161 lines
4.7 KiB
Text
161 lines
4.7 KiB
Text
=pod
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=head1 NAME
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X509_STORE_CTX_set_verify_cb - set verification callback
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=head1 SYNOPSIS
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#include <openssl/x509_vfy.h>
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void X509_STORE_CTX_set_verify_cb(X509_STORE_CTX *ctx,
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int (*verify_cb)(int ok, X509_STORE_CTX *ctx));
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=head1 DESCRIPTION
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X509_STORE_CTX_set_verify_cb() sets the verification callback of B<ctx> to
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B<verify_cb> overwriting any existing callback.
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The verification callback can be used to customise the operation of certificate
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verification, either by overriding error conditions or logging errors for
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debugging purposes.
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However a verification callback is B<not> essential and the default operation
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is often sufficient.
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The B<ok> parameter to the callback indicates the value the callback should
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return to retain the default behaviour. If it is zero then and error condition
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is indicated. If it is 1 then no error occurred. If the flag
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B<X509_V_FLAG_NOTIFY_POLICY> is set then B<ok> is set to 2 to indicate the
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policy checking is complete.
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The B<ctx> parameter to the callback is the B<X509_STORE_CTX> structure that
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is performing the verification operation. A callback can examine this
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structure and receive additional information about the error, for example
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by calling X509_STORE_CTX_get_current_cert(). Additional application data can
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be passed to the callback via the B<ex_data> mechanism.
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=head1 WARNING
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In general a verification callback should B<NOT> unconditionally return 1 in
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all circumstances because this will allow verification to succeed no matter
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what the error. This effectively removes all security from the application
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because B<any> certificate (including untrusted generated ones) will be
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accepted.
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=head1 NOTES
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The verification callback can be set and inherited from the parent structure
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performing the operation. In some cases (such as S/MIME verification) the
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B<X509_STORE_CTX> structure is created and destroyed internally and the
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only way to set a custom verification callback is by inheriting it from the
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associated B<X509_STORE>.
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=head1 RETURN VALUES
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X509_STORE_CTX_set_verify_cb() does not return a value.
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=head1 EXAMPLES
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Default callback operation:
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int verify_callback(int ok, X509_STORE_CTX *ctx)
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{
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return ok;
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}
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Simple example, suppose a certificate in the chain is expired and we wish
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to continue after this error:
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int verify_callback(int ok, X509_STORE_CTX *ctx)
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{
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/* Tolerate certificate expiration */
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if (X509_STORE_CTX_get_error(ctx) == X509_V_ERR_CERT_HAS_EXPIRED)
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return 1;
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/* Otherwise don't override */
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return ok;
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}
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More complex example, we don't wish to continue after B<any> certificate has
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expired just one specific case:
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int verify_callback(int ok, X509_STORE_CTX *ctx)
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{
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int err = X509_STORE_CTX_get_error(ctx);
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X509 *err_cert = X509_STORE_CTX_get_current_cert(ctx);
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if (err == X509_V_ERR_CERT_HAS_EXPIRED)
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{
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if (check_is_acceptable_expired_cert(err_cert)
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return 1;
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}
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return ok;
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}
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Full featured logging callback. In this case the B<bio_err> is assumed to be
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a global logging B<BIO>, an alternative would to store a BIO in B<ctx> using
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B<ex_data>.
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int verify_callback(int ok, X509_STORE_CTX *ctx)
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{
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X509 *err_cert;
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int err,depth;
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err_cert = X509_STORE_CTX_get_current_cert(ctx);
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err = X509_STORE_CTX_get_error(ctx);
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depth = X509_STORE_CTX_get_error_depth(ctx);
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BIO_printf(bio_err,"depth=%d ",depth);
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if (err_cert)
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{
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X509_NAME_print_ex(bio_err, X509_get_subject_name(err_cert),
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0, XN_FLAG_ONELINE);
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BIO_puts(bio_err, "\n");
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}
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else
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BIO_puts(bio_err, "<no cert>\n");
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if (!ok)
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BIO_printf(bio_err,"verify error:num=%d:%s\n",err,
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X509_verify_cert_error_string(err));
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switch (err)
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{
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case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
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BIO_puts(bio_err,"issuer= ");
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X509_NAME_print_ex(bio_err, X509_get_issuer_name(err_cert),
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0, XN_FLAG_ONELINE);
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BIO_puts(bio_err, "\n");
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break;
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case X509_V_ERR_CERT_NOT_YET_VALID:
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case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
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BIO_printf(bio_err,"notBefore=");
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ASN1_TIME_print(bio_err,X509_get_notBefore(err_cert));
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BIO_printf(bio_err,"\n");
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break;
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case X509_V_ERR_CERT_HAS_EXPIRED:
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case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
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BIO_printf(bio_err,"notAfter=");
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ASN1_TIME_print(bio_err,X509_get_notAfter(err_cert));
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BIO_printf(bio_err,"\n");
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break;
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case X509_V_ERR_NO_EXPLICIT_POLICY:
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policies_print(bio_err, ctx);
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break;
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}
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if (err == X509_V_OK && ok == 2)
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/* print out policies */
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BIO_printf(bio_err,"verify return:%d\n",ok);
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return(ok);
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}
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=head1 SEE ALSO
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L<X509_STORE_CTX_get_error(3)|X509_STORE_CTX_get_error(3)>
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L<X509_STORE_set_verify_cb_func(3)|X509_STORE_set_verify_cb_func(3)>
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L<X509_STORE_CTX_get_ex_new_index(3)|X509_STORE_CTX_get_ex_new_index(3)>
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=head1 HISTORY
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X509_STORE_CTX_set_verify_cb() is available in all versions of SSLeay and
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OpenSSL.
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=cut
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