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,    accmode_t accmode,
           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 accmode, 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_nfs4(9), vaccess_acl_posix1e(9), vnode(9), VOP_ACCESS(9)

AUTHORS

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

Debian                                         September 18, 2009                                     VACCESS(9)