On 7/22/22 7:20 AM, Paul Moore wrote:

On July 22, 2022 2:12:03 AM Martin KaFai Lau [off-list ref] wrote:

quoted

On Thu, Jul 21, 2022 at 12:28:04PM -0500, Frederick Lawler wrote:

quoted

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.

This patchset is in my review queue and assuming everything checks out, I expect to merge it after the upcoming merge window closes.

I would also need an ACK from the BPF LSM folks, but they're CC'd on this patchset.

Based on last weeks comments, should I go ahead and put up v4 for 
5.20-rc1 when that drops, or do I need to wait for more feedback?

--
paul-moore.com