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    SubjectRe: [CRIU] Introspecting userns relationships to other namespaces?
    On July 9, 2016 4:26:28 PM GMT+09:00, Andrew Vagin <> wrote:
    >On Fri, Jul 08, 2016 at 10:05:18PM -0500, Eric W. Biederman wrote:
    >> James Bottomley <> writes:
    >> > On Fri, 2016-07-08 at 18:52 -0500, Eric W. Biederman wrote:
    >> >> James Bottomley <> writes:
    >> >>
    >> >> > On July 8, 2016 1:38:19 PM PDT, Andrew Vagin
    >> >> > wrote:
    >> >>
    >> >> > > What do you think about the idea to mount nsfs and be able to
    >> >> > > look up any alive namespace by inum:
    >> >> >
    >> >> > I think I like it. It will give us a way to enter any extant
    >> >> > namespace. It will work for Eric's fs namespaces as well.
    >> >> > a /process/ns/<inum> Directory?
    >> >
    >> > As you understood, I meant /proc/ns/<inum> (damn mobile phone
    >> > completions).
    >> >
    >> >> *Shivers*
    >> >>
    >> >> That makes it very easy to bypass any existing controls that exist
    >> >> for getting at namespaces. It is true that everything of that
    >> >> is directory based but still.
    >> >>
    >> >> Plus I think it would serve as information leak to information
    >> >> outside of the container.
    >> >>
    >> >> An operation to get a user namespace file descriptor from some
    >> >> object sounds reasonably sane.
    >> >>
    >> >> A great big list of things sounds about as scary as it can get.
    >> >> is not the time to be making it easier to escape from containers.
    >> >
    >> > To be honest, I think this argument is rubbish. If we're afraid of
    >> > giving out a list of all the namespaces, it means we're afraid
    >> > some security bug and we're trying to obscure it by making the list
    >> > hard to get. All we've done is allayed fears about the bug but the
    >> > hackers still know the portals to get through.
    >> >
    >> > If such a bug exists, it will be possible to exploit it by simply
    >> > reconstructing the information from the individual process
    >> > so obscurity doesn't protect us and all it does is give us a false
    >> > sense of security. If such a bug doesn't exist, then all the
    >> > mechanisms currently in place (like no re-entry to prior namespace)
    >> > should protect us and we can give out the list.
    >> >
    >> > Let's deal with the world as we'd like it to be (no obscure
    >> > bugs) and accept the consequences and the responsibility for fixing
    >> > them if we turn out to be slightly incorrect. We'll end up in a
    >> > better place than security by obscurity would land us.
    >> No. That is not the fear. The permission checks on
    >> are different than if the namespace is bind mounted somewhere.
    >> That was done deliberately and with a reasonable amount of
    >> You are asking to throw those permission checks out. The answer is
    >> Furthermore there is a much clearer reason not to go with a list of
    >> namespaces. A list of all namespaces breaks CRIU. As you have
    >> it the list will change depending upon which machine you restore a
    >> checkpoint on. I honestly don't know what kind of havoc that will
    >> but it is certainly something we won't be able to checkpoint no
    >> how hard we try.
    >It's right. I hadn't thought about this.

    Me neither. Sorry for the prior outburst.

    I think this means we're back to exposing owning userns in the /proc /<pid >/ns directory.

    >> A global list of namespaces especially of the kind that you can open
    >> and get a handle to the namespace is just not appropriate.
    >> I know inode numbers comes darn close to names but they aren't really
    >> names and if it comes to it we can figure out how to preserve an
    >> applications view of it all across a checkpoint/restart. So far it
    >> hasn't proven necessary to preserve any inode numbers across
    >> checkpoint/restart but again it is theoretically possible if it
    >> necessary.
    >> Throwing away checkpoint/restart support for the sake of
    >> checkpoint/restart is a no-go.
    >> Containers fundamentally imply you don't have global visibility,
    >> and that is a good thing.
    >All these thoughts about security make me thinking that kcmp is what we
    >should use here. It's maybe something like this:
    >kcmp(pid1, pid2, KCMP_NS_USERNS, fd1, fd2)
    >- to check if userns of the fd1 namepsace is equal to the fd2 userns
    >kcmp(pid1, pid2, KCMP_NS_PARENT, fd1, fd2)
    >- to check if a parent namespace of the fd1 pidns is equal to fd pidns.
    >fd1 and fd2 is file descriptors to namespace files.
    >So if we want to build a hierarchy, we need to collect all namespaces
    >and then enumerate them to check dependencies with help of kcmp.

    Sure, but we need a method for opening the filehandles first .. .


    >> Eric

    Sent from my Android device with K-9 Mail. Please excuse my brevity.

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