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VACCESS(9)             FreeBSD Kernel Developer's Manual            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 credential cred, and
     an optional call-by-reference int pointer returning whether or not privi-
     lege 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.  Implementa-
     tions of VOP_ACCESS(9) may choose to implement additional security mecha-
     nisms whose results will be composed with the return value.

     The algorithm used by vaccess() selects a component of the file permis-
     sion 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 cre-
     dential 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 com-
     pared 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 permis-
                        sions.

     [EPERM]            Operation not permitted.  An attempt was made to per-
                        form an operation limited to processes with appropri-
                        ate 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.

FreeBSD 6.2                     August 22, 2001                    FreeBSD 6.2

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | AUTHORS

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