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 creden

tial 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_AC

CESS(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 nei

ther 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 cre

dential. If the
rights granted by discretionary protections are insuffi

cient, then superuser privilege, if available for the credential, will also

be considered.

RETURN VALUES

vaccess() will return 0 on success, or a non-zero error val

ue on failure.

ERRORS

[EACCES] Permission denied. An attempt was made

to access a

file in a way forbidden by its file ac

cess permissions.

[EPERM] Operation not permitted. An attempt was

made to per

form 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