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, mode_t acc_mode, struct ucred *cred, int *privused);
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 superuser
privilege, if available for the credential, will also be considered.
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 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
vaccess_acl_posix1e(9), vnode(9), VOP_ACCESS(9)
This man page and the current implementation of vaccess() were written by
FreeBSD 5.2.1 August 22, 2001 FreeBSD 5.2.1 [ Back ]