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19142ef124
Reviewed-by: Tomas Mraz <tomas@openssl.org> Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/19703)
201 lines
8.1 KiB
Plaintext
201 lines
8.1 KiB
Plaintext
=pod
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=head1 NAME
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SSL_get_error - obtain result code for TLS/SSL I/O operation
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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int SSL_get_error(const SSL *ssl, int ret);
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=head1 DESCRIPTION
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SSL_get_error() returns a result code (suitable for the C "switch"
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statement) for a preceding call to SSL_connect(), SSL_accept(), SSL_do_handshake(),
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SSL_read_ex(), SSL_read(), SSL_peek_ex(), SSL_peek(), SSL_shutdown(),
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SSL_write_ex() or SSL_write() on B<ssl>. The value returned by that TLS/SSL I/O
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function must be passed to SSL_get_error() in parameter B<ret>.
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In addition to B<ssl> and B<ret>, SSL_get_error() inspects the
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current thread's OpenSSL error queue. Thus, SSL_get_error() must be
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used in the same thread that performed the TLS/SSL I/O operation, and no
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other OpenSSL function calls should appear in between. The current
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thread's error queue must be empty before the TLS/SSL I/O operation is
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attempted, or SSL_get_error() will not work reliably.
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=head1 NOTES
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Some TLS implementations do not send a close_notify alert on shutdown.
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On an unexpected EOF, versions before OpenSSL 3.0 returned
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B<SSL_ERROR_SYSCALL>, nothing was added to the error stack, and errno was 0.
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Since OpenSSL 3.0 the returned error is B<SSL_ERROR_SSL> with a meaningful
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error on the error stack.
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=head1 RETURN VALUES
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The following return values can currently occur:
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=over 4
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=item SSL_ERROR_NONE
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The TLS/SSL I/O operation completed. This result code is returned
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if and only if B<ret E<gt> 0>.
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=item SSL_ERROR_ZERO_RETURN
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The TLS/SSL peer has closed the connection for writing by sending the
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close_notify alert.
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No more data can be read.
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Note that B<SSL_ERROR_ZERO_RETURN> does not necessarily
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indicate that the underlying transport has been closed.
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This error can also appear when the option B<SSL_OP_IGNORE_UNEXPECTED_EOF>
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is set. See L<SSL_CTX_set_options(3)> for more details.
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=item SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE
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The operation did not complete and can be retried later.
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For non-QUIC SSL objects, B<SSL_ERROR_WANT_READ> is returned when the last
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operation was a read operation from a nonblocking B<BIO>.
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It means that not enough data was available at this time to complete the
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operation.
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If at a later time the underlying B<BIO> has data available for reading the same
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function can be called again.
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SSL_read() and SSL_read_ex() can also set B<SSL_ERROR_WANT_READ> when there is
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still unprocessed data available at either the B<SSL> or the B<BIO> layer, even
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for a blocking B<BIO>.
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See L<SSL_read(3)> for more information.
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For non-QUIC SSL objects, B<SSL_ERROR_WANT_WRITE> is returned when the last
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operation was a write to a nonblocking B<BIO> and it was unable to sent all data
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to the B<BIO>. When the B<BIO> is writable again, the same function can be
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called again.
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Note that the retry may again lead to an B<SSL_ERROR_WANT_READ> or
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B<SSL_ERROR_WANT_WRITE> condition.
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There is no fixed upper limit for the number of iterations that
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may be necessary until progress becomes visible at application
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protocol level.
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For QUIC SSL objects, the meaning of B<SSL_ERROR_WANT_READ> and
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B<SSL_ERROR_WANT_WRITE> have different but largely compatible semantics. Since
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QUIC implements its own flow control and uses UDP datagrams, backpressure
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conditions in terms of the underlying BIO providing network I/O are not directly
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relevant to the circumstances in which these errors are produced. In particular,
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B<SSL_ERROR_WANT_WRITE> indicates that the OpenSSL internal send buffer for a
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given QUIC stream has been filled. Likewise, B<SSL_ERROR_WANT_READ> indicates
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that the OpenSSL internal receive buffer for a given QUIC stream is empty.
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It is safe to call SSL_read() or SSL_read_ex() when more data is available
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even when the call that set this error was an SSL_write() or SSL_write_ex().
