO_LOCK_EX_DATA);
	}
/* A macro wrapper for impl_check that first uses a non-locked test before
 * invoking the function (which checks again inside a lock). */
#define IMPL_CHECK if(!impl) impl_check();

/* API functions to get/set the "ex_data" implementation */
const CRYPTO_EX_DATA_IMPL *CRYPTO_get_ex_data_implementation(void)
	{
	IMPL_CHECK
	return impl;
	}
int CRYPTO_set_ex_data_implementation(const CRYPTO_EX_DATA_IMPL *i)
	{
	int toret = 0;
	CRYPTO_w_lock(CRYPTO_LOCK_EX_DATA);
	if(!impl)
		{
		impl = i;
		toret = 1;
		}
	CRYPTO_w_unlock(CRYPTO_LOCK_EX_DATA);
	return toret;
	}

/****************************************************************************/
/* Interal (default) implementation of "ex_data" support. API functions are
 * further down. */

/* The type that represents what each "class" used to implement locally. A STACK
 * of CRYPTO_EX_DATA_FUNCS plus a index-counter. The 'class_index' is the global
 * value representing the class that is used to distinguish these items. */
typedef struct st_ex_class_item {
	int class_index;
	STACK_OF(CRYPTO_EX_DATA_FUNCS) *meth;
	int meth_num;
} EX_CLASS_ITEM;

/* When assigning new class indexes, this is our counter */
static int ex_class = CRYPTO_EX_INDEX_USER;

/* The global hash table of EX_CLASS_ITEM items */
static LHASH *ex_data = NULL;

/* The callbacks required in the "ex_data" hash table */
static unsigned long ex_hash_cb(const void *a_void)
	{
	return ((const EX_CLASS_ITEM *)a_void)->class_index;
	}
static int ex_cmp_cb(const void *a_void, const void *b_void)
	{
	return (((const EX_CLASS_ITEM *)a_void)->class_index -
		((const EX_CLASS_ITEM *)b_void)->class_index);
	}

/* Internal functions used by the "impl_default" implementation to access the
 * state */

static int ex_data_check(void)
	{
	int toret = 1;
	CRYPTO_w_lock(CRYPTO_LOCK_EX_DATA);
	if(!ex_data && ((ex_data = lh_new(ex_hash_cb, ex_cmp_cb)) == NULL))
		toret = 0;
	CRYPTO_w_unlock(CRYPTO_LOCK_EX_DATA);
	return toret;
	}
/* This macros helps reduce the locking from repeated checks because the
 * ex_data_check() function checks ex_data again inside a lock. */
#define EX_DATA_CHECK(iffail) if(!ex_data && !ex_data_check()) {iffail}

/* This "inner" callback is used by the callback function that follows it */
static void def_cleanup_util_cb(CRYPTO_EX_DATA_FUNCS *funcs)
	{
	OPENSSL_free(funcs);
	}

/* This callback is used in lh_doall to destroy all EX_CLASS_ITEM values from
 * "ex_data" prior to the ex_data hash table being itself destroyed. Doesn't do
 * any locking. */
static void def_cleanup_cb(void *a_void)
	{
	EX_CLASS_ITEM *item = (EX_CLASS_ITEM *)a_void;
	sk_CRYPTO_EX_DATA_FUNCS_pop_free(item->meth, def_cleanup_util_cb);
	OPENSSL_free(item);
	}

/* Return the EX_CLASS_ITEM from the "ex_data" hash table that corresponds to a
 * given class. Handles locking. */
static EX_CLASS_ITEM *def_get_class(int class_index)
	{
	EX_CLASS_ITEM d, *p, *gen;
	EX_DATA_CHECK(return NULL;)
	d.class_index = class_index;
	CRYPTO_w_lock(CRYPTO_LOCK_EX_DATA);
	p = lh_retrieve(ex_data, &d);
	if(!p)
		{
		gen = OPENSSL_malloc(sizeof(EX_CLASS_ITEM));
		if(gen)
			{
			gen->class_index = class_index;
			gen->meth_num = 0;
			gen->meth = sk_CRYPTO_EX_DATA_FUNCS_new_null();
			if(!gen->meth)
				OPENSSL_free(gen);
			else
				{
				/* Because we're inside the ex_data lock, the
				 * return value from the insert will be NULL */
				lh_insert(ex_data, gen);
				p = gen;
				}
			}
		}
	CRYPTO_w_unlock(CRYPTO_LOCK_EX_DATA);
	if(!p)
		CRYPTOerr(CRYPTO_F_DEF_GET_CLASS,ERR_R_MALLOC_FAILURE);
	return p;
	}

