NAME

gss_accept_sec_context — Accept a security context initiated by a peer application

SYNOPSIS

#include <gssapi/gssapi.h>

OM_uint32
gss_accept_sec_context(OM_uint32 *minor_status, gss_ctx_id_t *context_handle, const gss_cred_id_t acceptor_cred_handle, const gss_buffer_t input_token_buffer, const gss_channel_bindings_t input_chan_bindings, const gss_name_t *src_name, gss_OID *mech_type, gss_buffer_t output_token, OM_uint32 *ret_flags, OM_uint32 *time_rec, gss_cred_id_t *delegated_cred_handle);

DESCRIPTION

Allows a remotely initiated security context between the application and a remote peer to be established. The routine may return a output_token which should be transferred to the peer application, where the peer application will present it to gss_init_sec_context(3). If no token need be sent, gss_accept_sec_context() will indicate this by setting the length field of the output_token argument to zero. To complete the context establishment, one or more reply tokens may be required from the peer application; if so, gss_accept_sec_context() will return a status flag of GSS_S_CONTINUE_NEEDED, in which case it should be called again when the reply token is received from the peer application, passing the token to gss_accept_sec_context() via the input_token parameters.

Portable applications should be constructed to use the token length and return status to determine whether a token needs to be sent or waited for. Thus a typical portable caller should always invoke gss_accept_sec_context() within a loop:

gss_ctx_id_t context_hdl = GSS_C_NO_CONTEXT;

do {
  receive_token_from_peer(input_token);
  maj_stat = gss_accept_sec_context(&min_stat,
				    &context_hdl,
				    cred_hdl,
				    input_token,
				    input_bindings,
				    &client_name,
				    &mech_type,
				    output_token,
				    &ret_flags,
				    &time_rec,
				    &deleg_cred);
  if (GSS_ERROR(maj_stat)) {
    report_error(maj_stat, min_stat);
  };
  if (output_token->length != 0) {
    send_token_to_peer(output_token);

    gss_release_buffer(&min_stat, output_token);
  };
  if (GSS_ERROR(maj_stat)) {
    if (context_hdl != GSS_C_NO_CONTEXT)
      gss_delete_sec_context(&min_stat,
			     &context_hdl,
			     GSS_C_NO_BUFFER);
    break;
  };
} while (maj_stat & GSS_S_CONTINUE_NEEDED);

Whenever the routine returns a major status that includes the value GSS_S_CONTINUE_NEEDED, the context is not fully established and the following restrictions apply to the output parameters:

The value returned via the time_rec parameter is undefined unless the accompanying ret_flags parameter contains the bit GSS_C_PROT_READY_FLAG, indicating that per-message services may be applied in advance of a successful completion status, the value returned via the mech_type parameter may be undefined until the routine returns a major status value of GSS_S_COMPLETE.

The values of the GSS_C_DELEG_FLAG, GSS_C_MUTUAL_FLAG, GSS_C_REPLAY_FLAG, GSS_C_SEQUENCE_FLAG, GSS_C_CONF_FLAG, GSS_C_INTEG_FLAG and GSS_C_ANON_FLAG bits returned via the ret_flags parameter should contain the values that the implementation expects would be valid if context establishment were to succeed.

The values of the GSS_C_PROT_READY_FLAG and GSS_C_TRANS_FLAG bits within ret_flags should indicate the actual state at the time gss_accept_sec_context() returns, whether or not the context is fully established.

Although this requires that GSS-API implementations set the GSS_C_PROT_READY_FLAG in the final ret_flags returned to a caller (i.e. when accompanied by a GSS_S_COMPLETE status code), applications should not rely on this behavior as the flag was not defined in Version 1 of the GSS-API. Instead, applications should be prepared to use per-message services after a successful context establishment, according to the GSS_C_INTEG_FLAG and GSS_C_CONF_FLAG values.

All other bits within the ret_flags argument should be set to zero. While the routine returns GSS_S_CONTINUE_NEEDED, the values returned via the ret_flags argument indicate the services that the implementation expects to be available from the established context.

If the initial call of gss_accept_sec_context() fails, the implementation should not create a context object, and should leave the value of the context_handle parameter set to GSS_C_NO_CONTEXT to indicate this. In the event of a failure on a subsequent call, the implementation is permitted to delete the "half-built" security context (in which case it should set the context_handle parameter to GSS_C_NO_CONTEXT ), but the preferred behavior is to leave the security context (and the context_handle parameter) untouched for the application to delete (using gss_delete_sec_context(3) ).

During context establishment, the informational status bits GSS_S_OLD_TOKEN and GSS_S_DUPLICATE_TOKEN indicate fatal errors, and GSS-API mechanisms should always return them in association with a routine error of GSS_S_FAILURE. This requirement for pairing did not exist in version 1 of the GSS-API specification, so applications that wish to run over version 1 implementations must special-case these codes.

