linux-kernel - Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY

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Message-ID: <CA+55aFzcPFXei5j-i49+3kXZ5L9S-v66vrzU091EuXkSeg1G7A@mail.gmail.com>
Date:	Mon, 26 Aug 2013 10:37:57 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Andy Lutomirski <luto@...capital.net>, Willy Tarreau <w@....eu>,
	"security@...nel.org" <security@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH)

On Sun, Aug 25, 2013 at 1:23 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So I'll just go back to square one, and wonder if we could/should just
> make the rule be that in order to be in that LAST_BIND case, you
> really have to have f_cred match your own credentials. Or have
> CAP_SEARCH.

Nope. That doesn't work. It breaks the chrome sandboxing.

Right now, following a /proc fd symlink requires ptrace access to the
process. Which is actually pretty strict, and makes sense. But it does
mean that there are other capabilities than CAP_DAC_READ_SEARCH at
play.

I'm playing with a patch that then in addition to the ptrace check
*also* requires that the file was opened with the same credentials as
the follower _or_ the task being followed. I'll see if that works out.

                Linus
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