Commit 6b1bb98f authored by Benjamin Kaduk's avatar Benjamin Kaduk Committed by Richard Levitte
Browse files

Add SSL_CTX early callback 



Provide a callback interface that gives the application the ability
to adjust the nascent SSL object at the earliest stage of ClientHello
processing, immediately after extensions have been collected but
before they have been processed.

This is akin to BoringSSL's "select_certificate_cb" (though it is not
API compatible), and as the name indicates, one major use is to examine
the supplied server name indication and select what certificate to
present to the client.  However, it can also be used to make more
sweeping configuration changes to the SSL object according to the
selected server identity and configuration.  That may include adjusting
the permitted TLS versions, swapping out the SSL_CTX object (as is
traditionally done in a tlsext_servername_callback), changing the
server's cipher list, and more.

We also wish to allow an early callback to indicate that it needs to perform
additional work asynchronously and resume processing later.  To that effect,
refactor the second half of tls_process_client_hello() into a subroutine to be
called at the post-processing stage (including the early callback itself), to
allow the callback to result in remaining in the same work stage for a later
call to succeed.  This requires allocating for and storing the CLIENTHELLO_MSG
in the SSL object to be preserved across such calls, but the storage is
reclaimed after ClientHello processing finishes.

Information about the CliehtHello is available to the callback by means of
accessor functions that can only be used from the early callback.  This allows
extensions to make use of the existing internal parsing machinery without
exposing structure internals (e.g., of PACKET), so that applications do not
have to write fragile parsing code.

Applications are encouraged to utilize an early callback and not use
a servername_callback, in order to avoid unexpected behavior that
occurs due to the relative order of processing between things like
session resumption and the historical servername callback.

Also tidy up nearby style by removing unnecessary braces around one-line
conditional bodies.

Reviewed-by: default avatarMatt Caswell <matt@openssl.org>
Reviewed-by: default avatarRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2279)
parent ddf97258

doc/man3/SSL_CTX_set_early_cb.pod

0 → 100644
+110 −0
Original line number Original line Diff line number Diff line 
=pod



=head1 NAME



SSL_CTX_set_early_cb, SSL_early_cb_fn, SSL_early_isv2, SSL_early_get0_legacy_version, SSL_early_get0_random, SSL_early_get0_session_id, SSL_early_get0_ciphers, SSL_early_get0_compression_methods, SSL_early_get0_ext - callback functions for early server-side ClientHello processing



=head1 SYNOPSIS



 typedef int (*SSL_early_cb_fn)(SSL *s, int *al, void *arg);

 void SSL_CTX_set_early_cb(SSL_CTX *c, SSL_early_cb_fn *f, void *arg);

 int SSL_early_isv2(SSL *s);

 unsigned int SSL_early_get0_legacy_version(SSL *s);

 size_t SSL_early_get0_random(SSL *s, const unsigned char **out);

 size_t SSL_early_get0_session_id(SSL *s, const unsigned char **out);

 size_t SSL_early_get0_ciphers(SSL *s, const unsigned char **out);

 size_t SSL_early_get0_compression_methods(SSL *s, const unsigned char **out);

 int SSL_early_get0_ext(SSL *s, int type, const unsigned char **out,

                        size_t *outlen);



=head1 DESCRIPTION



SSL_CTX_set_early_cb() sets the callback function, which is automatically

called during the early stages of ClientHello processing on the server.

The argument supplied when setting the callback is passed back to the

callback at runtime.  A callback that returns failure (0) will cause the

connection to terminate, and callbacks returning failure should indicate

what alert value is to be sent in the B<al> parameter.  A callback may

also return a negative value to suspend the handshake, and the handshake

function will return immediately.  L<SSL_get_error(3)> will return

SSL_ERROR_WANT_EARLY to indicate that the handshake was suspended.

It is the job of the early callback to store information about the state

of the last call if needed to continue.  On the next call into the handshake

function, the early callback will be called again, and, if it returns

success, normal handshake processing will continue from that point.



SSL_early_isv2() indicates whether the ClientHello was carried in a

SSLv2 record and is in the SSLv2 format.  The SSLv2 format has substantial

differences from the normal SSLv3 format, including using three bytes per

cipher suite, and not allowing extensions.  Additionally, the SSLv2 format

'challenge' field is exposed via SSL_early_get0_random(), padded to

SSL3_RANDOM_SIZE bytes with zeros if needed.  For SSLv2 format ClientHellos,

SSL_early_get0_compression_methods() returns a dummy list that only includes

the null compression method, since the SSLv2 format does not include a

mechanism by which to negotiate compression.



