Re: [PATCH RFC v4 net-next 17/26] tracing: allow eBPF programs to be attached to events

[Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>]

On Fri, Aug 15, 2014 at 12:29 PM, Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org> wrote:
> On Fri, Aug 15, 2014 at 12:20 PM, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org> wrote:
>>>>
>>>> I don't think that fixing this should be a prerequisite for merging,
>>>> since the risk is so small.  Nonetheless, it would be nice.  (This
>>>> family of attacks has lead to several root vulnerabilities in the
>>>> past.)
>>>
>>> Ok. I think keeping a track of pid between open and write is kinda
>>> ugly.
>>
>> Agreed.
>>
>> TBH, I would just add a comment to the open implementation saying
>> that, if unprivileged or less privileged open is allowed, then this
>> needs to be fixed.
>
> ok. will do.
>
>>> Should we add some new CAP flag and check it for all file
>>> ops? Another option is to conditionally make open() of tracing
>>> files as cloexec...
>>
>> That won't help.  The same attack can be done with SCM_RIGHTS, and
>> cloexec can be cleared.
>
> ouch, can we then make ebpf FDs and may be debugfs FDs
> not passable at all? Otherwise it feels that generality and
> flexibility of FDs is becoming a burden.

I'm not sure there's much of a general problem.  The issue is when
there's an fd for which write(2) (or other
assumed-to-not-check-permissions calls like read, pread, pwrite, etc)
depend on context.  This is historically an issue for netlink and
various /proc files.

--Andy