linux-kernel - Re: [PATCH] fs: check for DAC_READ_SEARCH instead of SYS

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Date:   Sun, 22 Oct 2017 01:25:36 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Nicolas Belouin <nicolas@...ouin.fr>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] fs: check for DAC_READ_SEARCH instead of SYS_ADMIN

On Sat, Oct 21, 2017 at 03:24:46PM +0200, Nicolas Belouin wrote:
> These checks are meant to prevent leaks or attacks via directory
> traversal, the use of CAP_SYS_ADMIN here is a misuse,
> CAP_DAC_READ_SEARCH being way more appropriate as a process
> with CAP_DAC_READ_SEARCH is entrusted with going trough all directories.
> CAP_SYS_ADMIN is not meant to flag such a process.
> 
> Signed-off-by: Nicolas Belouin <nicolas@...ouin.fr>

No.  lookup_dcookie() is a horrid, horrid, hack which is
*spectacularly* dangerous.  We should not be trying to encourage its
use for anything beside its single legacy user, oprofile(8), for which
CAP_SYS_ADMIN is appropriate.

						- Ted