/* Add a new method to the given EX_CLASS_ITEM and return the corresponding
 * index (or -1 for error). Handles locking. */
static int def_add_index(EX_CLASS_ITEM *item, long argl, void *argp,
		CRYPTO_EX_new *new_func, CRYPTO_EX_dup *dup_func,
		CRYPTO_EX_free *free_func)
	{
	int toret = -1;
	CRYPTO_EX_DATA_FUNCS *a = (CRYPTO_EX_DATA_FUNCS *)OPENSSL_malloc(
					sizeof(CRYPTO_EX_DATA_FUNCS));
	if(!a)
		{
		CRYPTOerr(CRYPTO_F_DEF_ADD_INDEX,ERR_R_MALLOC_FAILURE);
		return -1;
		}
	a->argl=argl;
	a->argp=argp;
	a->new_func=new_func;
	a->dup_func=dup_func;
	a->free_func=free_func;
	CRYPTO_w_lock(CRYPTO_LOCK_EX_DATA);
	while (sk_CRYPTO_EX_DATA_FUNCS_num(item->meth) <= item->meth_num)
		{
		if (!sk_CRYPTO_EX_DATA_FUNCS_push(item->meth, NULL))
			{
			CRYPTOerr(CRYPTO_F_DEF_ADD_INDEX,ERR_R_MALLOC_FAILURE);
			OPENSSL_free(a);
			goto err;
			}
		}
	toret = item->meth_num++;
	sk_CRYPTO_EX_DATA_FUNCS_set(item->meth, toret, a);
err:
	CRYPTO_w_unlock(CRYPTO_LOCK_EX_DATA);
	return toret;
	}

/**************************************************************/
/* The functions in the default CRYPTO_EX_DATA_IMPL structure */

static int int_new_class(void)
	{
	int toret;
	CRYPTO_w_lock(CRYPTO_LOCK_EX_DATA);
	toret = ex_class++;
	CRYPTO_w_unlock(CRYPTO_LOCK_EX_DATA);
	return toret;
	}

static void int_cleanup(void)
	{
	EX_DATA_CHECK(return;)
	lh_doall(ex_data, def_cleanup_cb);
	lh_free(ex_data);
	ex_data = NULL;
	impl = NULL;
	}

static int int_get_new_index(int class_index, long argl, void *argp,
		CRYPTO_EX_new *new_func, CRYPTO_EX_dup *dup_func,
		CRYPTO_EX_free *free_func)
	{
	EX_CLASS_ITEM *item = def_get_class(class_index);
	if(!item)
		return -1;
	return def_add_index(item, argl, argp, new_func, dup_func, free_func);
	}