SSL_early_get0_random(), SSL_early_get0_session_id(), SSL_early_get0_ciphers(),

and SSL_early_get0_compression_methods() provide access to the corresponding

ClientHello fields, returning the field length and optionally setting an

out pointer to the octets of that field.



Similarly, SSL_early_get0_ext() provides access to individual extensions

from the ClientHello on a per-extension basis.  For the provided wire

protocol extension type value, the extension value and length are returned

in the output parameters (if present).



=head1 NOTES



The early callback provides a vast window of possibilities for application

code to affect the TLS handshake.  A primary use of the callback is to

allow the server to examine the server name indication extension provided

by the client in order to select an appropriate certificate to present,

and make other configuration adjustments relevant to that server name

and its configuration.  Such configuration changes can include swapping out

the associated SSL_CTX pointer, modifying the server's list of permitted TLS

versions, changing the server's cipher list, etc.



It is also recommended that applications utilize an early callback and

not use a servername callback, in order to avoid unexpected behavior that

occurs due to the relative order of processing between things like session

resumption and the historical servername callback.



The SSL_early_* family of functions may only be called from code executing

within an early callback.



=head1 RETURN VALUES



The application's supplied early callback returns 1 on success, 0 on failure,

and a negative value to suspend processing.



SSL_early_isv2() returns 1 for SSLv2-format ClientHellos and 0 otherwise.



SSL_early_get0_random(), SSL_early_get0_session_id(), SSL_early_get0_ciphers(),

and SSL_early_get0_compression_methods() return the length of the corresponding

ClientHello fields.  If zero is returned, the ouput pointer should not be

assumed to be valid.



SSL_early_get0_ext() returns 1 if the extension of type 'type' is present, and

0 otherwise.



=head1 SEE ALSO



L<ssl(7)>, L<SSL_CTX_set_tlsext_servername_callback(3)>



=head1 HISTORY



The SSL early callback, SSL_early_isv2(), SSL_early_get0_random(),

SSL_early_get0_session_id(), SSL_early_get0_ciphers(),

SSL_early_get0_compression_methods(), and SSL_early_get0_ext() were

added in OpenSSL 1.1.1.



=head1 COPYRIGHT



Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.



Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

in the file LICENSE in the source distribution or at

L<https://www.openssl.org/source/license.html>.



=cut

doc/man3/SSL_get_error.pod

+9 −1
Original line number Original line Diff line number Diff line
@@ -110,6 +110,13 @@ through a call to L<ASYNC_init_thread(3)>. The application should retry the 
operation after a currently executing asynchronous operation for the current

operation after a currently executing asynchronous operation for the current

thread has completed.

thread has completed.





=item SSL_ERROR_WANT_EARLY



The operation did not complete because an application callback set by

SSL_CTX_set_early_cb() has asked to be called again.

The TLS/SSL I/O function should be called again later.

Details depend on the application.



=item SSL_ERROR_SYSCALL

=item SSL_ERROR_SYSCALL





Some non-recoverable I/O error occurred.

Some non-recoverable I/O error occurred.
@@ -130,10 +137,11 @@ L<ssl(7)>, L<err(7)> 
=head1 HISTORY

=head1 HISTORY





SSL_ERROR_WANT_ASYNC was added in OpenSSL 1.1.0.

SSL_ERROR_WANT_ASYNC was added in OpenSSL 1.1.0.

SSL_ERROR_WANT_EARLY was added in OpenSSL 1.1.1.





=head1 COPYRIGHT

=head1 COPYRIGHT





Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.





Licensed under the OpenSSL license (the "License").  You may not use

Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

this file except in compliance with the License.  You can obtain a copy

doc/man3/SSL_want.pod

+17 −5
Original line number Original line Diff line number Diff line
@@ -3,8 +3,8 @@ 
=head1 NAME

=head1 NAME





SSL_want, SSL_want_nothing, SSL_want_read, SSL_want_write, SSL_want_x509_lookup,

SSL_want, SSL_want_nothing, SSL_want_read, SSL_want_write, SSL_want_x509_lookup,

SSL_want_async, SSL_want_async_job - obtain state information TLS/SSL I/O

SSL_want_async, SSL_want_async_job, SSL_want_early - obtain state information

operation

TLS/SSL I/O operation





=head1 SYNOPSIS

=head1 SYNOPSIS
@@ -17,6 +17,7 @@ operation 
 int SSL_want_x509_lookup(const SSL *ssl);

 int SSL_want_x509_lookup(const SSL *ssl);

 int SSL_want_async(const SSL *ssl);

 int SSL_want_async(const SSL *ssl);

 int SSL_want_async_job(const SSL *ssl);

 int SSL_want_async_job(const SSL *ssl);

 int SSL_want_early(const SSL *ssl);





