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NAME
     vaccess - generate an access control decision using vnode parameters


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

     int
     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);


DESCRIPTION
     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
     privilege 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.
     Implementations of VOP_ACCESS(9) may choose to implement additional
     security mechanisms whose results will be composed with the return value.

     The algorithm used by vaccess() selects a component of the file
     permission 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 credential 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
     compared 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.


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


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

     [EPERM]            Operation not permitted.  An attempt was made to
                        perform an operation limited to processes with
                        appropriate privileges or to the owner of a file or
                        other resource.


SEE ALSO
     vaccess_acl_posix1e(9), vnode(9), VOP_ACCESS(9)


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