/* Thread-safe by copying a class's array of "CRYPTO_EX_DATA_FUNCS" entries in
 * the lock, then using them outside the lock. NB: Thread-safety only applies to
 * the global "ex_data" state (ie. class definitions), not thread-safe on 'ad'
 * itself. */
static int int_new_ex_data(int class_index, void *obj,
		CRYPTO_EX_DATA *ad)
	{
	int mx,i;
	void *ptr;
	CRYPTO_EX_DATA_FUNCS **storage = NULL;
	EX_CLASS_ITEM *item = def_get_class(class_index);
	if(!item)
		/* error is already set */
		return 0;
	ad->sk = NULL;
	CRYPTO_r_lock(CRYPTO_LOCK_EX_DATA);
	mx = sk_CRYPTO_EX_DATA_FUNCS_num(item->meth);
	if(mx > 0)
		{
		storage = OPENSSL_malloc(mx * sizeof(CRYPTO_EX_DATA_FUNCS*));
		if(!storage)
			goto skip;
		for(i = 0; i < mx; i++)
			storage[i] = sk_CRYPTO_EX_DATA_FUNCS_value(item->meth,i);
		}
skip:
	CRYPTO_r_unlock(CRYPTO_LOCK_EX_DATA);
	if((mx > 0) && !storage)
		{
		CRYPTOerr(CRYPTO_F_INT_NEW_EX_DATA,ERR_R_MALLOC_FAILURE);
		return 0;
		}
	for(i = 0; i < mx; i++)
		{
		if(storage[i] && storage[i]->new_func)
			{
			ptr = CRYPTO_get_ex_data(ad, i);
			storage[i]->new_func(obj,ptr,ad,i,
				storage[i]->argl,storage[i]->argp);
			}
		}
	if(storage)
		OPENSSL_free(storage);
	return 1;
	}

/* Same thread-safety notes as for "int_new_ex_data" */
static int int_dup_ex_data(int class_index, CRYPTO_EX_DATA *to,
		CRYPTO_EX_DATA *from)
	{
	int mx, j, i;
	char *ptr;
	CRYPTO_EX_DATA_FUNCS **storage = NULL;
	EX_CLASS_ITEM *item;
	if(!from->sk)
		/* 'to' should be "blank" which *is* just like 'from' */
		return 1;
	if((item = def_get_class(class_index)) == NULL)
		return 0;
	CRYPTO_r_lock(CRYPTO_LOCK_EX_DATA);
	mx = sk_CRYPTO_EX_DATA_FUNCS_num(item->meth);
	j = sk_num(from->sk);
	if(j < mx)
		mx = j;
	if(mx > 0)
		{
		storage = OPENSSL_malloc(mx * sizeof(CRYPTO_EX_DATA_FUNCS*));
		if(!storage)
			goto skip;
		for(i = 0; i < mx; i++)
			storage[i] = sk_CRYPTO_EX_DATA_FUNCS_value(item->meth,i);
		}
skip:
	CRYPTO_r_unlock(CRYPTO_LOCK_EX_DATA);
	if((mx > 0) && !storage)
		{
		CRYPTOerr(CRYPTO_F_INT_DUP_EX_DATA,ERR_R_MALLOC_FAILURE);
		return 0;
		}
	for(i = 0; i < mx; i++)
		{
		ptr = CRYPTO_get_ex_data(from, i);
		if(storage[i] && storage[i]->dup_func)
			storage[i]->dup_func(to,from,&ptr,i,
				storage[i]->argl,storage[i]->argp);
		CRYPTO_set_ex_data(to,i,ptr);
		}
	if(storage)
		OPENSSL_free(storage);
	return 1;
	}

/* Same thread-safety notes as for "int_new_ex_data" */
static void int_free_ex_data(int class_index, void *obj,
		CRYPTO_EX_DATA *ad)
	{
	int mx,i;
	EX_CLASS_ITEM *item;
	void *ptr;
	CRYPTO_EX_DATA_FUNCS **storage = NULL;
	if((item = def_get_class(class_index)) == NULL)
		return;
	CRYPTO_r_lock(CRYPTO_LOCK_EX_DATA);
	mx = sk_CRYPTO_EX_DATA_FUNCS_num(item->meth);
	if(mx > 0)
		{
		storage = OPENSSL_malloc(mx * sizeof(CRYPTO_EX_DATA_FUNCS*));
		if(!storage)
			goto skip;
		for(i = 0; i < mx; i++)
			storage[i] = sk_CRYPTO_EX_DATA_FUNCS_value(item->meth,i);
		}
skip:
	CRYPTO_r_unlock(CRYPTO_LOCK_EX_DATA);
	if((mx > 0) && !storage)
		{
		CRYPTOerr(CRYPTO_F_INT_FREE_EX_DATA,ERR_R_MALLOC_FAILURE);
		return;
		}
	for(i = 0; i < mx; i++)
		{
		if(storage[i] && storage[i]->free_func)
			{
			ptr = CRYPTO_get_ex_data(ad,i);
			storage[i]->free_func(obj,ptr,ad,i,
				storage[i]->argl,storage[i]->argp);
			}
		}
	if(storage)
		OPENSSL_free(storage);
	if(ad->sk)
		{
		sk_free(ad->sk);
		ad->sk=NULL;
		}
	}