=head1 DESCRIPTION

=head1 DESCRIPTION
@@ -81,19 +82,30 @@ The asynchronous job could not be started because there were no async jobs 
available in the pool (see ASYNC_init_thread(3)). A call to L<SSL_get_error(3)>

available in the pool (see ASYNC_init_thread(3)). A call to L<SSL_get_error(3)>

should return SSL_ERROR_WANT_ASYNC_JOB.

should return SSL_ERROR_WANT_ASYNC_JOB.





=item SSL_EARLY_WORK



The operation did not complete because an application callback set by

SSL_CTX_set_early_cb() has asked to be called again.

A call to L<SSL_get_error(3)> should return

SSL_ERROR_WANT_EARLY.



=back

=back





SSL_want_nothing(), SSL_want_read(), SSL_want_write(), SSL_want_x509_lookup(),

SSL_want_nothing(), SSL_want_read(), SSL_want_write(), SSL_want_x509_lookup(),

SSL_want_async() and SSL_want_async_job() return 1, when the corresponding

SSL_want_async(), SSL_want_async_job(), and SSL_want_early() return 1, when

condition is true or 0 otherwise.

the corresponding condition is true or 0 otherwise.





=head1 SEE ALSO

=head1 SEE ALSO





L<ssl(7)>, L<err(7)>, L<SSL_get_error(3)>

L<ssl(7)>, L<err(7)>, L<SSL_get_error(3)>





=head1 HISTORY



SSL_want_early() and SSL_EARLY_WORK were added in OpenSSL 1.1.1.



=head1 COPYRIGHT

=head1 COPYRIGHT





Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.

Copyright 2001-2017 The OpenSSL Project Authors. All Rights Reserved.





Licensed under the OpenSSL license (the "License").  You may not use

Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

this file except in compliance with the License.  You can obtain a copy

include/openssl/ssl.h

+18 −0
Original line number Original line Diff line number Diff line
@@ -764,6 +764,7 @@ __owur int SSL_extension_supported(unsigned int ext_type); 
# define SSL_X509_LOOKUP        4

# define SSL_X509_LOOKUP        4

# define SSL_ASYNC_PAUSED       5

# define SSL_ASYNC_PAUSED       5

# define SSL_ASYNC_NO_JOBS      6

# define SSL_ASYNC_NO_JOBS      6

# define SSL_EARLY_WORK         7





/* These will only be used when doing non-blocking IO */

/* These will only be used when doing non-blocking IO */

# define SSL_want_nothing(s)     (SSL_want(s) == SSL_NOTHING)

# define SSL_want_nothing(s)     (SSL_want(s) == SSL_NOTHING)
@@ -772,6 +773,7 @@ __owur int SSL_extension_supported(unsigned int ext_type); 
# define SSL_want_x509_lookup(s) (SSL_want(s) == SSL_X509_LOOKUP)

# define SSL_want_x509_lookup(s) (SSL_want(s) == SSL_X509_LOOKUP)

# define SSL_want_async(s)       (SSL_want(s) == SSL_ASYNC_PAUSED)

# define SSL_want_async(s)       (SSL_want(s) == SSL_ASYNC_PAUSED)

# define SSL_want_async_job(s)   (SSL_want(s) == SSL_ASYNC_NO_JOBS)

# define SSL_want_async_job(s)   (SSL_want(s) == SSL_ASYNC_NO_JOBS)

# define SSL_want_early(s)       (SSL_want(s) == SSL_EARLY_WORK)





# define SSL_MAC_FLAG_READ_MAC_STREAM 1

# define SSL_MAC_FLAG_READ_MAC_STREAM 1

# define SSL_MAC_FLAG_WRITE_MAC_STREAM 2

# define SSL_MAC_FLAG_WRITE_MAC_STREAM 2
@@ -1041,6 +1043,7 @@ DECLARE_PEM_rw(SSL_SESSION, SSL_SESSION) 
# define SSL_ERROR_WANT_ACCEPT           8

