linux-kernel - Re: [RFC PATCH 1/2] security, capabilities: create CAP

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Message-Id: <201710211909.v9LJ9Zg8033866@smtp6.infomaniak.ch>
Date:   Sat, 21 Oct 2017 21:09:32 +0200
From:   nicolas@...ouin.fr
To:     "Serge E. Hallyn" <serge@...lyn.com>
CC:     Jan Kara <jack@...e.com>, "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Dave Kleikamp <shaggy@...nel.org>,
        Mark Fasheh <mfasheh@...sity.com>,
        Joel Becker <jlbec@...lplan.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Phillip Lougher <phillip@...ashfs.org.uk>,
        Richard Weinberger <richard@....at>,
        Artem Bityutskiy <dedekind1@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Serge Hallyn <serge@...lyn.com>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        James.Morris@...p6.infomaniak.ch
Subject: Re: [RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

<james.l.morris@...cle.com>,linux-ext4@...r.kernel.org,linux-kernel@...r.kernel.org,linux-f2fs-devel@...ts.sourceforge.net,linux-fsdevel@...r.kernel.org,linux-mtd@...ts.infradead.org,jfs-discussion@...ts.sourceforge.net,ocfs2-devel@....oracle.com,linux-unionfs@...r.kernel.org,reiserfs-devel@...r.kernel.org,linux-security-module@...r.kernel.org,selinux@...ho.nsa.gov,linux-api@...r.kernel.org,kernel-hardening@...ts.openwall.com
From: Nicolas Belouin <nicolas@...ouin.fr>
Message-ID: <99179B10-4EAE-4FAB-9D14-B885156261B3@...ouin.fr>



On October 21, 2017 6:03:02 PM GMT+02:00, "Serge E. Hallyn" <serge@...lyn.com> wrote:
>Quoting Nicolas Belouin (nicolas@...ouin.fr):
>> with CAP_SYS_ADMIN being bloated, the usefulness of using it to
>> flag a process to be entrusted for e.g reading and writing trusted
>> xattr is near zero.
>> CAP_TRUSTED aims to provide userland with a way to mark a process as
>> entrusted to do specific (not specially admin-centered) actions. It
>> would for example allow a process to red/write the trusted xattrs.
>
>You say "for example".  Are you intending to add more uses?  If so,
>what
>are they?  If not, how about renaming it CAP_TRUSTED_XATTR?
>

I don't see any other use for now, but I don't want it to be too narrow and non usable in a similar context in the future. So I believe the underlying purpose of marking a process as "trusted" (even if for now it only means rw permission on trusted xattr) is more meaningful.

>What all does allowing writes to trusted xattrs give you?  There are
>the overlayfs whiteouts, what else?

Nicolas