generate an access control decision using vnode parameters
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
vaccess(enum vtype type,
mode_t file_mode, uid_t
file_uid, gid_t file_gid,
accmode_t accmode, struct ucred
*cred, int *privused);
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
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
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.
This manual page and the current implementation of
- Permission denied. An attempt was made to access a file in a way forbidden
by its file access permissions.
- 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.
vaccess() were written by Robert