/********************************************************************/
/* API functions that defer all "state" operations to the "ex_data"
 * implementation we have set. */

/* Obtain an index for a new class (not the same as getting a new index within
 * an existing class - this is actually getting a new *class*) */
int CRYPTO_ex_data_new_class(void)
	{
	IMPL_CHECK
	return EX_IMPL(new_class)();
	}

/* Release all "ex_data" state to prevent memory leaks. This can't be made
 * thread-safe without overhauling a lot of stuff, and shouldn't really be
 * called under potential race-conditions anyway (it's for program shutdown
 * after all). */
void CRYPTO_cleanup_all_ex_data(void)
	{
	IMPL_CHECK
	EX_IMPL(cleanup)();
	}

/* Inside an existing class, get/register a new index. */
int CRYPTO_get_ex_new_index(int class_index, long argl, void *argp,
		CRYPTO_EX_new *new_func, CRYPTO_EX_dup *dup_func,
		CRYPTO_EX_free *free_func)
	{
	int ret = -1;

	IMPL_CHECK
	ret = EX_IMPL(get_new_index)(class_index,
			argl, argp, new_func, dup_func, free_func);
	return ret;
	}

/* Initialise a new CRYPTO_EX_DATA for use in a particular class - including
 * calling new() callbacks for each index in the class used by this variable */
int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad)
	{
	IMPL_CHECK
	return EX_IMPL(new_ex_data)(class_index, obj, ad);
	}

/* Duplicate a CRYPTO_EX_DATA variable - including calling dup() callbacks for
 * each index in the class used by this variable */
int CRYPTO_dup_ex_data(int class_index, CRYPTO_EX_DATA *to,
	     CRYPTO_EX_DATA *from)
	{
	IMPL_CHECK
	return EX_IMPL(dup_ex_data)(class_index, to, from);
	}

/* Cleanup a CRYPTO_EX_DATA variable - including calling free() callbacks for
 * each index in the class used by this variable */
void CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad)
	{
	IMPL_CHECK
	EX_IMPL(free_ex_data)(class_index, obj, ad);
	}

/* For a given CRYPTO_EX_DATA variable, set the value corresponding to a
 * particular index in the class used by this variable */
int CRYPTO_set_ex_data(CRYPTO_EX_DATA *ad, int idx, void *val)
	{
	int i;

	if (ad->sk == NULL)
		{
		if ((ad->sk=sk_new_null()) == NULL)
			{
			CRYPTOerr(CRYPTO_F_CRYPTO_SET_EX_DATA,ERR_R_MALLOC_FAILURE);
			return(0);
			}
		}
	i=sk_num(ad->sk);

	while (i <= idx)
		{
		if (!sk_push(ad->sk,NULL))
			{
			CRYPTOerr(CRYPTO_F_CRYPTO_SET_EX_DATA,ERR_R_MALLOC_FAILURE);
			return(0);
			}
		i++;
		}
	sk_set(ad->sk,idx,val);
	return(1);
	}

/* For a given CRYPTO_EX_DATA_ variable, get the value corresponding to a
 * particular index in the class used by this variable */
void *CRYPTO_get_ex_data(const CRYPTO_EX_DATA *ad, int idx)
	{
	if (ad->sk == NULL)
		return(0);
	else if (idx >= sk_num(ad->sk))
		return(0);
	else
		return(sk_value(ad->sk,idx));
	}

IMPLEMENT_STACK_OF(CRYPTO_EX_DATA_FUNCS)