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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
c952780c | 5 | CRYPTO_EX_new, CRYPTO_EX_free, CRYPTO_EX_dup, |
e6390aca | 6 | CRYPTO_free_ex_index, CRYPTO_get_ex_new_index, CRYPTO_set_ex_data, |
c952780c | 7 | CRYPTO_get_ex_data, CRYPTO_free_ex_data, CRYPTO_new_ex_data |
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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, | |
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16 | CRYPTO_EX_new *new_func, |
17 | CRYPTO_EX_dup *dup_func, | |
18 | CRYPTO_EX_free *free_func); | |
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19 | |
20 | typedef int 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); | |
3c853776 | 24 | typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from, |
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25 | void *from_d, int idx, long argl, void *argp); |
26 | ||
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27 | int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad) |
28 | ||
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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 | ||
39 | Several OpenSSL structures can have application-specific data attached to them, | |
40 | known as "exdata." | |
41 | The specific structures are: | |
42 | ||
43 | SSL | |
44 | SSL_CTX | |
45 | SSL_SESSION | |
46 | X509 | |
47 | X509_STORE | |
48 | X509_STORE_CTX | |
49 | DH | |
50 | DSA | |
3aef36ff | 51 | EC_KEY |
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52 | RSA |
53 | ENGINE | |
54 | UI | |
18cfc668 | 55 | UI_METHOD |
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56 | BIO |
57 | ||
58 | Each is identified by an B<CRYPTO_EX_INDEX_xxx> define in the B<crypto.h> | |
59 | header file. In addition, B<CRYPTO_EX_INDEX_APP> is reserved for | |
60 | applications to use this facility for their own structures. | |
61 | ||
62 | The API described here is used by OpenSSL to manipulate exdata for specific | |
63 | structures. Since the application data can be anything at all it is passed | |
64 | and retrieved as a B<void *> type. | |
65 | ||
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66 | The B<CRYPTO_EX_DATA> type is opaque. To initialize the exdata part of |
67 | a structure, call CRYPTO_new_ex_data(). This is only necessary for | |
68 | B<CRYPTO_EX_INDEX_APP> objects. | |
69 | ||
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70 | Exdata types are identified by an B<index>, an integer guaranteed to be |
71 | unique within structures for the lifetime of the program. Applications | |
72 | using exdata typically call B<CRYPTO_get_ex_new_index> at startup, and | |
73 | store the result in a global variable, or write a wrapper function to | |
74 | provide lazy evaluation. The B<class_index> should be one of the | |
75 | B<CRYPTO_EX_INDEX_xxx> values. The B<argl> and B<argp> parameters are saved | |
76 | to be passed to the callbacks but are otherwise not used. In order to | |
77 | transparently manipulate exdata, three callbacks must be provided. The | |
78 | semantics of those callbacks are described below. | |
79 | ||
80 | When copying or releasing objects with exdata, the callback functions | |
81 | are called in increasing order of their B<index> value. | |
82 | ||
83 | If a dynamic library can be unloaded, it should call CRYPTO_free_ex_index() | |
84 | when this is done. | |
85 | This will replace the callbacks with no-ops | |
86 | so that applications don't crash. Any existing exdata will be leaked. | |
87 | ||
88 | To set or get the exdata on an object, the appropriate type-specific | |
89 | routine must be used. This is because the containing structure is opaque | |
90 | and the B<CRYPTO_EX_DATA> field is not accessible. In both API's, the | |
91 | B<idx> parameter should be an already-created index value. | |
92 | ||
93 | When setting exdata, the pointer specified with a particular index is saved, | |
94 | and returned on a subsequent "get" call. If the application is going to | |
95 | release the data, it must make sure to set a B<NULL> value at the index, | |
d3054fb6 | 96 | to avoid likely double-free crashes. |
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97 | |
98 | The function B<CRYPTO_free_ex_data> is used to free all exdata attached | |
99 | to a structure. The appropriate type-specific routine must be used. | |
100 | The B<class_index> identifies the structure type, the B<obj> is | |
101 | be the pointer to the actual structure, and B<r> is a pointer to the | |
102 | structure's exdata field. | |
103 | ||
104 | =head2 Callback Functions | |
105 | ||
106 | This section describes how the callback functions are used. Applications | |
107 | that are defining their own exdata using B<CYPRTO_EX_INDEX_APP> must | |
108 | call them as described here. | |
109 | ||
110 | When a structure is initially allocated (such as RSA_new()) then the | |
111 | new_func() is called for every defined index. There is no requirement | |
112 | that the entire parent, or containing, structure has been set up. | |
113 | The new_func() is typically used only to allocate memory to store the | |
114 | exdata, and perhaps an "initialized" flag within that memory. | |
115 | The exdata value should be set by calling CRYPTO_set_ex_data(). | |
116 | ||
117 | When a structure is free'd (such as SSL_CTX_free()) then the | |
118 | free_func() is called for every defined index. Again, the state of the | |
119 | parent structure is not guaranteed. The free_func() may be called with a | |
120 | NULL pointer. | |
121 | ||
122 | Both new_func() and free_func() take the same parameters. | |
123 | The B<parent> is the pointer to the structure that contains the exdata. | |
124 | The B<ptr> is the current exdata item; for new_func() this will typically | |
125 | be NULL. The B<r> parameter is a pointer to the exdata field of the object. | |
126 | The B<idx> is the index and is the value returned when the callbacks were | |
127 | initially registered via CRYPTO_get_ex_new_index() and can be used if | |
128 | the same callback handles different types of exdata. | |
129 | ||
130 | dup_func() is called when a structure is being copied. This is only done | |
131 | for B<SSL> and B<SSL_SESSION> objects. The B<to> and B<from> parameters | |
132 | are pointers to the destination and source B<CRYPTO_EX_DATA> structures, | |
133 | respectively. The B<srcp> parameter is a pointer to the source exdata. | |
134 | When the dup_func() returns, the value in B<srcp> is copied to the | |
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135 | destination ex_data. If the pointer contained in B<srcp> is not modified |
136 | by the dup_func(), then both B<to> and B<from> will point to the same data. | |
137 | The B<idx>, B<argl> and B<argp> parameters are as described for the other | |
138 | two callbacks. | |
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139 | |
140 | =head1 RETURN VALUES | |
141 | ||
142 | CRYPTO_get_ex_new_index() returns a new index or -1 on failure; the | |
143 | value B<0> is reserved for the legacy "app_data" API's. | |
144 | ||
145 | CRYPTO_free_ex_index() and | |
146 | CRYPTO_set_ex_data() return 1 on success or 0 on failure. | |
147 | ||
148 | CRYPTO_get_ex_data() returns the application data or NULL on failure; | |
149 | note that NULL may be a valid value. | |
150 | ||
151 | dup_func() should return 0 for failure and 1 for success. | |
152 | ||
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153 | =head1 COPYRIGHT |
154 | ||
9e183d22 | 155 | Copyright 2015-2017 The OpenSSL Project Authors. All Rights Reserved. |
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156 | |
157 | Licensed under the OpenSSL license (the "License"). You may not use | |
158 | this file except in compliance with the License. You can obtain a copy | |
159 | in the file LICENSE in the source distribution or at | |
160 | L<https://www.openssl.org/source/license.html>. | |
161 | ||
162 | =cut |