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.
