Re: [PATCH v4 18/21] fuse: Add support for pid namespaces

From	Miklos Szeredi <mszeredi@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 18/21] fuse: Add support for pid namespaces
Date	2016-07-21 09:30 +0200
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On Wed, Jul 20, 2016 at 2:52 PM, Seth Forshee
<seth.forshee@canonical.com> wrote:

> It sounds like we need to remove the restriction on accessing the
> filesystem from a different pid namespace. I don't think this poses a
> security problem. However there's no pid mapping that is usable by the
> userspace fuse process, so what do we put in the fuse request? Probably
> the only candidates are 0 and 0xffffffff.
>
> So a question for the fuse developers - is one value or the other
> preferrable for fuse_in_header.pid when the pid cannot be mapped, and is
> this going to cause problems for any fuse filesystems? I suspect that
> few filesystems actually look at the pid anyway, and already for a
> filesystem mounted in a pid namespace the values being given to
> userspace won't be correct for the namespace of the fuse process.

pid = 0 sounds good.

The pid from the request is used for example to get the auxiliary
group list by libfuse (fuse_req_getgroups()).   That's not used by all
filesystems and it will return an error in case it can't find the proc
entry (which it won't for pid == 0).

It would be nice if we could transfer the group list through the
userspace/kernel protocol, since then it wouldn't depend on proc and
on being in the same pid namespace.  But that's another story.

Thanks,
Miklos

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Re: [PATCH v4 18/21] fuse: Add support for pid namespaces Sheng Yang <sheng@yasker.org> - 2016-07-20 04:50 +0200
  Re: [PATCH v4 18/21] fuse: Add support for pid namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-07-20 15:00 +0200
    Re: [PATCH v4 18/21] fuse: Add support for pid namespaces Sheng Yang <sheng@yasker.org> - 2016-07-21 00:30 +0200
    Re: [PATCH v4 18/21] fuse: Add support for pid namespaces Miklos Szeredi <mszeredi@redhat.com> - 2016-07-21 09:30 +0200

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