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However, if the call was an SSL_write() or SSL_write_ex(), it should be called
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again to continue sending the application data. If you get B<SSL_ERROR_WANT_WRITE>
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from SSL_write() or SSL_write_ex() then you should not do any other operation
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that could trigger B<IO> other than to repeat the previous SSL_write() call.
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For socket B<BIO>s (e.g. when SSL_set_fd() was used), select() or
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poll() on the underlying socket can be used to find out when the
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TLS/SSL I/O function should be retried.
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Caveat: Any TLS/SSL I/O function can lead to either of
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B<SSL_ERROR_WANT_READ> and B<SSL_ERROR_WANT_WRITE>.
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In particular,
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SSL_read_ex(), SSL_read(), SSL_peek_ex(), or SSL_peek() may want to write data
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and SSL_write() or SSL_write_ex() may want to read data.
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This is mainly because
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TLS/SSL handshakes may occur at any time during the protocol (initiated by
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either the client or the server); SSL_read_ex(), SSL_read(), SSL_peek_ex(),
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SSL_peek(), SSL_write_ex(), and SSL_write() will handle any pending handshakes.
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=item SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT
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The operation did not complete; the same TLS/SSL I/O function should be
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called again later. The underlying BIO was not connected yet to the peer
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and the call would block in connect()/accept(). The SSL function should be
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called again when the connection is established. These messages can only
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appear with a BIO_s_connect() or BIO_s_accept() BIO, respectively.
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In order to find out, when the connection has been successfully established,
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on many platforms select() or poll() for writing on the socket file descriptor
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can be used.
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=item SSL_ERROR_WANT_X509_LOOKUP
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The operation did not complete because an application callback set by
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SSL_CTX_set_client_cert_cb() has asked to be called again.
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The TLS/SSL I/O function should be called again later.
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Details depend on the application.
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=item SSL_ERROR_WANT_ASYNC
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The operation did not complete because an asynchronous engine is still
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processing data. This will only occur if the mode has been set to SSL_MODE_ASYNC
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using L<SSL_CTX_set_mode(3)> or L<SSL_set_mode(3)> and an asynchronous capable
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engine is being used. An application can determine whether the engine has
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completed its processing using select() or poll() on the asynchronous wait file
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descriptor. This file descriptor is available by calling
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L<SSL_get_all_async_fds(3)> or L<SSL_get_changed_async_fds(3)>. The TLS/SSL I/O
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function should be called again later. The function B<must> be called from the
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same thread that the original call was made from.
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=item SSL_ERROR_WANT_ASYNC_JOB
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The asynchronous job could not be started because there were no async jobs
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available in the pool (see ASYNC_init_thread(3)). This will only occur if the
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mode has been set to SSL_MODE_ASYNC using L<SSL_CTX_set_mode(3)> or
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L<SSL_set_mode(3)> and a maximum limit has been set on the async job pool
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through a call to L<ASYNC_init_thread(3)>. The application should retry the
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operation after a currently executing asynchronous operation for the current
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thread has completed.
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=item SSL_ERROR_WANT_CLIENT_HELLO_CB
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The operation did not complete because an application callback set by
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SSL_CTX_set_client_hello_cb() has asked to be called again.
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The TLS/SSL I/O function should be called again later.
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Details depend on the application.
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=item SSL_ERROR_SYSCALL
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Some non-recoverable, fatal I/O error occurred. The OpenSSL error queue may
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contain more information on the error. For socket I/O on Unix systems, consult
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B<errno> for details. If this error occurs then no further I/O operations should
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be performed on the connection and SSL_shutdown() must not be called.
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This value can also be returned for other errors, check the error queue for
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details.
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=item SSL_ERROR_SSL
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A non-recoverable, fatal error in the SSL library occurred, usually a protocol
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error. The OpenSSL error queue contains more information on the error. If this
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error occurs then no further I/O operations should be performed on the
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connection and SSL_shutdown() must not be called.
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=back
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=head1 SEE ALSO
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L<ssl(7)>
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=head1 HISTORY
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The SSL_ERROR_WANT_ASYNC error code was added in OpenSSL 1.1.0.
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The SSL_ERROR_WANT_CLIENT_HELLO_CB error code was added in OpenSSL 1.1.1.
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=head1 COPYRIGHT
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Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). 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 LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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