vaccess — generate an access control decision using vnode parameters
vaccess(enum vtype type, mode_t file_mode, uid_t file_uid,
gid_t file_gid, accmode_t accmode, struct ucred *cred,
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
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
[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
vaccess_acl_nfs4(9), vaccess_acl_posix1e(9), vnode(9), VOP_ACCESS(9)
This manual page and the current implementation of vaccess() were written
by Robert Watson.