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, CRYPTO_set_ex_data, 7CRYPTO_get_ex_data, CRYPTO_free_ex_data, CRYPTO_new_ex_data 8- functions supporting application-specific data 9 10=head1 SYNOPSIS 11 12 #include <openssl/crypto.h> 13 14 int CRYPTO_get_ex_new_index(int class_index, 15 long argl, void *argp, 16 CRYPTO_EX_new *new_func, 17 CRYPTO_EX_dup *dup_func, 18 CRYPTO_EX_free *free_func); 19 20 typedef void CRYPTO_EX_new(void *parent, void *ptr, CRYPTO_EX_DATA *ad, 21 int idx, long argl, void *argp); 22 typedef void CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad, 23 int idx, long argl, void *argp); 24 typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from, 25 void *from_d, int idx, long argl, void *argp); 26 27 int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad) 28 29 int CRYPTO_set_ex_data(CRYPTO_EX_DATA *r, int idx, void *arg); 30 31 void *CRYPTO_get_ex_data(CRYPTO_EX_DATA *r, int idx); 32 33 void CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *r); 34 35 int CRYPTO_free_ex_index(int class_index, int idx); 36 37=head1 DESCRIPTION 38 39Several OpenSSL structures can have application-specific data attached to them, 40known as "exdata." 41The specific structures are: 42 43 APP 44 BIO 45 DH 46 DRBG 47 DSA 48 EC_KEY 49 ENGINE 50 RSA 51 SSL 52 SSL_CTX 53 SSL_SESSION 54 UI 55 UI_METHOD 56 X509 57 X509_STORE 58 X509_STORE_CTX 59 60Each is identified by an B<CRYPTO_EX_INDEX_xxx> define in the B<crypto.h> 61header file. In addition, B<CRYPTO_EX_INDEX_APP> is reserved for 62applications to use this facility for their own structures. 63 64The API described here is used by OpenSSL to manipulate exdata for specific 65structures. Since the application data can be anything at all it is passed 66and retrieved as a B<void *> type. 67 68The B<CRYPTO_EX_DATA> type is opaque. To initialize the exdata part of 69a structure, call CRYPTO_new_ex_data(). This is only necessary for 70B<CRYPTO_EX_INDEX_APP> objects. 71 72Exdata types are identified by an B<index>, an integer guaranteed to be 73unique within structures for the lifetime of the program. Applications 74using exdata typically call B<CRYPTO_get_ex_new_index> at startup, and 75store the result in a global variable, or write a wrapper function to 76provide lazy evaluation. The B<class_index> should be one of the 77B<CRYPTO_EX_INDEX_xxx> values. The B<argl> and B<argp> parameters are saved 78to be passed to the callbacks but are otherwise not used. In order to 79transparently manipulate exdata, three callbacks must be provided. The 80semantics of those callbacks are described below. 81 82When copying or releasing objects with exdata, the callback functions 83are called in increasing order of their B<index> value. 84 85If a dynamic library can be unloaded, it should call CRYPTO_free_ex_index() 86when this is done. 87This will replace the callbacks with no-ops 88so that applications don't crash. Any existing exdata will be leaked. 89 90To set or get the exdata on an object, the appropriate type-specific 91routine must be used. This is because the containing structure is opaque 92and the B<CRYPTO_EX_DATA> field is not accessible. In both API's, the 93B<idx> parameter should be an already-created index value. 94 95When setting exdata, the pointer specified with a particular index is saved, 96and returned on a subsequent "get" call. If the application is going to 97release the data, it must make sure to set a B<NULL> value at the index, 98to avoid likely double-free crashes. 99 100The function B<CRYPTO_free_ex_data> is used to free all exdata attached 101to a structure. The appropriate type-specific routine must be used. 102The B<class_index> identifies the structure type, the B<obj> is 103a pointer to the actual structure, and B<r> is a pointer to the 104structure's exdata field. 105 106=head2 Callback Functions 107 108This section describes how the callback functions are used. Applications 109that are defining their own exdata using B<CYPRTO_EX_INDEX_APP> must 110call them as described here. 111 112When a structure is initially allocated (such as RSA_new()) then the 113new_func() is called for every defined index. There is no requirement 114that the entire parent, or containing, structure has been set up. 115The new_func() is typically used only to allocate memory to store the 116exdata, and perhaps an "initialized" flag within that memory. 117The exdata value should be set by calling CRYPTO_set_ex_data(). 118 119When a structure is free'd (such as SSL_CTX_free()) then the 120free_func() is called for every defined index. Again, the state of the 121parent structure is not guaranteed. The free_func() may be called with a 122NULL pointer. 123 124Both new_func() and free_func() take the same parameters. 125The B<parent> is the pointer to the structure that contains the exdata. 126The B<ptr> is the current exdata item; for new_func() this will typically 127be NULL. The B<r> parameter is a pointer to the exdata field of the object. 128The B<idx> is the index and is the value returned when the callbacks were 129initially registered via CRYPTO_get_ex_new_index() and can be used if 130the same callback handles different types of exdata. 131 132dup_func() is called when a structure is being copied. This is only done 133for B<SSL>, B<SSL_SESSION>, B<EC_KEY> objects and B<BIO> chains via 134BIO_dup_chain(). The B<to> and B<from> parameters 135are pointers to the destination and source B<CRYPTO_EX_DATA> structures, 136respectively. The B<from_d> parameter needs to be cast to a B<void **pptr> 137as the API has currently the wrong signature; that will be changed in a 138future version. The B<*pptr> is a pointer to the source exdata. 139When the dup_func() returns, the value in B<*pptr> is copied to the 140destination ex_data. If the pointer contained in B<*pptr> is not modified 141by the dup_func(), then both B<to> and B<from> will point to the same data. 142The B<idx>, B<argl> and B<argp> parameters are as described for the other 143two callbacks. If the dup_func() returns B<0> the whole CRYPTO_dup_ex_data() 144will fail. 145 146=head1 RETURN VALUES 147 148CRYPTO_get_ex_new_index() returns a new index or -1 on failure. 149 150CRYPTO_free_ex_index() and 151CRYPTO_set_ex_data() return 1 on success or 0 on failure. 152 153CRYPTO_get_ex_data() returns the application data or NULL on failure; 154note that NULL may be a valid value. 155 156dup_func() should return 0 for failure and 1 for success. 157 158=head1 COPYRIGHT 159 160Copyright 2015-2019 The OpenSSL Project Authors. All Rights Reserved. 161 162Licensed under the OpenSSL license (the "License"). You may not use 163this file except in compliance with the License. You can obtain a copy 164in the file LICENSE in the source distribution or at 165L<https://www.openssl.org/source/license.html>. 166 167=cut 168