PARAMETERS

context_handle

Context handle for new context. Supply

GSS_C_NO_CONTEXT
      for first

call; use value returned in subsequent calls. Once gss_accept_sec_context() has returned a value via this parameter, resources have been assigned to the corresponding context, and must be freed by the application after use with a call to gss_delete_sec_context(3).

acceptor_cred_handle

Credential handle claimed by context acceptor. Specify GSS_C_NO_CREDENTIAL to accept the context as a default principal. If GSS_C_NO_CREDENTIAL is specified, but no default acceptor principal is defined, GSS_S_NO_CRED will be returned.

input_token_buffer

Token obtained from remote application.

input_chan_bindings

Application-specified bindings. Allows application to securely bind channel identification information to the security context. If channel bindings are not used, specify GSS_C_NO_CHANNEL_BINDINGS.

src_name

Authenticated name of context initiator. After use, this name should be deallocated by passing it to gss_release_name(3). If not required, specify NULL.

mech_type

Security mechanism used. The returned OID value will be a pointer into static storage, and should be treated as read-only by the caller (in particular, it does not need to be freed). If not required, specify NULL.

output_token

Token to be passed to peer application. If the length field of the returned token buffer is 0, then no token need be passed to the peer application. If a non-zero length field is returned, the associated storage must be freed after use by the application with a call to gss_release_buffer(3).

ret_flags

Contains various independent flags, each of which indicates that the context supports a specific service option. If not needed, specify NULL. Symbolic names are provided for each flag, and the symbolic names corresponding to the required flags should be logically-ANDed with the ret_flags value to test whether a given option is supported by the context. The flags are:

GSS_C_DELEG_FLAG

True: Delegated credentials are available via the delegated_cred_handle parameter
False: No credentials were delegated

GSS_C_MUTUAL_FLAG

True: Remote peer asked for mutual authentication
False: Remote peer did not ask for mutual authentication

GSS_C_REPLAY_FLAG

True: Replay of protected messages will be detected
False: Replayed messages will not be detected

GSS_C_SEQUENCE_FLAG

True: Out-of-sequence protected messages will be detected
False: Out-of-sequence messages will not be detected

GSS_C_CONF_FLAG

True: Confidentiality service may be invoked by calling the gss_wrap(3) routine
False: No confidentiality service (via gss_wrap(3)) available. gss_wrap(3) will provide message encapsulation, data-origin authentication and integrity services only.

GSS_C_INTEG_FLAG

True: Integrity service may be invoked by calling either gss_get_mic(3) or gss_wrap(3) routines.
False: Per-message integrity service unavailable.

GSS_C_ANON_FLAG

True: The initiator does not wish to be authenticated; the src_name parameter (if requested) contains an anonymous internal name.
False: The initiator has been authenticated normally.

GSS_C_PROT_READY_FLAG

True: Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available if the accompanying major status return value is either GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED.
False: Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available only if the accompanying major status return value is GSS_S_COMPLETE.

GSS_C_TRANS_FLAG

True: The resultant security context may be transferred to other processes via a call to gss_export_sec_context(3).
False: The security context is not transferable.

All other bits should be set to zero.

time_rec

Number of seconds for which the context will remain valid. Specify NULL if not required.

delegated_cred_handle

Credential handle for credentials received from context initiator. Only valid if GSS_C_DELEG_FLAG in ret_flags is true, in which case an explicit credential handle (i.e. not GSS_C_NO_CREDENTIAL) will be returned; if false, gss_accept_context() will set this parameter to GSS_C_NO_CREDENTIAL. If a credential handle is returned, the associated resources must be released by the application after use with a call to gss_release_cred(3). Specify NULL if not required.

minor_status

Mechanism specific status code.

RETURN VALUES

GSS_S_CONTINUE_NEEDED: Indicates that a token from the peer application is required to complete the context, and that gss_accept_sec_context must be called again with that token.
GSS_S_DEFECTIVE_TOKEN: Indicates that consistency checks performed on the input_token failed.
GSS_S_DEFECTIVE_CREDENTIAL: Indicates that consistency checks performed on the credential failed.
GSS_S_NO_CRED: The supplied credentials were not valid for context acceptance, or the credential handle did not reference any credentials.
GSS_S_CREDENTIALS_EXPIRED: The referenced credentials have expired.
GSS_S_BAD_BINDINGS: The input_token contains different channel bindings to those specified via the input_chan_bindings parameter.
GSS_S_NO_CONTEXT: Indicates that the supplied context handle did not refer to a valid context.
GSS_S_BAD_SIG: The input_token contains an invalid MIC.
GSS_S_OLD_TOKEN: The input_token was too old. This is a fatal error during context establishment.
GSS_S_DUPLICATE_TOKEN: The input_token is valid, but is a duplicate of a token already processed. This is a fatal error during context establishment.
GSS_S_BAD_MECH: The received token specified a mechanism that is not supported by the implementation or the provided credential.

STANDARDS

RFC 2743: Generic Security Service Application Program Interface Version 2, Update 1
RFC 2744: Generic Security Service API Version 2 : C-bindings

HISTORY

The gss_accept_sec_context function first appeared in FreeBSD 7.0.

AUTHORS

John Wray, Iris Associates

COPYRIGHT

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