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PRIV(9)		       FreeBSD Kernel Developer's Manual	       PRIV(9)

     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 suser(9) privilege checking interface.  Privileges typically
     represent rights in one of	two categories:	the right to manage a particu-
     lar 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 poli-
     cies: 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 com-
     plete 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 privi-
     leges 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 privi-

     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 con-

     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), suser(9),	ucred(9)

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

FreeBSD	11.0			August 30, 2006			  FreeBSD 11.0


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