Date: Sat, 2 Feb 2002 07:10:02 -0800 (PST)
From: Peter Pentchev <roam@ringlet.net>
To: freebsd-bugs@FreeBSD.org
Subject: Re: bin/34483: wrong execv() call in amd for ${mount} and ${unmount} if mount type:=program in amd.map
Message-ID: <200202021510.g12FA2n72257@freefall.freebsd.org>
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The following reply was made to PR bin/34483; it has been noted by GNATS.
From: Peter Pentchev <roam@ringlet.net>
To: Artem 'Zazoobr' Ignatjev <timon@memphis.mephi.ru>
Cc: bug-followup@FreeBSD.org
Subject: Re: bin/34483: wrong execv() call in amd for ${mount} and ${unmount} if mount type:=program in amd.map
Date: Sat, 2 Feb 2002 17:00:18 +0200
On Sat, Feb 02, 2002 at 02:40:02AM -0800, Artem 'Zazoobr' Ignatjev wrote:
> Hi.
> Here is reply from author, Erez Zadok (from amd-dev <amd-dev@cs.columbia.edu> mailing list):
>
[snip]
> > type:=program;mount:="/etc/mount mount /this /here"
[snip]
> > It's a
> > source of unfortunate confusion to programmers who are used to think that
> > it's just an argv[] list. It's not.
>
> But I still think, that in case of hardlinks, this patch will work, and all man have to do
> is to write the correct path in map; in other cases there could be no possibility to mount
> filesystem "by hands", without writing shell script/tiny program, which will call exec...() on
> one path, giving argv[0] with other prog's name.
Actually, I now believe Erez to be correct - I no longer think this is a bug.
What he is trying to say is that you should provide argv[0] along with
the other arguments, *after* the path to the program. This allows you
to execute a program, giving it an argv[0] different from the filename
of the executable file - exactly the same way that inetd.conf's syntax
allows you to do the same. This is done to minimize the need for
hardlinks, as you say; even without a hardlink, you are able to invoke,
say, /sbin/mount as either 'mount' or 'mount_ffs' or 'mount_msdosfs' or
whatever else you like.
Just take a look at inetd.conf: it will illustrate this perfectly:
ftp stream tcp nowait root /usr/libexec/ftpd ftpd -l
This is equivalent to amd's syntax of:
type:=program;mount:="/usr/libexec/ftpd ftpd -l"
IOW, invoke the program executable file /usr/libexec/ftpd, and pass
it an argv[] list of argv[0]="ftpd", argv[1]="-l", argv[2]=NULL.
If you do not wish to invoke programs with names other than their
executable files' names, you just have to provide the program name
twice, as in:
type:=program;mount:="mount mount blah"
..though this is both unusable and insecure (think PATH). In an ideal
case, you would provide a full path to the executable and just a name
for the program, as in:
type:=program;mount:="/sbin/mount mount blah"
Can you provide an example of an executable/program name, which can NOT
be handled by this scheme? If not, I think this PR should be closed..
Still, thanks for your effort to improve FreeBSD by filing a report on
what you believed was a genuine problem!
G'luck,
Peter
--
Peter Pentchev roam@ringlet.net roam@FreeBSD.org
Hey, out there - is it *you* reading me, or is it someone else?
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