Re: [PATCH v3 0/4] Introduce security_create_user_ns()

[Martin KaFai Lau]

On Thu, Jul 21, 2022 at 12:28:04PM -0500, Frederick Lawler wrote:
> While creating a LSM BPF MAC policy to block user namespace creation, we
> used the LSM cred_prepare hook because that is the closest hook to prevent
> a call to create_user_ns().
> 
> The calls look something like this:
> 
>     cred = prepare_creds()
>         security_prepare_creds()
>             call_int_hook(cred_prepare, ...
>     if (cred)
>         create_user_ns(cred)
> 
> We noticed that error codes were not propagated from this hook and
> introduced a patch [1] to propagate those errors.
> 
> The discussion notes that security_prepare_creds()
> is not appropriate for MAC policies, and instead the hook is
> meant for LSM authors to prepare credentials for mutation. [2]
> 
> Ultimately, we concluded that a better course of action is to introduce
> a new security hook for LSM authors. [3]
> 
> This patch set first introduces a new security_create_user_ns() function
> and userns_create LSM hook, then marks the hook as sleepable in BPF.
Patch 1 and 4 still need review from the lsm/security side.