Re: [RFC PATCH -mm 0/4] mm, security, bpf: Fine-grained control over memory policy adjustments with lsm bpf

[Casey Schaufler <casey@schaufler-ca.com>]

On 11/14/2023 3:59 AM, Yafang Shao wrote:
> On Tue, Nov 14, 2023 at 6:15 PM Michal Hocko <mhocko@suse.com> wrote:
>> On Mon 13-11-23 11:15:06, Yafang Shao wrote:
>>> On Mon, Nov 13, 2023 at 12:45 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>> On 11/11/2023 11:34 PM, Yafang Shao wrote:
>>>>> Background
>>>>> ==========
>>>>>
>>>>> In our containerized environment, we've identified unexpected OOM events
>>>>> where the OOM-killer terminates tasks despite having ample free memory.
>>>>> This anomaly is traced back to tasks within a container using mbind(2) to
>>>>> bind memory to a specific NUMA node. When the allocated memory on this node
>>>>> is exhausted, the OOM-killer, prioritizing tasks based on oom_score,
>>>>> indiscriminately kills tasks. This becomes more critical with guaranteed
>>>>> tasks (oom_score_adj: -998) aggravating the issue.
>>>> Is there some reason why you can't fix the callers of mbind(2)?
>>>> This looks like an user space configuration error rather than a
>>>> system security issue.
>>> It appears my initial description may have caused confusion. In this
>>> scenario, the caller is an unprivileged user lacking any capabilities.
>>> While a privileged user, such as root, experiencing this issue might
>>> indicate a user space configuration error, the concerning aspect is
>>> the potential for an unprivileged user to disrupt the system easily.
>>> If this is perceived as a misconfiguration, the question arises: What
>>> is the correct configuration to prevent an unprivileged user from
>>> utilizing mbind(2)?"
>> How is this any different than a non NUMA (mbind) situation?
> In a UMA system, each gigabyte of memory carries the same cost.
> Conversely, in a NUMA architecture, opting to confine processes within
> a specific NUMA node incurs additional costs. In the worst-case
> scenario, if all containers opt to bind their memory exclusively to
> specific nodes, it will result in significant memory wastage.

That still sounds like you've misconfigured your containers such
that they expect to get more memory than is available, and that
they have more control over it than they really do.


>> You can
>> still have an unprivileged user to allocate just until the OOM triggers
>> and disrupt other workload consuming more memory. Sure the mempolicy
>> based OOM is less precise and it might select a victim with only a small
>> consumption on a target NUMA node but fundamentally the situation is
>> very similar. I do not think disallowing mbind specifically is solving a
>> real problem.
> How would you recommend addressing this more effectively?
>