302 lines
12 KiB
Groff
Executable File
302 lines
12 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "CRYPTO_GET_EX_NEW_INDEX 3"
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.TH CRYPTO_GET_EX_NEW_INDEX 3 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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CRYPTO_EX_new, CRYPTO_EX_free, CRYPTO_EX_dup,
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CRYPTO_free_ex_index, CRYPTO_get_ex_new_index,
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CRYPTO_alloc_ex_data, CRYPTO_set_ex_data, CRYPTO_get_ex_data,
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CRYPTO_free_ex_data, CRYPTO_new_ex_data
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\&\- functions supporting application\-specific data
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/crypto.h>
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\&
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\& int CRYPTO_get_ex_new_index(int class_index,
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\& long argl, void *argp,
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\& CRYPTO_EX_new *new_func,
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\& CRYPTO_EX_dup *dup_func,
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\& CRYPTO_EX_free *free_func);
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\&
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\& typedef void CRYPTO_EX_new(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
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\& int idx, long argl, void *argp);
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\& typedef void CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
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\& int idx, long argl, void *argp);
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\& typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
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\& void *from_d, int idx, long argl, void *argp);
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\&
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\& int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad)
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\&
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\& int CRYPTO_alloc_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad,
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\& int idx);
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\&
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\& int CRYPTO_set_ex_data(CRYPTO_EX_DATA *r, int idx, void *arg);
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\&
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\& void *CRYPTO_get_ex_data(CRYPTO_EX_DATA *r, int idx);
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\&
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\& void CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *r);
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\&
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\& int CRYPTO_free_ex_index(int class_index, int idx);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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Several OpenSSL structures can have application-specific data attached to them,
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known as \*(L"exdata.\*(R"
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The specific structures are:
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.PP
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.Vb 10
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\& BIO
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\& DH
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\& DSA
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\& EC_KEY
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\& ENGINE
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\& RAND_DRBG
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\& RSA
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\& SSL
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\& SSL_CTX
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\& SSL_SESSION
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\& UI
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\& UI_METHOD
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\& X509
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\& X509_STORE
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\& X509_STORE_CTX
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.Ve
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.PP
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In addition, the \fB\s-1APP\s0\fR name is reserved for use by application code.
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.PP
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Each is identified by an \fBCRYPTO_EX_INDEX_xxx\fR define in the \fBcrypto.h\fR
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header file. In addition, \fB\s-1CRYPTO_EX_INDEX_APP\s0\fR is reserved for
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applications to use this facility for their own structures.
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.PP
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The \s-1API\s0 described here is used by OpenSSL to manipulate exdata for specific
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structures. Since the application data can be anything at all it is passed
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and retrieved as a \fBvoid *\fR type.
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.PP
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The \fB\s-1CRYPTO_EX_DATA\s0\fR type is opaque. To initialize the exdata part of
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a structure, call \fICRYPTO_new_ex_data()\fR. This is only necessary for
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\&\fB\s-1CRYPTO_EX_INDEX_APP\s0\fR objects.
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.PP
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Exdata types are identified by an \fBindex\fR, an integer guaranteed to be
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unique within structures for the lifetime of the program. Applications
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using exdata typically call \fBCRYPTO_get_ex_new_index\fR at startup, and
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store the result in a global variable, or write a wrapper function to
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provide lazy evaluation. The \fBclass_index\fR should be one of the
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\&\fBCRYPTO_EX_INDEX_xxx\fR values. The \fBargl\fR and \fBargp\fR parameters are saved
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to be passed to the callbacks but are otherwise not used. In order to
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transparently manipulate exdata, three callbacks must be provided. The
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semantics of those callbacks are described below.
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.PP
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When copying or releasing objects with exdata, the callback functions
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are called in increasing order of their \fBindex\fR value.
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.PP
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If a dynamic library can be unloaded, it should call \fICRYPTO_free_ex_index()\fR
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when this is done.
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This will replace the callbacks with no-ops
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so that applications don't crash. Any existing exdata will be leaked.
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.PP
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To set or get the exdata on an object, the appropriate type-specific
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routine must be used. This is because the containing structure is opaque
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and the \fB\s-1CRYPTO_EX_DATA\s0\fR field is not accessible. In both \s-1API\s0's, the
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\&\fBidx\fR parameter should be an already-created index value.
