Re: [PATCH] [RFC] bpf: tracing: new helper bpf_get_current_cgroup_ino

[Daniel Borkmann]

On 05/23/2018 06:31 AM, Y Song wrote:
> On Tue, May 22, 2018 at 8:35 PM, Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
>> On Tue, May 22, 2018 at 08:33:24PM -0700, Y Song wrote:
>>> +       struct cgroup *cgrp = task_dfl_cgroup(current);
>>> +       if (!cgrp)
>>> +               return -EINVAL;
>>
>> why this check is needed?
> 
> No reason :-) Originally I am concerned whether it is possible cgrp
> could be NULL.
> By looking at the code, it SEEMS to me that it could not be NULL, but I am not
> 100% sure (as I am not a cgroup expert). Since you are asking,
> probably means it cannot be NULL, so will remove it in formal upstream patch.

Aside from this the cgrp->kn->id.id is also u64, so overlapping this with
error codes we'll get into a similar issue as with bpf_perf_event_read().