linux-kernel - Re: [PATCH v6 1/1] ns: add binfmt

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Date:   Tue, 6 Nov 2018 20:40:57 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Laurent Vivier <laurent@...ier.eu>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrei Vagin <avagin@...il.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        containers@...ts.linux-foundation.org, dima@...sta.com
Subject: Re: [PATCH v6 1/1] ns: add binfmt_misc to the user namespace

On Tue, Oct 30, 2018 at 9:51 AM Laurent Vivier <laurent@...ier.eu> wrote:
> Le 24/10/2018 à 19:15, Laurent Vivier a écrit :
> > On 16/10/2018 17:22, Andrei Vagin wrote:
> >> On Wed, Oct 10, 2018 at 06:14:30PM +0200, Laurent Vivier wrote:
> >>> This patch allows to have a different binfmt_misc configuration
> >>> for each new user namespace. By default, the binfmt_misc configuration
> >>> is the one of the previous level, but if the binfmt_misc filesystem is
> >>> mounted in the new namespace a new empty binfmt instance is created and
> >>> used in this namespace.
> >>>
> >>> For instance, using "unshare" we can start a chroot of another
> >>> architecture and configure the binfmt_misc interpreter without being root
> >>> to run the binaries in this chroot.
> >>>
> >>> Signed-off-by: Laurent Vivier <laurent@...ier.eu>
> >>
> >> Acked-by: Andrei Vagin <avagin@...il.com>
> >>
> >> Thanks,
> >> Andrei
> >>
> >
> > I don't konw who is the maintainer for this part,

I think Andrew Morton is the right maintainer here.

> > but is there any
> > chance to have this merged in 4.20?
> >
>
> I'd really want to have this merged.
>
> I have some real use cases for this:
>
> 1- to allow a non root user to run a container (with "unshare" for
> instance) with its own binfmt_misc configuration. For instance, like we
> provide a disk image and ask an ordinary user to run it with his
> favorite VM hypervisor, we can provide a tar.gz containing our own
> interpreter and just ask him to unshare+chroot to the exploded file tree,
>
> 2- to allow to run automatic tests of an interpreter on a machine
> without having to change the global configuration of the system. I have
> in mind to add some tests in Avocado to automatically test
> qemu-linux-user in containers, so the interpreter path can depend on the
> build path and possibly run them concurrently,
>
> 3- to select an interpreter by container. For instance, on the
> qemu-devel mailing list, we have a waiting patch to add the bFLT
> interpreter binfmt_misc configuration, but the bFLT doesn't provide the
> CPU type in magic/mask. So it would be interesting to be able to select
> also a bFLT interpreter by container, as we know the CPU architecture we
> have in each chroot/container,
>
> 4- another example to select an interpreter by container is qemu-mips
> and qemu-misn32 share the same magic/mask because only the kernel API
> changes, so we can't configure both on the system (but I agree it's a
> QEMU bug: they should be merged and the kernel API be selected at runtime).