vaccess

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

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.

BSD                              August 22, 2001                             BSD