Path: utzoo!attcan!uunet!lll-winken!lll-lcc!pyramid!thirdi!peter
From: peter@thirdi.UUCP (Peter Rowell)
Newsgroups: comp.unix.wizards
Subject: Down in the Dumps (a true story)
Summary: dump can dump on *you*!
Keywords: dump, massive destruction
Message-ID: <406@thirdi.UUCP>
Date: 19 May 88 22:13:13 GMT
Reply-To: peter@thirdi.UUCP (Peter Rowell)
Organization: Third Eye Software, Menlo Park, CA
Lines: 53


If the following command does not look Evil to you, then read on....

	dump 0usf /dev/rmt0 /dev/rrf0g

I post this to the net in the hopes it will save someone else from
nailing themselves to the cross like I did.  I am sure that more than
a few people will read this and say.

    "Oh sure, *I* knew that's what would happen.  Why didn't you:
	(a) RTFM (read the friendly manual) (b) be more careful."

Well, actually, I *did* just RTFM and then I made one simple little
error and Murphy stepped all over my file system.

In case you haven't already figured it out, the command in
question (dump 0usf /dev/rmt0 /dev/rrf0g) will wipe out the
file system residing on device /dev/rrf0g! (Yes, it really did...)

The problem is that the "s" flag is looking for a size specification for
the tape (which I accidently left out).  It apparently ate "/dev/rmt0"
and decided that it liked that just fine.  Next, the "f" flag says "Oh
boy! I get to do the dump TO /dev/rrf0g".  Now, it would have been nice
if dump had complained that I had not told it what device to dump FROM,
but Nnnoooooo, the manual says:

     " ... If no arguments are given, the key is assumed to be 9u and a
     default file system is dumped to the default tape.  ..."
     ^^^^^^^^^^^^^^^^^^^
The default on my system (an ISI box running 4.3) is /dev/rsd0g.  Since
this is a valid device on my system, dump promptly started dumping /usr
all over rrf0fg.

I saw right away that I had left the length off and interrupted the dump.
When I started it up again (with the length) it informed me that the
super-block was now caca and that I should run fsck with the -b switch.
I did this with -b 32 and -b 11600 and -b etc. etc. etc. sigh.
(Through no fault of my own, we did have a recent dump to restore from.)

In conclusion:
I *know* that being root is dangerous.  I just never expected that
I could *create* a dead file system by using dump!

I personally would like to see dump modified along these lines:

	1.	Not default *anything* (except, perhaps, dump TO tape).
	2.	Be pickier about what a valid numerical value is.
	3.	Require confirmation for dangerous target devices.
		(Such as mounted file systems or things in /etc/fstab.)

--------------------------------------------------------------------------
Peter Rowell					"He's dead, Jim."
Third Eye Software, Inc.			...!pyramid!thirdi!peter
(415) 321-0967