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CRYPTO_get_ex_new_index(3) OpenSSL CRYPTO_get_ex_new_index(3)
NAME
CRYPTO_EX_new, CRYPTO_EX_free, CRYPTO_EX_dup, CRYPTO_free_ex_index,
CRYPTO_get_ex_new_index, CRYPTO_alloc_ex_data, CRYPTO_set_ex_data,
CRYPTO_get_ex_data, CRYPTO_free_ex_data, CRYPTO_new_ex_data - functions
supporting application-specific data
LIBRARY
libcrypto, -lcrypto
SYNOPSIS
#include <openssl/crypto.h>
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);
typedef void CRYPTO_EX_new(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
int idx, long argl, void *argp);
typedef void CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
int idx, long argl, void *argp);
typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
void **from_d, int idx, long argl, void *argp);
int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad);
int CRYPTO_alloc_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad,
int idx);
int CRYPTO_set_ex_data(CRYPTO_EX_DATA *r, int idx, void *arg);
void *CRYPTO_get_ex_data(const CRYPTO_EX_DATA *r, int idx);
void CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *r);
int CRYPTO_free_ex_index(int class_index, int idx);
DESCRIPTION
Several OpenSSL structures can have application-specific data attached
to them, known as "exdata." The specific structures are:
BIO
DH
DSA
EC_KEY
ENGINE
EVP_PKEY
RSA
SSL
SSL_CTX
SSL_SESSION
UI
UI_METHOD
X509
X509_STORE
X509_STORE_CTX
In addition, the APP name is reserved for use by application code.
Each is identified by an CRYPTO_EX_INDEX_xxx define in the header file
<openssl/crypto.h>. In addition, CRYPTO_EX_INDEX_APP is reserved for
applications to use this facility for their own structures.
The API described here is used by OpenSSL to manipulate exdata for
specific structures. Since the application data can be anything at all
it is passed and retrieved as a void * type.
The CRYPTO_EX_DATA type is opaque. To initialize the exdata part of a
structure, call CRYPTO_new_ex_data(). This is only necessary for
CRYPTO_EX_INDEX_APP objects.
Exdata types are identified by an index, an integer guaranteed to be
unique within structures for the lifetime of the program. Applications
using exdata typically call CRYPTO_get_ex_new_index at startup, and
store the result in a global variable, or write a wrapper function to
provide lazy evaluation. The class_index should be one of the
CRYPTO_EX_INDEX_xxx values. The argl and argp parameters are saved to
be passed to the callbacks but are otherwise not used. In order to
transparently manipulate exdata, three callbacks must be provided. The
semantics of those callbacks are described below.
When copying or releasing objects with exdata, the callback functions
are called in increasing order of their index value.
If a dynamic library can be unloaded, it should call
CRYPTO_free_ex_index() when this is done. This will replace the
callbacks with no-ops so that applications don't crash. Any existing
exdata will be leaked.
To set or get the exdata on an object, the appropriate type-specific
routine must be used. This is because the containing structure is
opaque and the CRYPTO_EX_DATA field is not accessible. In both API's,
the idx parameter should be an already-created index value.
When setting exdata, the pointer specified with a particular index is
saved, and returned on a subsequent "get" call. If the application is
going to release the data, it must make sure to set a NULL value at the
index, to avoid likely double-free crashes.
The function CRYPTO_free_ex_data is used to free all exdata attached to
a structure. The appropriate type-specific routine must be used. The
class_index identifies the structure type, the obj is a pointer to the
actual structure, and r is a pointer to the structure's exdata field.
Callback Functions
This section describes how the callback functions are used.
Applications that are defining their own exdata using
CYPRTO_EX_INDEX_APP must call them as described here.
When a structure is initially allocated (such as RSA_new()) then the
new_func() is called for every defined index. There is no requirement
that the entire parent, or containing, structure has been set up. The
new_func() is typically used only to allocate memory to store the
exdata, and perhaps an "initialized" flag within that memory. The
exdata value may be allocated later on with CRYPTO_alloc_ex_data(), or
may be set by calling CRYPTO_set_ex_data().
When a structure is free'd (such as SSL_CTX_free()) then the
free_func() is called for every defined index. Again, the state of the
parent structure is not guaranteed. The free_func() may be called with
a NULL pointer.
Both new_func() and free_func() take the same parameters. The parent
is the pointer to the structure that contains the exdata. The ptr is
the current exdata item; for new_func() this will typically be NULL.
The r parameter is a pointer to the exdata field of the object. The
idx is the index and is the value returned when the callbacks were
initially registered via CRYPTO_get_ex_new_index() and can be used if
the same callback handles different types of exdata.
dup_func() is called when a structure is being copied. This is only
done for SSL, SSL_SESSION, EC_KEY objects and BIO chains via
BIO_dup_chain(). The to and from parameters are pointers to the
destination and source CRYPTO_EX_DATA structures, respectively. The
*from_d parameter is a pointer to the source exdata. When the
dup_func() returns, the value in *from_d is copied to the destination
ex_data. If the pointer contained in *pptr is not modified by the
dup_func(), then both to and from will point to the same data. The
idx, argl and argp parameters are as described for the other two
callbacks. If the dup_func() returns 0 the whole CRYPTO_dup_ex_data()
will fail.
RETURN VALUES
CRYPTO_get_ex_new_index() returns a new index or -1 on failure.
CRYPTO_free_ex_index(), CRYPTO_alloc_ex_data() and CRYPTO_set_ex_data()
return 1 on success or 0 on failure.
CRYPTO_get_ex_data() returns the application data or NULL on failure;
note that NULL may be a valid value.
dup_func() should return 0 for failure and 1 for success.
HISTORY
CRYPTO_alloc_ex_data() was added in OpenSSL 3.0.
The signature of the dup_func() callback was changed in OpenSSL 3.0 to
use the type void ** for from_d. Previously this parameter was of type
void *.
Support for ENGINE "exdata" was deprecated in OpenSSL 3.0.
COPYRIGHT
Copyright 2015-2021 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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>.
3.0.12 2023-05-07 CRYPTO_get_ex_new_index(3)