128 lines
4.3 KiB
Groff
128 lines
4.3 KiB
Groff
.\"-
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.\" Copyright (c) 2001 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 22, 2001
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.Os
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.Dt VACCESS 9
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.Sh NAME
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.Nm vaccess
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.Nd generate an access control decision using vnode parameters
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/vnode.h
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.Ft int
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.Fo vaccess
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.Fa "enum vtype type"
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.Fa "mode_t file_mode"
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.Fa "uid_t file_uid"
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.Fa "gid_t file_gid"
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.Fa "mode_t acc_mode"
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.Fa "struct ucred *cred"
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.Fa "int *privused"
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.Fc
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.Sh DESCRIPTION
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This call implements the logic for the
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.Ux
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discretionary file security model
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common to many file systems in
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.Fx .
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It accepts the vnodes type
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.Fa type ,
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permissions via
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.Fa file_mode ,
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owning UID
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.Fa file_uid ,
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owning GID
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.Fa file_gid ,
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desired access mode
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.Fa acc_mode ,
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requesting credential
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.Fa cred ,
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and an optional call-by-reference
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.Vt int
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pointer returning whether or not
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privilege was required for successful evaluation of the call; the
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.Fa privused
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pointer may be set to
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.Dv NULL
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by the caller in order not to be informed of
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privilege information, or it may point to an integer that will be set to
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1 if privilege is used, and 0 otherwise.
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.Pp
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This call is intended to support implementations of
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.Xr VOP_ACCESS 9 ,
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which will use their own access methods to retrieve the vnode properties,
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and then invoke
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.Fn vaccess
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in order to perform the actual check.
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Implementations of
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.Xr VOP_ACCESS 9
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may choose to implement additional security mechanisms whose results will
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be composed with the return value.
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.Pp
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The algorithm used by
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.Fn vaccess
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selects a component of the file permission bits based on comparing the
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passed credential, file owner, and file group.
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If the credential's effective UID matches the file owner, then the
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owner component of the permission bits is selected.
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If the UID does not match, then the credential's effective GID, followed
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by additional groups, are compared with the file group\[em]if there is
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a match, then the group component of the permission bits is selected.
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If neither the credential UID or GIDs match the passed file owner and
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group, then the other component of the permission bits is selected.
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.Pp
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Once appropriate protections are selected for the current credential,
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the requested access mode, in combination with the vnode type, will be
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compared with the discretionary rights available for the credential.
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If the rights granted by discretionary protections are insufficient,
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then super-user privilege, if available for the credential, will also be
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considered.
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.Sh RETURN VALUES
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.Fn vaccess
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will return 0 on success, or a non-zero error value on failure.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EACCES
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Permission denied.
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An attempt was made to access a file in a way forbidden by its file access
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permissions.
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.It Bq Er EPERM
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Operation not permitted.
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An attempt was made to perform an operation limited to processes with
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appropriate privileges or to the owner of a file or other resource.
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.El
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.Sh SEE ALSO
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.Xr vaccess_acl_posix1e 9 ,
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.Xr vnode 9 ,
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.Xr VOP_ACCESS 9
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.Sh AUTHORS
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This manual page and the current implementation of
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.Fn vaccess
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were written by
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.An Robert Watson .
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