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tailhook / unshare

The low-level linux containers creation library for rust
Apache License 2.0
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pivot_root fails with user namespace used #14

Open magicyuli opened 5 years ago

magicyuli commented 5 years ago

pivot_root succeeds if user namespace is not used, but fails with EINVAL (os error 22). Bind mounting the new_root to itself solves it. I think that's a hack used by go example as well. Maybe the CloneCb should include this logic?

Environment: Xenial 4.9.125-linuxkit #1 SMP Fri Sep 7 08:20:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

magicyuli commented 5 years ago

Or add an after_clone callback? There's currently a before_exec callback, which is called just right before execve.

tailhook commented 5 years ago

Hi!

I'm not sure it's because of user namespace. Isn't it because pivot_root requires both things to be mountpoints not mere directories?

I'm all for adding documentation describing the issue. But I don't think this should be done always. Adding a convenience method may be okay, though.

magicyuli commented 5 years ago

Thanks for the prompt response!

Yeah, I did make sure the new_root was a mount point, and put_old had nothing mounted to it, and was under new_root. Without using the user namespace it works without any problem, and that's why I think user namespace plays a part here.