Subject: bug#51327: 28.0.60; emacsclient warns about XDG_RUNTIME_DIR when starting daemon on-demand

From: Paul Eggert <[email-masked]>
Date: Tue, 7 Dec 2021 11:03:35 -0800

On 12/7/21 06:58, Stefan Kangas wrote:
> Eli Zaretskii <[email-masked]> writes:
> 
>>> Agreed.  The only question is if this patch should go to emacs-28 or
>>> master?  Perhaps Eli or Lars has an opinion about that.
>>
>> AFAIU, Ulrich wasn't happy with that patch and proposed an
>> alternative?
> 
> You are correct, so it seems like we need to think about this more
> closely before taking action.
> 
> I linked the relevant emacs-devel thread with more discussion
> separately.

Although none of us has done a thorough security audit, I still think 
that looking in TMPDIR first is a security loophole that is exploitable 
in some circumstances.

Ulrich says the loophole is small because Emacs verifies that the 
current user is the socket owner. However, small loopholes can still be 
exploited: for example, an attacker could cause you to think that you're 
connecting to your Emacs when you're really connecting to another of 
your processes, and this could still lead to problems (particularly if 
you're root).