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SubjectRe: [RFC] Allow user namespace inside chroot
Jann Horn <jannh@google.com> writes:

> On Mon, Oct 15, 2018 at 7:10 PM <nagarathnam.muthusamy@oracle.com> wrote:
>> @@ -1281,7 +1285,7 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
>> return -ENOMEM;
>>
>> put_user_ns(cred->user_ns);
>> - set_cred_user_ns(cred, get_user_ns(user_ns));
>> + set_cred_user_ns(cred, get_user_ns(user_ns), 0);
>
> This looks bogus. With this, I think your restriction can be bypassed
> if process A forks a child B, B creates a new user namespace, then A
> enters the user namespace with setns() and has full capabilities. Am I
> missing something?

Nope. I feel silly for missing that angle.

Even without the full capabilities the userns_install angle will place
you at the root of the mount namespace outside of the chroot.

At which point I have visions of the special cases multiplying like
bunnies make this work. Without a very strong case I don't like this at all.

Eric



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