[RFC] Add BPF_PROG_TYPE_CGROUP_IOCTL

[Kenny Ho]

Thanks for the reply.  Cgroup awareness is desired because the intent
is to use this for resource management as well (potentially along with
other cgroup controlled resources.)  I will dig into bpf_lsm and learn
more about it.

Regards,
Kenny


On Tue, Nov 3, 2020 at 12:32 AM Alexei Starovoitov
<alexei.starovoitov at gmail.com> wrote:
>
> On Mon, Nov 02, 2020 at 02:23:02PM -0500, Kenny Ho wrote:
> > Adding a few more emails from get_maintainer.pl and bumping this
> > thread since there hasn't been any comments so far.  Is this too
> > crazy?  Am I missing something fundamental?
>
> sorry for delay. Missed it earlier. Feel free to ping the mailing list
> sooner next time.
>
> > On Wed, Oct 7, 2020 at 11:24 AM Kenny Ho <Kenny.Ho at amd.com> wrote:
> > >
> > > This is a skeleton implementation to invite comments and generate
> > > discussion around the idea of introducing a bpf-cgroup program type to
> > > control ioctl access.  This is modelled after
> > > BPF_PROG_TYPE_CGROUP_DEVICE.  The premise is to allow system admins to
> > > write bpf programs to block some ioctl access, potentially in conjunction
> > > with data collected by other bpf programs stored in some bpf maps and
> > > with bpf_spin_lock.
> > >
> > > For example, a bpf program has been accumulating resource usaging
> > > statistic and a second bpf program of BPF_PROG_TYPE_CGROUP_IOCTL would
> > > block access to previously mentioned resource via ioctl when the stats
> > > stored in a bpf map reaches certain threshold.
> > >
> > > Like BPF_PROG_TYPE_CGROUP_DEVICE, the default is permissive (i.e.,
> > > ioctls are not blocked if no bpf program is present for the cgroup.) to
> > > maintain current interface behaviour when this functionality is unused.
> > >
> > > Performance impact to ioctl calls is minimal as bpf's in-kernel verifier
> > > ensure attached bpf programs cannot crash and always terminate quickly.
> > >
> > > TODOs:
> > > - correct usage of the verifier
> > > - toolings
> > > - samples
> > > - device driver may provide helper functions that take
> > > bpf_cgroup_ioctl_ctx and return something more useful for specific
> > > device
> > >
> > > Signed-off-by: Kenny Ho <Kenny.Ho at amd.com>
> ...
> > > @@ -45,6 +46,10 @@ long vfs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> > >         if (!filp->f_op->unlocked_ioctl)
> > >                 goto out;
> > >
> > > +       error = BPF_CGROUP_RUN_PROG_IOCTL(filp, cmd, arg);
> > > +       if (error)
> > > +               goto out;
> > > +
>
> That's a bit problematic, since we have bpf_lsm now.
> Could you use security_file_ioctl hook and do the same filtering there?
> It's not cgroup based though. Is it a concern?
> If cgroup scoping is really necessary then it's probably better
> to add it to bpf_lsm. Then all hooks will become cgroup aware.