netdev - Re: [PATCH bpf-next v8 11/11] selftests/bpf: verify lsm

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Date:   Thu, 2 Jun 2022 22:38:48 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Subject: Re: [PATCH bpf-next v8 11/11] selftests/bpf: verify lsm_cgroup
 struct sock access

On Thu, Jun 02, 2022 at 06:59:47PM -0700, Stanislav Fomichev wrote:
> On Thu, Jun 2, 2022 at 6:52 PM Martin KaFai Lau <kafai@...com> wrote:
> >
> > On Wed, Jun 01, 2022 at 12:02:18PM -0700, Stanislav Fomichev wrote:
> > > sk_priority & sk_mark are writable, the rest is readonly.
> > >
> > > One interesting thing here is that the verifier doesn't
> > > really force me to add NULL checks anywhere :-/
> > Are you aware if it is possible to get a NULL sk from some of the
> > bpf_lsm hooks ?
> 
> No, I don't think it's relevant for lsm hooks. I'm more concerned
> about fentry/fexit which supposedly should go through the same
> verifier path and can be attached everywhere?
fentry/fexit is BPF_READ.  It will be marked with BPF_PROBE_MEM
and the fault will be handled by the bpf extable handler.

If the lsm hooks cannot get a NULL sk, BPF_WRITE on the sk_prioirity and
sk_mark is fine.

Took a first pass on the set and will take a closer look.