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
#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);
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.
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.
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.
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 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>.