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.PP
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When setting exdata, the pointer specified with a particular index is saved,
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and returned on a subsequent \*(L"get\*(R" call. If the application is going to
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release the data, it must make sure to set a \fB\s-1NULL\s0\fR value at the index,
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to avoid likely double-free crashes.
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.PP
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The function \fBCRYPTO_free_ex_data\fR is used to free all exdata attached
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to a structure. The appropriate type-specific routine must be used.
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The \fBclass_index\fR identifies the structure type, the \fBobj\fR is
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a pointer to the actual structure, and \fBr\fR is a pointer to the
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structure's exdata field.
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.SS "Callback Functions"
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.IX Subsection "Callback Functions"
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This section describes how the callback functions are used. Applications
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that are defining their own exdata using \fB\s-1CYPRTO_EX_INDEX_APP\s0\fR must
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call them as described here.
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.PP
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When a structure is initially allocated (such as \fIRSA_new()\fR) then the
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\&\fInew_func()\fR is called for every defined index. There is no requirement
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that the entire parent, or containing, structure has been set up.
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The \fInew_func()\fR is typically used only to allocate memory to store the
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exdata, and perhaps an \*(L"initialized\*(R" flag within that memory.
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The exdata value may be allocated later on with \fICRYPTO_alloc_ex_data()\fR,
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or may be set by calling \fICRYPTO_set_ex_data()\fR.
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.PP
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When a structure is free'd (such as \fISSL_CTX_free()\fR) then the
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\&\fIfree_func()\fR is called for every defined index. Again, the state of the
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parent structure is not guaranteed. The \fIfree_func()\fR may be called with a
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\&\s-1NULL\s0 pointer.
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.PP
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Both \fInew_func()\fR and \fIfree_func()\fR take the same parameters.
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The \fBparent\fR is the pointer to the structure that contains the exdata.
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The \fBptr\fR is the current exdata item; for \fInew_func()\fR this will typically
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be \s-1NULL\s0. The \fBr\fR parameter is a pointer to the exdata field of the object.
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The \fBidx\fR is the index and is the value returned when the callbacks were
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initially registered via \fICRYPTO_get_ex_new_index()\fR and can be used if
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the same callback handles different types of exdata.
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.PP
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\&\fIdup_func()\fR is called when a structure is being copied. This is only done
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for \fB\s-1SSL\s0\fR, \fB\s-1SSL_SESSION\s0\fR, \fB\s-1EC_KEY\s0\fR objects and \fB\s-1BIO\s0\fR chains via
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\&\fIBIO_dup_chain()\fR. The \fBto\fR and \fBfrom\fR parameters
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are pointers to the destination and source \fB\s-1CRYPTO_EX_DATA\s0\fR structures,
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respectively. The \fBfrom_d\fR parameter needs to be cast to a \fBvoid **pptr\fR
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as the \s-1API\s0 has currently the wrong signature; that will be changed in a
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future version. The \fB*pptr\fR is a pointer to the source exdata.
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When the \fIdup_func()\fR returns, the value in \fB*pptr\fR is copied to the
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destination ex_data. If the pointer contained in \fB*pptr\fR is not modified
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by the \fIdup_func()\fR, then both \fBto\fR and \fBfrom\fR will point to the same data.
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The \fBidx\fR, \fBargl\fR and \fBargp\fR parameters are as described for the other
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two callbacks. If the \fIdup_func()\fR returns \fB0\fR the whole \fICRYPTO_dup_ex_data()\fR
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will fail.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fICRYPTO_get_ex_new_index()\fR returns a new index or \-1 on failure.
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.PP
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\&\fICRYPTO_free_ex_index()\fR, \fICRYPTO_alloc_ex_data()\fR and \fICRYPTO_set_ex_data()\fR
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return 1 on success or 0 on failure.
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.PP
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\&\fICRYPTO_get_ex_data()\fR returns the application data or \s-1NULL\s0 on failure;
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note that \s-1NULL\s0 may be a valid value.
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.PP
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\&\fIdup_func()\fR should return 0 for failure and 1 for success.
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fICRYPTO_alloc_ex_data()\fR was added in OpenSSL 3.0.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2015\-2018 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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