PATCH: 4.1.0: mkstemp

PATCH: 4.1.0: mkstemp

[Peter Stephenson]

gcc has taken to complaining about using mktemp() instead of mkstemp().

Index: zshconfig.ac
===================================================================
RCS file: /cvsroot/zsh/zsh/zshconfig.ac,v
retrieving revision 1.5
diff -u -r1.5 zshconfig.ac
--- zshconfig.ac	2001/06/08 18:34:53	1.5
+++ zshconfig.ac	2001/06/15 22:10:13
@@ -915,7 +915,7 @@
 	       readlink faccessx fchdir ftruncate \
 	       fstat lstat lchown \
 	       fseeko ftello \
-	       mkfifo _mktemp \
+	       mkfifo _mktemp mkstemp \
 	       waitpid wait3 \
 	       sigaction sigblock sighold sigrelse sigsetmask sigprocmask \
 	       killpg setpgid setpgrp tcsetpgrp tcgetattr nice \
Index: Src/utils.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/utils.c,v
retrieving revision 1.33
diff -u -r1.33 utils.c
--- Src/utils.c	2001/06/09 18:06:32	1.33
+++ Src/utils.c	2001/06/15 22:10:21
@@ -1101,11 +1101,14 @@
     if (!(s = getsparam("TMPPREFIX")))
 	s = DEFAULT_TMPPREFIX;
  
+#ifdef HAVE_MKSTEMP
+    ret = ((char *) mkstemp(dyncat(unmeta(s), "XXXXXX")));
 #ifdef HAVE__MKTEMP
     /* Zsh uses mktemp() safely, so silence the warnings */
     ret = ((char *) _mktemp(dyncat(unmeta(s), "XXXXXX")));
 #else
     ret = ((char *) mktemp(dyncat(unmeta(s), "XXXXXX")));
+#endif
 #endif
     unqueue_signals();
 

-- 
Peter Stephenson <pws@pwstephenson.fsnet.co.uk>
Work: pws@csr.com
Web: http://www.pwstephenson.fsnet.co.uk

Re: PATCH: 4.1.0: mkstemp

[Wayne Davison]

On Sat, 16 Jun 2001, Peter Stephenson wrote:
> gcc has taken to complaining about using mktemp() instead of mkstemp().

Since mkstemp() returns a file handle, not a file name, I reverted the
code in util.c back to how it was.

..wayne..

Re: PATCH: 4.1.0: mkstemp

[Bart Schaefer]

On Jun 15,  4:56pm, Wayne Davison wrote:
} Subject: Re: PATCH: 4.1.0: mkstemp
}
} On Sat, 16 Jun 2001, Peter Stephenson wrote:
} > gcc has taken to complaining about using mktemp() instead of mkstemp().
} 
} Since mkstemp() returns a file handle, not a file name, I reverted the
} code in util.c back to how it was.

You should have made a ChangeLog entry, or deleted PWS's ...

We could, of course, do this:

#ifdef HAVE_MKSTEMP
    if (close(mkstemp(ret = dyncat(unmeta(s), "XXXXXX"))) < 0 ||
    	unlink(ret) < 0)
    	ret = NULL;
#else
    ...

strictly for purposes of silencing silly warnings.  However, it is the
case that zsh always uses mktemp() safely -- it always opens the file
with O_CREAT|O_EXCL after generating the name, so it'll simply fail if
someone else manages to create the name first; zsh can't be duped into
using a file owned by someone else as long as $TMPPREFIX does not refer
to an NFS filesystem (in which case even mkstemp() is not safe, as far
as I can tell).

I suppose one could conceivably use this behavior to do a crude DoS attack
on a zsh user on systems where mktemp() is predictable.  Of course, the
create/unlink trick above makes it possible to actually watch for the name
to appear and then re-create it immediately after it vanishes, which is
probably worse than if it were never created in the first place.

I was just checking through the code that uses gettempname(), and there
is only one instance where we absolutely couldn't use mkstemp() instead:
The case of wanting to create a temporary FIFO.  There we'd have to do
an unlink() before the mkfifo(), which makes mkstemp() no improvement.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Zsh: http://www.zsh.org | PHPerl Project: http://phperl.sourceforge.net   

Re: PATCH: 4.1.0: mkstemp

[Wayne Davison]

On Sat, 16 Jun 2001, Bart Schaefer wrote:
> You should have made a ChangeLog entry, or deleted PWS's ...

Thanks, I got distracted there for a moment.  I've committed my
ChangeLog entry.

>     if (close(mkstemp(ret = dyncat(unmeta(s), "XXXXXX"))) < 0 ||
>     	unlink(ret) < 0)

Oooh, slimey!  That would sure silence the (dubious) warning, but I
would hate the extra open/close/unlink.  Perhaps we should just link in
a work-alike mktemp() function that doesn't generate a warning?

..wayne..

Re: PATCH: 4.1.0: mkstemp

[Geoff Wing]

Wayne Davison <wayned@users.sourceforge.net> typed:
: On Sat, 16 Jun 2001, Peter Stephenson wrote:
:> gcc has taken to complaining about using mktemp() instead of mkstemp().
: Since mkstemp() returns a file handle, not a file name, I reverted the
: code in util.c back to how it was.

Of course, given it's just about certain to be immediately clobbered by
the following lines . . . .
Peter did that around 10pm on a Friday night; he must have just come
back from the pub.  Oops :-)

....
+#ifdef HAVE_MKSTEMP
+    ret = ((char *) mkstemp(dyncat(unmeta(s), "XXXXXX")));
 #ifdef HAVE__MKTEMP
     /* Zsh uses mktemp() safely, so silence the warnings */
     ret = ((char *) _mktemp(dyncat(unmeta(s), "XXXXXX")));
 #else
     ret = ((char *) mktemp(dyncat(unmeta(s), "XXXXXX")));
+#endif
 #endif
     unqueue_signals();
....

Regards,
-- 
Geoff Wing : <gcw@pobox.com>
Rxvt Stuff : <gcw@rxvt.org>
Zsh Stuff  : <gcw@zsh.org>