rpcsec_gss

- security flavor incorporating GSS-API protections

Synopsis

cc [ flag... ] file...  -lnsl [ library... ]
#include <rpc/rpcsec_gss.h> 

Description

RPCSEC_GSS is a security flavor which sits "on top" of the GSS-API (Generic Security Service API) for network transmissions. Applications using RPCSEC_GSS can take advantage of GSS-API security features; moreover, they can use any security mechanism (such as RSA public key or Kerberos) that works with the GSS-API.

The GSS-API offers two security services beyond the traditional authentication services (AUTH_DH, AUTH_SYS, and AUTH_KERB): integrity and privacy. With integrity, the system uses cryptographic checksumming to ensure the authenticity of a message (authenticity of originator, recipient, and data); privacy provides additional security by encrypting data. Applications using RPCSEC_GSS specify which service they wish to use. Type of security service is mechanism-independent.

Before exchanging data with a peer, an application must establish a context for the exchange. RPCSEC_GSS provides a single function for this purpose, rpc_gss_seccreate(), which allows the application to specify the security mechanism, Quality of Protection (QOP), and type of service at context creation. (The QOP parameter sets the cryptographic algorithms to be used with integrity or privacy, and is mechanism-dependent.) Once a context is established, applications can reset the QOP and type of service for each data unit exchanged, if desired.

Valid mechanisms and QOPs may be obtained from configuration files or from the name service. Each mechanism has a default QOP.

Contexts are destroyed with the usual RPC auth_destroy() call.

Data Structures

Some of the data structures used by the RPCSEC_GSS package are shown below.

This enum defines the types of security services the context may have. rpc_gss_seccreate() takes this as one argument when setting the service type for a session.

typedef enum {
   rpc_gss_svc_default = 0,
   rpc_gss_svc_none = 1,
   rpc_gss_svc_integrity = 2,
   rpc_gss_svc_privacy = 3
} rpc_gss_service_t ;

Structure containing options passed directly through to the GSS-API. rpc_gss_seccreate() takes this as an argument when creating a context.

typedef struct {
   int  req_flags;            /*GSS request bits */   
   int  time_req;           /*requested credential lifetime */ 
   gss_cred_id_t  my_cred;  /*GSS credential struct*/ 
   gss_channel_bindings_t; 
   input_channel_bindings;
} rpc_gss_options_req_t ;

This data type is used by in-kernel RPC routines, and thus is mentioned here for informational purposes only.

typedef struct {
   u_int    length;            
   void    *elements        
} *rpc_gss_OID;

Structure containing GSS-API options returned to the calling function, rpc_gss_seccreate(). MAX_GSS_MECH is defined as 128.

typedef struct {
   int           major_status;
   int           minor_status;
   u_int         rpcsec_version                  /*vers. of RPCSEC_GSS */
   int           ret_flags
   int           time_req
   gss_ctx_id_t  gss_context;
   char          actual_mechanism[MAX_GSS_MECH]; /*mechanism used*/
} rpc_gss_options_ret_t;

The (mechanism-dependent, opaque) client principal type. Used as an argument to the rpc_gss_get_principal_name() function, and in the gsscred table. Also referenced by the rpc_gss_rawcred_t structure for raw credentials (see below).

typedef struct {
   int len;            
   char name[1];    
} *rpc_gss_principal_t;

Structure for raw credentials. Used by rpc_gss_getcred() and rpc_gss_set_callback().

typedef struct {
   u_int                version;          /*RPC version # */ 
   char                 *mechanism;       /*security mechanism*/  
   char                 *qop;             /*Quality of Protection*/  
   rpc_gss_principal_t  client_principal; /*client name*/  
   char                 *svc_principal;   /*server name*/  
   rpc_gss_service_t    service;          /*service (integrity, etc.)*/
} rpc_gss_rawcred_t;

Structure for UNIX credentials. Used by rpc_gss_getcred() as an alternative to rpc_gss_rawcred_t.

typedef struct { 
   uid_t  uid;      /*user ID*/
   gid_t  gid;      /*group ID*/ 
   short  gidlen;        
   git_t  *gidlist; /*list of groups*/
} rpc_gss_ucred_t;

Callback structure used by rpc_gss_set_callback().

typedef struct {
   u_int   program;       /*RPC program #*/   
   u_int   version;       /*RPC version #*/   
   bool_t  (*callback)(); /*user-defined callback routine*/
} rpc_gss_callback_t;

Structure used by a callback routine to enforce a particular QOP and service for a session. The locked field is normally set to FALSE; the server sets it to TRUE in order to lock the session. (A locked context will reject all requests having different QOP and service values than those found in the raw_cred structure.) For more information, see the rpc_gss_set_callback(3NSL) man page.

typedef struct {
   bool_t                 locked;
   rpc_gss_rawcred_t      *raw_cred;
} rpc_gss_lock_t;

Structure used by rpc_gss_get_error() to fetch an error code when a RPCSEC_GSS routine fails.

typedef struct {
   int  rpc_gss_error;
   int  system_error;    /*same as errno*/
} rpc_gss_error_t;

Index to Routines

The following lists RPCSEC_GSS routines and the manual reference pages on which they are described. An (S) indicates it is a server-side function:

Routine (Manual Page)

Description

rpc_gss_seccreate(3NSL)

Create a secure RPCSEC_GSS context

rpc_gss_set_defaults(3NSL)

Switch service, QOP for a session

rpc_gss_max_data_length(3NSL)

Get maximum data length allowed by transport

rpc_gss_set_svc_name(3NSL)

Set server's principal name (S)

rpc_gss_getcred(3NSL)

Get credentials of caller (S)

rpc_gss_set_callback(3NSL)

Specify callback to see context use (S)

rpc_gss_get_principal_name(3NSL)

Get client principal name (S)

rpc_gss_svc_max_data_length(3NSL)

Get maximum data length allowed by transport (S)

rpc_gss_get_error(3NSL)

Get error number

rpc_gss_get_mechanisms(3NSL)

Get valid mechanism strings

rpc_gss_get_mech_info(3NSL)

Get valid QOP strings, current service

rpc_gss_get_versions(3NSL)

Get supported RPCSEC_GSS versions

rpc_gss_is_installed(3NSL)

Checks if a mechanism is installed

rpc_gss_mech_to_oid(3NSL)

Maps ASCII mechanism to OID representation

rpc_gss_qop_to_num(3NSL)

Maps ASCII QOP, mechansim to u_int number

Utilities

The gsscred utility manages the gsscred table, which contains mappings of principal names between network and local credentials. See gsscred(1M).

Files

/etc/gss/mech

List of installed mechanisms

/etc/gss/qop

List of valid QOPs

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

gsscred(1M), rpc(3NSL), rpc_clnt_auth(3NSL), xdr(3NSL), attributes(5), environ(5)

ONC+ Developer’s Guide

Linn, J. RFC 2743, Generic Security Service Application Program Interface Version 2, Update 1. Network Working Group. January 2000.