# define SSL_ERROR_WANT_ACCEPT           8

# define SSL_ERROR_WANT_ASYNC            9

# define SSL_ERROR_WANT_ASYNC            9

# define SSL_ERROR_WANT_ASYNC_JOB       10

# define SSL_ERROR_WANT_ASYNC_JOB       10

# define SSL_ERROR_WANT_EARLY           11

# define SSL_CTRL_SET_TMP_DH                     3

# define SSL_CTRL_SET_TMP_DH                     3

# define SSL_CTRL_SET_TMP_ECDH                   4

# define SSL_CTRL_SET_TMP_ECDH                   4

# define SSL_CTRL_SET_TMP_DH_CB                  6

# define SSL_CTRL_SET_TMP_DH_CB                  6
@@ -1572,6 +1575,20 @@ __owur char *SSL_get_srp_username(SSL *s); 
__owur char *SSL_get_srp_userinfo(SSL *s);

__owur char *SSL_get_srp_userinfo(SSL *s);

# endif

# endif





/*

 * Early callback and helpers.

 */

typedef int (*SSL_early_cb_fn) (SSL *s, int *al, void *arg);

void SSL_CTX_set_early_cb(SSL_CTX *c, SSL_early_cb_fn cb, void *arg);

int SSL_early_isv2(SSL *s);

unsigned int SSL_early_get0_legacy_version(SSL *s);

size_t SSL_early_get0_random(SSL *s, const unsigned char **out);

size_t SSL_early_get0_session_id(SSL *s, const unsigned char **out);

size_t SSL_early_get0_ciphers(SSL *s, const unsigned char **out);

size_t SSL_early_get0_compression_methods(SSL *s, const unsigned char **out);

int SSL_early_get0_ext(SSL *s, unsigned int type, const unsigned char **out,

                       size_t *outlen);



void SSL_certs_clear(SSL *s);

void SSL_certs_clear(SSL *s);

void SSL_free(SSL *ssl);

void SSL_free(SSL *ssl);

# ifdef OSSL_ASYNC_FD

# ifdef OSSL_ASYNC_FD
@@ -2348,6 +2365,7 @@ int ERR_load_SSL_strings(void); 
# define SSL_F_TLS_CONSTRUCT_STOC_SESSION_TICKET          460

# define SSL_F_TLS_CONSTRUCT_STOC_SESSION_TICKET          460

# define SSL_F_TLS_CONSTRUCT_STOC_STATUS_REQUEST          461

# define SSL_F_TLS_CONSTRUCT_STOC_STATUS_REQUEST          461

# define SSL_F_TLS_CONSTRUCT_STOC_USE_SRTP                462

# define SSL_F_TLS_CONSTRUCT_STOC_USE_SRTP                462

# define SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO        521

# define SSL_F_TLS_GET_MESSAGE_BODY                       351

# define SSL_F_TLS_GET_MESSAGE_BODY                       351

# define SSL_F_TLS_GET_MESSAGE_HEADER                     387

# define SSL_F_TLS_GET_MESSAGE_HEADER                     387

# define SSL_F_TLS_PARSE_CLIENTHELLO_TLSEXT               449

# define SSL_F_TLS_PARSE_CLIENTHELLO_TLSEXT               449

ssl/ssl_err.c

+2 −0
Original line number Original line Diff line number Diff line
@@ -376,6 +376,8 @@ static ERR_STRING_DATA SSL_str_functs[] = { 
     "tls_construct_stoc_status_request"},

     "tls_construct_stoc_status_request"},

    {ERR_FUNC(SSL_F_TLS_CONSTRUCT_STOC_USE_SRTP),

    {ERR_FUNC(SSL_F_TLS_CONSTRUCT_STOC_USE_SRTP),

     "tls_construct_stoc_use_srtp"},

     "tls_construct_stoc_use_srtp"},

    {ERR_FUNC(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO),

     "tls_early_post_process_client_hello"},

    {ERR_FUNC(SSL_F_TLS_GET_MESSAGE_BODY), "tls_get_message_body"},

    {ERR_FUNC(SSL_F_TLS_GET_MESSAGE_BODY), "tls_get_message_body"},

    {ERR_FUNC(SSL_F_TLS_GET_MESSAGE_HEADER), "tls_get_message_header"},

    {ERR_FUNC(SSL_F_TLS_GET_MESSAGE_HEADER), "tls_get_message_header"},

    {ERR_FUNC(SSL_F_TLS_PARSE_CLIENTHELLO_TLSEXT),

    {ERR_FUNC(SSL_F_TLS_PARSE_CLIENTHELLO_TLSEXT),