From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D745A1CD32; Tue, 21 May 2024 14:45:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716302758; cv=none; b=QmBUV0aTegrohR1HT1attII7UZ8UB5s6XIElBwpaOd3V9UUhFTeoYZQ321ekjtC7xI+pz4MFLmW/HG+qpUraoPhBVeCpzBZT2ojx4ls0YR2x9SW7o0KAOOeK+nzYlHpPMHgaRviy8RL1a05ij1pIb7B3yq/suuKmQnRwMIMMo/c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716302758; c=relaxed/simple; bh=h56f1QL3jb+GHUV4CymHSyb4E4n54peG+Qn4CsaG9Ts=; h=Mime-Version:Content-Type:Date:Message-Id:Subject:From:To:Cc: References:In-Reply-To; b=hovhlnMbpxvTx4NgzMVrZQ3SCV4qBpfVBf2tXmDCJwf8JzQ3kvdS7dx+IXDxqvIUGur0mVTjreDKyJ73yfHLnSx49FUom3X85xXj/L593Qw9S7zytKIy9qOCVBpIJsTQYpEXKJiZ/RI7g64wu8DkK7Z1bndUi5wrzVCPuaySw4M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bTfMZ3+n; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bTfMZ3+n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 186EFC2BD11; Tue, 21 May 2024 14:45:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1716302757; bh=h56f1QL3jb+GHUV4CymHSyb4E4n54peG+Qn4CsaG9Ts=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=bTfMZ3+ncJE7OLdODIqNXZ6D9GrNsCumq/EQpRt77Z9Zv7L06eor07wgeqfv89scD Uu5zX7o+SWFtkq9wHB9lE/UtUdRmwKpQBgwRnvvp2cHsqRR8vyS2nNzlR1KKKnWhLp 8bBJbDfB1DCxyn5/IIE7YnJq/C6naem9KgEpliUFexiziI0pbrWlMRHmeziBo4ys97 8TadNnKqkHCElBZv7jUzucCHAqq2gyM3nonTLdTBj0hKRr34OgEyAkBVe01MumVDa8 Q2k7oOBbEXFe5GZyAZnviDypZ41Kw/7IZhkms94HsIXqgAiMA3oqJQfIWDASrPv1zd qFAIt4azUjK/A== Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 21 May 2024 17:45:52 +0300 Message-Id: Subject: Re: [PATCH 3/3] capabilities: add cap userns sysctl mask From: "Jarkko Sakkinen" To: "Tycho Andersen" Cc: "Jonathan Calmels" , , , "Luis Chamberlain" , "Kees Cook" , "Joel Granados" , "Serge Hallyn" , "Paul Moore" , "James Morris" , "David Howells" , , , , , X-Mailer: aerc 0.17.0 References: <20240516092213.6799-1-jcalmels@3xx0.net> <20240516092213.6799-4-jcalmels@3xx0.net> In-Reply-To: On Tue May 21, 2024 at 5:29 PM EEST, Tycho Andersen wrote: > On Tue, May 21, 2024 at 01:12:57AM +0300, Jarkko Sakkinen wrote: > > On Tue May 21, 2024 at 12:13 AM EEST, Tycho Andersen wrote: > > > On Mon, May 20, 2024 at 12:25:27PM -0700, Jonathan Calmels wrote: > > > > On Mon, May 20, 2024 at 07:30:14AM GMT, Tycho Andersen wrote: > > > > > there is an ongoing effort (started at [0]) to constify the first= arg > > > > > here, since you're not supposed to write to it. Your usage looks > > > > > correct to me, so I think all it needs is a literal "const" here. > > > >=20 > > > > Will do, along with the suggestions from Jarkko > > > >=20 > > > > > > + struct ctl_table t; > > > > > > + unsigned long mask_array[2]; > > > > > > + kernel_cap_t new_mask, *mask; > > > > > > + int err; > > > > > > + > > > > > > + if (write && (!capable(CAP_SETPCAP) || > > > > > > + !capable(CAP_SYS_ADMIN))) > > > > > > + return -EPERM; > > > > >=20 > > > > > ...why CAP_SYS_ADMIN? You mention it in the changelog, but don't > > > > > explain why. > > > >=20 > > > > No reason really, I was hoping we could decide what we want here. > > > > UMH uses CAP_SYS_MODULE, Serge mentioned adding a new cap maybe. > > > > > > I don't have a strong preference between SETPCAP and a new capability= , > > > but I do think it should be just one. SYS_ADMIN is already god mode > > > enough, IMO. > >=20 > > Sometimes I think would it make more sense to invent something > > completely new like capabilities but more modern and robust, instead of > > increasing complexity of a broken mechanism (especially thanks to > > CAP_MAC_ADMIN). > >=20 > > I kind of liked the idea of privilege tokens both in Symbian and Maemo > > (have been involved professionally in both). Emphasis on the idea not > > necessarily on implementation. > >=20 > > Not an LSM but like something that you could use in the place of POSIX > > caps. Probably quite tedious effort tho because you would need to pull > > the whole industry with the new thing... > > And then we have LSM hooks, (ns_)capable(), __secure_computing() plus > a new set of hooks for this new thing sprinkled around. I guess > kernel developers wouldn't be excited about it, let alone the rest of > the industry :) > > Thinking out loud: I wonder if fixing the seccomp TOCTOU against > pointers would help here. I guess you'd still have issues where your > policy engine resolves a path arg to open() and that inode changes > between the decision and the actual vfs access, you have just changed > the TOCTOU. > > Or even scarier: what if you could change the return value at any > kprobe? :) I had one crazy idea related to seccomp filters once. What if there was way to compose tokens that would be just a seccomp filter like the one that you pass to PR_SET_SECCOMP but presented with a file descriptor? Then you could send these with SCM_RIGHTS to other processes and they could upgrade their existing filter with them. So it would be a kind of extension mechanism for a seccomp filter. Not something I'm seriously suggesting but though to flush this out now that we are on these topics anyhow ;-) > Tycho PS. Sorry if my language was a bit harsh earlier but I think I had also a point related to at least to the patch set presentation. I.e. you are very precise describing the mechanism but motivation and bringing topic somehow to a context is equally important :-) BR, Jarkko