focal (9) priv.9freebsd.gz

NAME

     priv — kernel privilege checking API

SYNOPSIS

     #include <sys/priv.h>

     int
     priv_check(struct thread *td, int priv);

     int
     priv_check_cred(struct ucred *cred, int priv, int flags);

DESCRIPTION

     The priv interfaces check to see if specific system privileges are granted to the passed thread, td, or
     credential, cred.  This interface replaces the now removed suser(9) privilege checking interface.
     Privileges typically represent rights in one of two categories: the right to manage a particular component
     of the system, or an exemption to a specific policy or access control list.  The caller identifies the
     desired privilege via the priv argument.  The optional flags argument, flags, is currently unused.

   Privilege Policies
     Privileges are typically granted based on one of two base system policies: the superuser policy, which
     grants privilege based on the effective (or sometimes real) UID having a value of 0, and the jail(2)
     policy, which permits only certain privileges to be granted to processes in a jail.  The set of available
     privileges may also be influenced by the TrustedBSD MAC Framework, described in mac(9).

IMPLEMENTATION NOTES

     When adding a new privilege check to a code path, first check the complete list of current privileges in
     sys/priv.h to see if one already exists for the class of privilege required.  Only if there is not an exact
     match should a new privilege be added to the privilege list.  As privilege numbers becomes encoded in the
     kernel module ABI, privilege constants must not be changed as any kernel modules depending on privileges
     will then need to be recompiled.  When adding a new privilege, be certain to also determine whether it
     should be listed in prison_priv_check(), which includes a complete list of privileges granted to the root
     user in jail(2).

     Certain catch-all privileges exist, such as PRIV_DRIVER, intended to be used by device drivers, rather than
     adding a new driver-specific privilege.

RETURN VALUES

     Typically, 0 will be returned for success, and EPERM will be returned on failure.  Most consumers of priv
     will wish to directly return the error code from a failed privilege check to user space; a small number
     will wish to translate it to another error code appropriate to a specific context.

     When designing new APIs, it is preferable to return explicit errors from a call if privilege is not granted
     rather than changing the semantics of the call but returning success.  For example, the behavior exhibited
     by stat(2), in which the generation field is optionally zero'd out when there is insufficient privilege is
     highly undesirable, as it results in frequent privilege checks, and the caller is unable to tell if an
     access control failure occurred.

SEE ALSO

     jail(2), mac(9), ucred(9)

AUTHORS

     The priv API and implementation were created by Robert Watson under contract to nCircle Network Security,
     Inc.