| VACCESS(9) | Kernel Developer's Manual | VACCESS(9) |
vaccess — generate
an access control decision using vnode parameters
#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);
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 considered.
vaccess() will return 0 on success, or a
non-zero error value on failure.
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.
| September 18, 2009 | Debian |