rpcsec_gss(3N)

NAME

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 Application Programming Interface) 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_DES, 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. The 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. Validation 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.

rpc_gss_service_t

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; 

rpc_gss_options_req_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; 

rpc_gss_OID

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; 

rpc_gss_options_ret_t

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; 

rpc_gss_principal_t

The (mechanism-dependent, opaque) client principal type is 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; 

rpc_gss_rawcred_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; 

rpc_gss_ucred_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; 

rpc_gss_callback_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; 

rpc_gss_lock_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 rpc_gss_set_callback(3N).

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

rpc_gss_error_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.

RPCSEC_GSS Routines: Description
rpc_gss_seccreate(3N): Create a secure RPCSEC_GSS context.
rpc_gss_set_defaults(3N): Switch service and QOP for a session.
rpc_gss_max_data_length(3N): Get maximum data length allowed by transport.
rpc_gss_set_svc_name(3N): Set server's principal name. (S)
rpc_gss_getcred(3N): Get credentials of caller. (S)
rpc_gss_set_callback(3N): Specify callback to see context use. (S)
rpc_gss_get_principal_name(3N): Get client principal name. (S)
rpc_gss_svc_max_data_length(3N): Get maximum data length allowed by transport. (S)
rpc_gss_get_error(3N): Get error number.
rpc_gss_get_mechanisms(3N): Get valid mechanism strings.
rpc_gss_get_mech_info(3N): Get valid QOP strings for current service.
rpc_gss_get_versions(3N): Get supported RPCSEC_GSS versions.
rpc_gss_is_installed(3N): Checks if a mechanism is installed.
rpc_gss_mech_to_oid(3N): Maps ASCII mechanism to OID representation.
rpc_gss_qop_to_num(3N): Maps ASCII QOP, mechanism to u_int number.

Utilities

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

MULTITHREAD USAGE

Thread Safe:: Yes
Cancel Safe:: Yes
Fork Safe:: No
Async-cancel Safe:: No
Async-signal Safe:: No

These functions can be called safely in a multithreaded environment. They may be cancellation points in that they call functions that are cancel points.

In a multithreaded environment, these functions are not safe to be called by a child process after fork() and before exec(). These functions should not be called by a multithreaded application that supports asynchronous cancellation or asynchronous signals.

FILES

/etc/gss/mech: List of installed mechanisms.
/etc/gss/qop: List of valid QOPs.