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SubjectRe: [PATCH v6 0/1] ns: introduce binfmt_misc namespace
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Date
Hi,

Any comment on this last version?

Any chance to be merged?

Thanks,
Laurent

Le 10/10/2018 à 18:14, Laurent Vivier a écrit :
> v6: Return &init_binfmt_ns instead of NULL in binfmt_ns()
> This should never happen, but to stay safe return a
> value we can use.
> change subject from "RFC" to "PATCH"
>
> v5: Use READ_ONCE()/WRITE_ONCE()
> move mount pointer struct init to bm_fill_super() and add smp_wmb()
> remove useless NULL value init
> add WARN_ON_ONCE()
>
> v4: first user namespace is initialized with &init_binfmt_ns,
> all new user namespaces are initialized with a NULL and use
> the one of the first parent that is not NULL. The pointer
> is initialized to a valid value the first time the binfmt_misc
> fs is mounted in the current user namespace.
> This allows to not change the way it was working before:
> new ns inherits values from its parent, and if parent value is modified
> (or parent creates its own binfmt entry by mounting the fs) child
> inherits it (unless it has itself mounted the fs).
>
> v3: create a structure to store binfmt_misc data,
> add a pointer to this structure in the user_namespace structure,
> in init_user_ns structure this pointer points to an init_binfmt_ns
> structure. And all new user namespaces point to this init structure.
> A new binfmt namespace structure is allocated if the binfmt_misc
> filesystem is mounted in a user namespace that is not the initial
> one but its binfmt namespace pointer points to the initial one.
> add override_creds()/revert_creds() around open_exec() in
> bm_register_write()
>
> v2: no new namespace, binfmt_misc data are now part of
> the mount namespace
> I put this in mount namespace instead of user namespace
> because the mount namespace is already needed and
> I don't want to force to have the user namespace for that.
> As this is a filesystem, it seems logic to have it here.
>
> This allows to define a new interpreter for each new container.
>
> But the main goal is to be able to chroot to a directory
> using a binfmt_misc interpreter without being root.
>
> I have a modified version of unshare at:
>
> git@github.com:vivier/util-linux.git branch unshare-chroot
>
> with some new options to unshare binfmt_misc namespace and to chroot
> to a directory.
>
> If you have a directory /chroot/powerpc/jessie containing debian for powerpc
> binaries and a qemu-ppc interpreter, you can do for instance:
>
> $ uname -a
> Linux fedora28-wor-2 4.19.0-rc5+ #18 SMP Mon Oct 1 00:32:34 CEST 2018 x86_64 x86_64 x86_64 GNU/Linux
> $ ./unshare --map-root-user --fork --pid \
> --load-interp ":qemu-ppc:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x14:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/qemu-ppc:OC" \
> --root=/chroot/powerpc/jessie /bin/bash -l
> # uname -a
> Linux fedora28-wor-2 4.19.0-rc5+ #18 SMP Mon Oct 1 00:32:34 CEST 2018 ppc GNU/Linux
> # id
> uid=0(root) gid=0(root) groups=0(root),65534(nogroup)
> # ls -l
> total 5940
> drwxr-xr-x. 2 nobody nogroup 4096 Aug 12 00:58 bin
> drwxr-xr-x. 2 nobody nogroup 4096 Jun 17 20:26 boot
> drwxr-xr-x. 4 nobody nogroup 4096 Aug 12 00:08 dev
> drwxr-xr-x. 42 nobody nogroup 4096 Sep 28 07:25 etc
> drwxr-xr-x. 3 nobody nogroup 4096 Sep 28 07:25 home
> drwxr-xr-x. 9 nobody nogroup 4096 Aug 12 00:58 lib
> drwxr-xr-x. 2 nobody nogroup 4096 Aug 12 00:08 media
> drwxr-xr-x. 2 nobody nogroup 4096 Aug 12 00:08 mnt
> drwxr-xr-x. 3 nobody nogroup 4096 Aug 12 13:09 opt
> dr-xr-xr-x. 143 nobody nogroup 0 Sep 30 23:02 proc
> -rwxr-xr-x. 1 nobody nogroup 6009712 Sep 28 07:22 qemu-ppc
> drwx------. 3 nobody nogroup 4096 Aug 12 12:54 root
> drwxr-xr-x. 3 nobody nogroup 4096 Aug 12 00:08 run
> drwxr-xr-x. 2 nobody nogroup 4096 Aug 12 00:58 sbin
> drwxr-xr-x. 2 nobody nogroup 4096 Aug 12 00:08 srv
> drwxr-xr-x. 2 nobody nogroup 4096 Apr 6 2015 sys
> drwxrwxrwt. 2 nobody nogroup 4096 Sep 28 10:31 tmp
> drwxr-xr-x. 10 nobody nogroup 4096 Aug 12 00:08 usr
> drwxr-xr-x. 11 nobody nogroup 4096 Aug 12 00:08 var
>
> If you want to use the qemu binary provided by your distro, you can use
>
> --load-interp ":qemu-ppc:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x14:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/bin/qemu-ppc-static:OCF"
>
> With the 'F' flag, qemu-ppc-static will be then loaded from the main root
> filesystem before switching to the chroot.
>
> Laurent Vivier (1):
> ns: add binfmt_misc to the user namespace
>
> fs/binfmt_misc.c | 111 ++++++++++++++++++++++++---------
> include/linux/user_namespace.h | 15 +++++
> kernel/user.c | 14 +++++
> kernel/user_namespace.c | 3 +
> 4 files changed, 115 insertions(+), 28 deletions(-)
>

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