GNU bug report logs - #32772
chmod: use O_PATH to avoid TOCTOU bug

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Message #11 received at 32772 <at> debbugs.gnu.org (full text, mbox):

From: Jeff Epler <jepler <at> gmail.com>
To: eggert <at> cs.ucla.edu
Cc: 32772 <at> debbugs.gnu.org
Subject: Re: bug#32772: TOCTOU bug in chmod
Date: Wed, 19 Sep 2018 19:47:57 -0500

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Thanks for the correction, I should have not suggested a fix off the top of
my head.

On Wed, Sep 19, 2018 at 2:57 PM Paul Eggert <eggert <at> cs.ucla.edu> wrote:

> 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.
>

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