table of contents
VACCESS(9) | Kernel Developer's Manual | VACCESS(9) |
NAME¶
vaccess — generate an access control decision using vnode parametersSYNOPSIS¶
#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.September 18, 2009 | Debian |