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 toNULL 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.