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VACCESS(9)		 BSD Kernel Developer's	Manual		    VACCESS(9)

     vaccess --	generate an access control decision using vnode	parameters

     #include <sys/param.h>
     #include <sys/vnode.h>

     vaccess(enum vtype	type, mode_t file_mode,	uid_t file_uid,
	 gid_t file_gid, mode_t	acc_mode, struct ucred *cred, int *privused);

     This call implements the logic for	the UNIX discretionary file security
     model common to many file systems in FreeBSD.  It accepts the vnodes type
     type, permissions via file_mode, owning UID file_uid, owning GID
     file_gid, desired access mode acc_mode, requesting	credential cred, and
     an	optional call-by-reference int pointer returning whether or not	privi-
     lege was required for successful evaluation of the	call; the privused
     pointer may be set	to NULL	by the caller in order not to be informed of
     privilege information, or it may point to an integer that will be set to
     1 if privilege is used, and 0 otherwise.

     This call is intended to support implementations of VOP_ACCESS(9),	which
     will use their own	access methods to retrieve the vnode properties, and
     then invoke vaccess() in order to perform the actual check.  Implementa-
     tions of VOP_ACCESS(9) may	choose to implement additional security	mecha-
     nisms whose results will be composed with the return value.

     The algorithm used	by vaccess() selects a component of the	file permis-
     sion bits based on	comparing the passed credential, file owner, and file
     group.  If	the credential's effective UID matches the file	owner, then
     the owner component of the	permission bits	is selected.  If the UID does
     not match,	then the credential's effective	GID, followed by additional
     groups, are compared with the file	group--if there	is a match, then the
     group component of	the permission bits is selected.  If neither the cre-
     dential UID or GIDs match the passed file owner and group,	then the other
     component of the permission bits is selected.

     Once appropriate protections are selected for the current credential, the
     requested access mode, in combination with	the vnode type,	will be	com-
     pared with	the discretionary rights available for the credential.	If the
     rights granted by discretionary protections are insufficient, then	super-
     user privilege, if	available for the credential, will also	be considered.

     vaccess() will return 0 on	success, or a non-zero error value on failure.

     [EACCES]		Permission denied.  An attempt was made	to access a
			file in	a way forbidden	by its file access permis-

     [EPERM]		Operation not permitted.  An attempt was made to per-
			form an	operation limited to processes with appropri-
			ate privileges or to the owner of a file or other re-

     vaccess_acl_posix1e(9), vnode(9), VOP_ACCESS(9)

     This manual page and the current implementation of	vaccess() were written
     by	Robert Watson.

BSD				August 22, 2001				   BSD


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