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.\" $OpenBSD: mktemp.3,v 1.10 1998/03/16 22:32:31 deraadt Exp $
.\"
.\" Copyright (c) 1989, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd June 4, 1993
.Dt MKTEMP 3
.Os
.Sh NAME
.Nm mktemp
.Nd make temporary file name (unique)
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft char *
.Fn mktemp "char *template"
.Ft int
.Fn mkstemp "char *template"
.Ft char *
.Fn mkdtemp "char *template"
.Sh DESCRIPTION
The
.Fn mktemp
function
takes the given file name template and overwrites a portion of it
to create a file name.
This file name is unique and suitable for use
by the application.
The template may be any file name with some number of
.Ql X Ns s
appended
to it, for example
.Pa /tmp/temp.XXXX .
The trailing
.Ql X Ns s
are replaced with the current process number and/or a
unique letter combination.
The number of unique file names
.Fn mktemp
can return depends on the number of
.Ql X Ns s
provided; six
.Ql X Ns s
will
result in
.Fn mktemp
testing roughly 26 ** 6 combinations.
At least 6
.Ql X Ns s
should be used, though 10 is much better.
.Pp
The
.Fn mkstemp
function
makes the same replacement to the template and creates the template file,
mode 0600, returning a file descriptor opened for reading and writing.
This avoids the race between testing for a file's existence and opening it
for use.
.Pp
The
.Fn mkdtemp
function makes the same replacement to the template as in
.Xr mktemp 3
and creates the template directory, mode 0700.
.Sh RETURN VALUES
The
.Fn mktemp
and
.Fn mkdtemp
functions return a pointer to the template on success and
.Dv NULL
on failure.
The
.Fn mkstemp
function
returns \-1 if no suitable file could be created.
If either call fails an error code is placed in the global variable
.Va errno .
.Sh ERRORS
The
.Fn mkstemp
and
.Fn mkdtemp
functions
may set
.Va errno
to one of the following values:
.Bl -tag -width Er
.It Bq Er ENOTDIR
The pathname portion of the template is not an existing directory.
.El
.Pp
The
.Fn mkstemp
and
.Fn mkdtemp
functions
may also set
.Va errno
to any value specified by the
.Xr stat 2
function.
.Pp
The
.Fn mkstemp
function
may also set
.Va errno
to any value specified by the
.Xr open 2
function.
.Pp
The
.Fn mkdtemp
function
may also set
.Va errno
to any value specified by the
.Xr mkdir 2
function.
.Sh BUGS
For
.Fn mktemp
there is an obvious race between file name selection and file
creation and deletion: the program is typically written to call
.Xr tmpnam 3 ,
.Xr tempnam 3 , or Ns
.Fn mktemp .
Subsequently, the program calls
.Xr open 2
or
.Xr fopen 3
and erroneously opens a file (or symbolic link, fifo or other
device) that the attacker has created in the expected file location.
Hence
.Fn mkstemp
is recommended, since it atomically creates the file.
An attacker can guess the filenames produced by
.Fn mktemp .
Whenever it is possible,
.Fn mkstemp
or
.Fn mkdtemp
should be used instead.
.Pp
For this reason,
.Xr ld 8
will output a warning message whenever it links code that uses the
.Fn mktemp .
.Pp
The
.Fn mkdtemp
function is nonstandard and should not be used if portability
is required.
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr getpid 2 ,
.Xr mkdir 2 ,
.Xr open 2 ,
.Xr stat 2 ,
.Xr tmpfile 3 ,
.Xr tmpnam 3 ,
.Xr tempnam 3
.Sh HISTORY
A
.Fn mktemp
function appeared in
.At v7 .
.br
The
.Fn mkdtemp
function appeared in
.Ox 2.2 .
|
