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     priv — kernel privilege checking API


     #include <sys/priv.h>

     priv_check(struct thread *td, int priv);

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


     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).


     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


     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

     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.


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


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