256 lines
6.3 KiB
Groff
256 lines
6.3 KiB
Groff
.\" 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.
|
|
.\"
|
|
.\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd February 11, 1998
|
|
.Dt MKTEMP 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mktemp
|
|
.Nd make temporary file name (unique)
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In unistd.h
|
|
.Ft char *
|
|
.Fn mktemp "char *template"
|
|
.Ft int
|
|
.Fn mkstemp "char *template"
|
|
.Ft int
|
|
.Fn mkstemps "char *template" "int suffixlen"
|
|
.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 guaranteed not to exist at the time of function invocation
|
|
and is 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.XXXXXX .
|
|
The trailing
|
|
.Ql X Ns s
|
|
are replaced with a
|
|
unique alphanumeric 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
|
|
selecting one of 56800235584 (62 ** 6) possible temporary file names.
|
|
.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 mkstemps
|
|
function acts the same as
|
|
.Fn mkstemp ,
|
|
except it permits a suffix to exist in the template.
|
|
The template should be of the form
|
|
.Pa /tmp/tmpXXXXXXsuffix .
|
|
The
|
|
.Fn mkstemps
|
|
function
|
|
is told the length of the suffix string.
|
|
.Pp
|
|
The
|
|
.Fn mkdtemp
|
|
function makes the same replacement to the template as in
|
|
.Fn mktemp
|
|
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
|
|
and
|
|
.Fn mkstemps
|
|
functions
|
|
return \-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 ,
|
|
.Fn mkstemps
|
|
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 ,
|
|
.Fn mkstemps
|
|
and
|
|
.Fn mkdtemp
|
|
functions
|
|
may also set
|
|
.Va errno
|
|
to any value specified by the
|
|
.Xr stat 2
|
|
function.
|
|
.Pp
|
|
The
|
|
.Fn mkstemp
|
|
and
|
|
.Fn mkstemps
|
|
functions
|
|
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 NOTES
|
|
A common problem that results in a core dump is that the programmer
|
|
passes in a read-only string to
|
|
.Fn mktemp ,
|
|
.Fn mkstemp ,
|
|
.Fn mkstemps
|
|
or
|
|
.Fn mkdtemp .
|
|
This is common with programs that were developed before
|
|
.St -isoC
|
|
compilers were common.
|
|
For example, calling
|
|
.Fn mkstemp
|
|
with an argument of
|
|
.Qq /tmp/tempfile.XXXXXX
|
|
will result in a core dump due to
|
|
.Fn mkstemp
|
|
attempting to modify the string constant that was given.
|
|
If the program in question makes heavy use of that type
|
|
of function call, you do have the option of compiling the program
|
|
so that it will store string constants in a writable segment of memory.
|
|
See
|
|
.Xr gcc 1
|
|
for more information.
|
|
.Sh SEE ALSO
|
|
.Xr chmod 2 ,
|
|
.Xr getpid 2 ,
|
|
.Xr mkdir 2 ,
|
|
.Xr open 2 ,
|
|
.Xr stat 2
|
|
.Sh HISTORY
|
|
A
|
|
.Fn mktemp
|
|
function appeared in
|
|
.At v7 .
|
|
The
|
|
.Fn mkstemp
|
|
function appeared in
|
|
.Bx 4.4 .
|
|
The
|
|
.Fn mkdtemp
|
|
function first appeared in
|
|
.Ox 2.2 ,
|
|
and later in
|
|
.Fx 3.2 .
|
|
The
|
|
.Fn mkstemps
|
|
function first appeared in
|
|
.Ox 2.4 ,
|
|
and later in
|
|
.Fx 3.4 .
|
|
.Sh BUGS
|
|
This family of functions produces filenames which can be guessed,
|
|
though the risk is minimized when large numbers of
|
|
.Ql X Ns s
|
|
are used to
|
|
increase the number of possible temporary filenames.
|
|
This makes the race in
|
|
.Fn mktemp ,
|
|
between testing for a file's existence (in the
|
|
.Fn mktemp
|
|
function call)
|
|
and opening it for use
|
|
(later in the user application)
|
|
particularly dangerous from a security perspective.
|
|
Whenever it is possible,
|
|
.Fn mkstemp
|
|
should be used instead, since it does not have the race condition.
|
|
If
|
|
.Fn mkstemp
|
|
cannot be used, the filename created by
|
|
.Fn mktemp
|
|
should be created using the
|
|
.Dv O_EXCL
|
|
flag to
|
|
.Xr open 2
|
|
and the return status of the call should be tested for failure.
|
|
This will ensure that the program does not continue blindly
|
|
in the event that an attacker has already created the file
|
|
with the intention of manipulating or reading its contents.
|
|
.Pp
|
|
The implementation of these functions calls
|
|
.Xr arc4random 3 ,
|
|
which is not reentrant.
|
|
You must provide your own locking around this and other consumers of the
|
|
.Xr arc4random 3
|
|
API.
|