Re: Hard link creation witout write access

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> It seems to me the rule should be:

> 1. If you own the file you can make hard links.
> 2. If you are in the file's group and the file is group-writable you
>    can make hard links.
> 3. Maybe if the file is other-writable you can make hard links.

> The problem with sort in /tmp is that hardlink_check_gid requires you
> to be in the file's group _even if you own the file_, which is also a
> bonkers restriction.

I concur with that last.  But note that ordinary file permissions will
do some apparently-bonkers things, like

% echo foo > z3
% chmod 044 z3
% cat z3
cat: z3: Permission denied
% 
# chown 0 z3		<-- note prompt, done as root
% cat z3
foo
% 

I can't read the file when I own it even though anyone _not_ owning it
can read it just fine.  Similarly, if the file is mode 004 and I'm in
its group, I can't read it even though anyone neither owner nor in its
group can lread it.

Is that bonkers?  Some people would probably say so.  I don't; I
consider "fixing" that "problem" to be a case of forbidding stupid
things and thereby forbidding clever things.

But then, I'm not convinced this is a real hazard.  "ln /etc/motd
/var/mail/mouse" and sending mail - the problem there exists only if
the mailer is stupid enough to open /var/mail/mouse as someone other
than mouse; if it's a real issue, it's a bug in the mailer, not a
problem with hardlinks.  You get the same issue with a symlink if the
mailer is willing to deliver to a symlink.

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