AUSCERT External Security Bulletin Redistribution
                      ESB-2000.013 -- FreeBSD-SA-00:01
                 Insecure temporary file handling in make(1)
                               21 January 2000


The FreeBSD Security Team has released the following advisory concerning a 
/tmp race condition vulnerability.  This vulnerability may allow local 
users to execute commands with the privileges of another user.

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FreeBSD-SA-00:01                                            Security Advisory
                                                                FreeBSD, Inc.

Topic:          Insecure temporary file handling in make(1)

Category:       core
Module:         make
Announced:      2000-01-19
Affects:        All versions before the correction date.
Corrected:      2000-01-16
FreeBSD only:   NO

Patches:        ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:01/make.patch

I.   Background

The make(1) program is typically used to schedule building of source
code. It has a switch ('-j') to allow parallel building by spawning
multiple child processes.

II.  Problem Description

The -j option to make(1) uses temporary files in /tmp to communicate
with its child processes by storing the shell command the child should
execute. This is useful on multi-processor architectures for making
use of all of the available CPUs, and is also widely used on
uniprocessor systems to minimize the scheduling latency of the build

However make(1) uses the temporary file in an insecure way, repeatedly
deleting and reusing the same file name for the entire life of the
program. This makes it vulnerable to a race condition wherein a
malicious user could observe the name of the temporary file being
used, and replace the contents of a later instance of the file with
her desired commands after the legitimate commands have been written.

This vulnerability was discovered as part of the FreeBSD Auditing
Project, an ongoing effort to identify and correct security
vulnerabilities in the FreeBSD operating system.

All versions of NetBSD and OpenBSD are also believed to be vulnerable
to this problem. Other systems using a BSD-derived make(1) binary may
also be vulnerable.

III. Impact

Local users could execute arbitrary shell commands as part of the
build process scheduled by "make -j" by another user.

IV.  Workaround

Avoid using the '-j' flag to make(1).

V.   Solution

Upgrade your system to one that is listed above as having the problem
resolved, or patch your present system.

To patch your present system: save the patch below into a file, and
execute the following commands as root:

cd /usr/src/usr.bin/make
patch < /path/to/patch/file
make all
make install

Patches for 3.4-STABLE and 4.0-CURRENT systems before the resolution date:

    Index: job.c
    RCS file: /home/ncvs/src/usr.bin/make/job.c,v
    retrieving revision 1.16
    diff -u -r1.16 job.c
    --- job.c	1999/09/11 13:08:01	1.16
    +++ job.c	2000/01/17 01:42:57
    @@ -163,14 +163,6 @@
     #define JOB_STOPPED	3   	/* The job is stopped */
    - * tfile is the name of a file into which all shell commands are put. It is
    - * used over by removing it before the child shell is executed. The XXXXXXXXXX
    - * in the string are replaced by mkstemp(3).
    - */
    -static char     tfile[sizeof(TMPPAT)];
      * Descriptions for various shells.
     static Shell    shells[] = {
    @@ -993,7 +985,7 @@
     	 * If we are aborting and the job table is now empty, we finish.
    -	(void) eunlink(tfile);
    +	(void) eunlink(job->tfile);
    @@ -1668,6 +1660,7 @@
         Boolean	  cmdsOK;     /* true if the nodes commands were all right */
         Boolean 	  local;      /* Set true if the job was run locally */
         Boolean 	  noExec;     /* Set true if we decide not to run the job */
    +    int		  tfd;	      /* File descriptor for temp file */
         if (previous != NULL) {
     	previous->flags &= ~(JOB_FIRST|JOB_IGNERR|JOB_SILENT|JOB_REMOTE);
    @@ -1697,6 +1690,12 @@
         job->flags |= flags;
    +    (void) strcpy(job->tfile, TMPPAT);
    +    if ((tfd = mkstemp(job->tfile)) == -1)
    +	Punt("cannot create temp file: %s", strerror(errno));
    +    else
    +	(void) close(tfd);
          * Check the commands now so any attributes from .DEFAULT have a chance
          * to migrate to the node
    @@ -1722,9 +1721,9 @@
    -	job->cmdFILE = fopen(tfile, "w+");
    +	job->cmdFILE = fopen(job->tfile, "w+");
     	if (job->cmdFILE == NULL) {
    -	    Punt("Could not open %s", tfile);
    +	    Punt("Could not open %s", job->tfile);
     	(void) fcntl(FILENO(job->cmdFILE), F_SETFD, 1);
    @@ -1830,7 +1829,7 @@
     	 * Unlink and close the command file if we opened one
     	if (job->cmdFILE != stdout) {
    -	    (void) eunlink(tfile);
    +	    (void) eunlink(job->tfile);
     	    if (job->cmdFILE != NULL)
     		(void) fclose(job->cmdFILE);
     	} else {
    @@ -1859,7 +1858,7 @@
         } else {
     	(void) fflush(job->cmdFILE);
    -	(void) eunlink(tfile);
    +	(void) eunlink(job->tfile);
    @@ -2403,13 +2402,6 @@
     			     * be running at once. */
         GNode         *begin;     /* node for commands to do at the very start */
    -    int	          tfd;
    -    (void) strcpy(tfile, TMPPAT);
    -    if ((tfd = mkstemp(tfile)) == -1)
    -	Punt("cannot create temp file: %s", strerror(errno));
    -    else
    -	(void) close(tfd);
         jobs =  	  Lst_Init(FALSE);
         stoppedJobs = Lst_Init(FALSE);
    @@ -2914,7 +2906,7 @@
    -    (void) eunlink(tfile);
    +    (void) eunlink(job->tfile);
    @@ -2948,7 +2940,6 @@
    -    (void) eunlink(tfile);
    @@ -3024,6 +3015,7 @@
     	    KILL(job->pid, SIGINT);
     	    KILL(job->pid, SIGKILL);
     #endif /* RMT_WANTS_SIGNALS */
    +	    (void) eunlink(job->tfile);
    @@ -3032,7 +3024,6 @@
         while (waitpid((pid_t) -1, &foo, WNOHANG) > 0)
    -    (void) eunlink(tfile);
     #ifdef REMOTE
    Index: job.h
    RCS file: /home/ncvs/src/usr.bin/make/job.h,v
    retrieving revision 1.10
    diff -u -r1.10 job.h
    --- job.h	1999/08/28 01:03:31	1.10
    +++ job.h	2000/01/17 01:42:31
    @@ -93,6 +93,8 @@
     #define JOB_BUFSIZE	1024
     typedef struct Job {
         int       	pid;	    /* The child's process ID */
    +    char	tfile[sizeof(TMPPAT)];
    +			    /* Temporary file to use for job */
         GNode    	*node;      /* The target the child is making */
         LstNode 	tailCmds;   /* The node of the first command to be
     			     * saved when the job has been run */
FreeBSD, Inc.

Web Site:                       http://www.freebsd.org/
Confidential contacts:          security-officer@freebsd.org
Security notifications:         security-notifications@freebsd.org
Security public discussion:     freebsd-security@freebsd.org
PGP Key:                ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc

Notice: Any patches in this document may not apply cleanly due to
        modifications caused by digital signature or mailer software.
        Please reference the URL listed at the top of this document
        for original copies of all patches if necessary.

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