1=pod 2 3=head1 NAME 4 5CRYPTO_EX_new, CRYPTO_EX_free, CRYPTO_EX_dup, 6CRYPTO_free_ex_index, CRYPTO_get_ex_new_index, 7CRYPTO_alloc_ex_data, CRYPTO_set_ex_data, CRYPTO_get_ex_data, 8CRYPTO_free_ex_data, CRYPTO_new_ex_data 9- functions supporting application-specific data 10 11=head1 SYNOPSIS 12 13 #include <openssl/crypto.h> 14 15 int CRYPTO_get_ex_new_index(int class_index, 16 long argl, void *argp, 17 CRYPTO_EX_new *new_func, 18 CRYPTO_EX_dup *dup_func, 19 CRYPTO_EX_free *free_func); 20 21 typedef void CRYPTO_EX_new(void *parent, void *ptr, CRYPTO_EX_DATA *ad, 22 int idx, long argl, void *argp); 23 typedef void CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad, 24 int idx, long argl, void *argp); 25 typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from, 26 void **from_d, int idx, long argl, void *argp); 27 28 int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad); 29 30 int CRYPTO_alloc_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad, 31 int idx); 32 33 int CRYPTO_set_ex_data(CRYPTO_EX_DATA *r, int idx, void *arg); 34 35 void *CRYPTO_get_ex_data(const CRYPTO_EX_DATA *r, int idx); 36 37 void CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *r); 38 39 int CRYPTO_free_ex_index(int class_index, int idx); 40 41=head1 DESCRIPTION 42 43Several OpenSSL structures can have application-specific data attached to them, 44known as "exdata." 45The specific structures are: 46 47 BIO 48 DH 49 DSA 50 EC_KEY 51 ENGINE 52 EVP_PKEY 53 RSA 54 SSL 55 SSL_CTX 56 SSL_SESSION 57 UI 58 UI_METHOD 59 X509 60 X509_STORE 61 X509_STORE_CTX 62 63In addition, the B<APP> name is reserved for use by application code. 64 65Each is identified by an B<CRYPTO_EX_INDEX_xxx> define in the header file 66F<< <openssl/crypto.h> >>. In addition, B<CRYPTO_EX_INDEX_APP> is reserved for 67applications to use this facility for their own structures. 68 69The API described here is used by OpenSSL to manipulate exdata for specific 70structures. Since the application data can be anything at all it is passed 71and retrieved as a B<void *> type. 72 73The B<CRYPTO_EX_DATA> type is opaque. To initialize the exdata part of 74a structure, call CRYPTO_new_ex_data(). This is only necessary for 75B<CRYPTO_EX_INDEX_APP> objects. 76 77Exdata types are identified by an B<index>, an integer guaranteed to be 78unique within structures for the lifetime of the program. Applications 79using exdata typically call B<CRYPTO_get_ex_new_index> at startup, and 80store the result in a global variable, or write a wrapper function to 81provide lazy evaluation. The B<class_index> should be one of the 82B<CRYPTO_EX_INDEX_xxx> values. The B<argl> and B<argp> parameters are saved 83to be passed to the callbacks but are otherwise not used. In order to 84transparently manipulate exdata, three callbacks must be provided. The 85semantics of those callbacks are described below. 86 87When copying or releasing objects with exdata, the callback functions 88are called in increasing order of their B<index> value. 89 90If a dynamic library can be unloaded, it should call CRYPTO_free_ex_index() 91when this is done. 92This will replace the callbacks with no-ops 93so that applications don't crash. Any existing exdata will be leaked. 94 95To set or get the exdata on an object, the appropriate type-specific 96routine must be used. This is because the containing structure is opaque 97and the B<CRYPTO_EX_DATA> field is not accessible. In both API's, the 98B<idx> parameter should be an already-created index value. 99 100When setting exdata, the pointer specified with a particular index is saved, 101and returned on a subsequent "get" call. If the application is going to 102release the data, it must make sure to set a B<NULL> value at the index, 103to avoid likely double-free crashes. 104 105The function B<CRYPTO_free_ex_data> is used to free all exdata attached 106to a structure. The appropriate type-specific routine must be used. 107The B<class_index> identifies the structure type, the B<obj> is 108a pointer to the actual structure, and B<r> is a pointer to the 109structure's exdata field. 110 111=head2 Callback Functions 112 113This section describes how the callback functions are used. Applications 114that are defining their own exdata using B<CYPRTO_EX_INDEX_APP> must 115call them as described here. 116 117When a structure is initially allocated (such as RSA_new()) then the 118new_func() is called for every defined index. There is no requirement 119that the entire parent, or containing, structure has been set up. 120The new_func() is typically used only to allocate memory to store the 121exdata, and perhaps an "initialized" flag within that memory. 122The exdata value may be allocated later on with CRYPTO_alloc_ex_data(), 123or may be set by calling CRYPTO_set_ex_data(). 124 125When a structure is free'd (such as SSL_CTX_free()) then the 126free_func() is called for every defined index. Again, the state of the 127parent structure is not guaranteed. The free_func() may be called with a 128NULL pointer. 129 130Both new_func() and free_func() take the same parameters. 131The B<parent> is the pointer to the structure that contains the exdata. 132The B<ptr> is the current exdata item; for new_func() this will typically 133be NULL. The B<r> parameter is a pointer to the exdata field of the object. 134The B<idx> is the index and is the value returned when the callbacks were 135initially registered via CRYPTO_get_ex_new_index() and can be used if 136the same callback handles different types of exdata. 137 138dup_func() is called when a structure is being copied. This is only done 139for B<SSL>, B<SSL_SESSION>, B<EC_KEY> objects and B<BIO> chains via 140BIO_dup_chain(). The B<to> and B<from> parameters 141are pointers to the destination and source B<CRYPTO_EX_DATA> structures, 142respectively. The B<*from_d> parameter is a pointer to the source exdata. 143When the dup_func() returns, the value in B<*from_d> is copied to the 144destination ex_data. If the pointer contained in B<*pptr> is not modified 145by the dup_func(), then both B<to> and B<from> will point to the same data. 146The B<idx>, B<argl> and B<argp> parameters are as described for the other 147two callbacks. If the dup_func() returns B<0> the whole CRYPTO_dup_ex_data() 148will fail. 149 150=head1 RETURN VALUES 151 152CRYPTO_get_ex_new_index() returns a new index or -1 on failure. 153 154CRYPTO_free_ex_index(), CRYPTO_alloc_ex_data() and CRYPTO_set_ex_data() 155return 1 on success or 0 on failure. 156 157CRYPTO_get_ex_data() returns the application data or NULL on failure; 158note that NULL may be a valid value. 159 160dup_func() should return 0 for failure and 1 for success. 161 162=head1 HISTORY 163 164CRYPTO_alloc_ex_data() was added in OpenSSL 3.0. 165 166The signature of the dup_func() callback was changed in OpenSSL 3.0 to use the 167type B<void **> for B<from_d>. Previously this parameter was of type B<void *>. 168 169Support for ENGINE "exdata" was deprecated in OpenSSL 3.0. 170 171=head1 COPYRIGHT 172 173Copyright 2015-2021 The OpenSSL Project Authors. All Rights Reserved. 174 175Licensed under the Apache License 2.0 (the "License"). You may not use 176this file except in compliance with the License. You can obtain a copy 177in the file LICENSE in the source distribution or at 178L<https://www.openssl.org/source/license.html>. 179 180=cut 181