Subject: Re: bug#32772: TOCTOU bug in chmod

From: Paul Eggert <[email-masked]>
Date: Wed, 19 Sep 2018 12:56:59 -0700

Jeff Epler wrote:
> Changing to lchmodat should resolve the problem

No, that would just introduce the opposite bug: chmod is supposed to follow a 
symlink, and using lchmod would let an attacker provoke a race that would cause 
chmod to not follow a symlink that it should.

A better way to fix this problem on GNU/Linux is to use O_PATH, not lchmod. I 
don't know of any way to fix it on other platforms that lack O_PATH.