netdev - Re: [PATCH bpf-next v8 03/11] bpf: per-cgroup lsm flavor

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Date:   Sat, 4 Jun 2022 01:27:06 -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 03/11] bpf: per-cgroup lsm flavor

On Fri, Jun 03, 2022 at 11:11:58PM -0700, Martin KaFai Lau wrote:
> > @@ -549,9 +655,15 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
> >  	bpf_cgroup_storages_assign(pl->storage, storage);
> >  	cgrp->bpf.flags[atype] = saved_flags;
> >  
> > +	if (type == BPF_LSM_CGROUP && !old_prog) {
> hmm... I think this "!old_prog" test should not be here.
> 
> In allow_multi, old_prog can be NULL but it still needs
> to bump the shim_link's refcnt by calling
> bpf_trampoline_link_cgroup_shim().
> 
> This is a bit tricky.  Does it make sense ?
I think I read the "!"old_prog upside-down.  I think I got the
intention here now after reading some latter patches.
It is to save a bpf_trampoline_link_cgroup_shim() and unlink
for the replace case ?  I would prefer not to do this.
It is quite confusing to read and does not save much.

> 
> > +		err = bpf_trampoline_link_cgroup_shim(new_prog, &tgt_info, atype);
> > +		if (err)
> > +			goto cleanup;
> > +	}
> > +
> >  	err = update_effective_progs(cgrp, atype);
> >  	if (err)
> > -		goto cleanup;
> > +		goto cleanup_trampoline;
> >  
> >  	if (old_prog)
> Then it needs a bpf_trampoline_unlink_cgroup_shim(old_prog) here.
> 
> >  		bpf_prog_put(old_prog);
> > @@ -560,6 +672,10 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
> >  	bpf_cgroup_storages_link(new_storage, cgrp, type);
> >  	return 0;
> >  
> > +cleanup_trampoline:
> > +	if (type == BPF_LSM_CGROUP && !old_prog)
> The "!old_prog" test should also be removed.
> 
> > +		bpf_trampoline_unlink_cgroup_shim(new_prog);
> > +
> >  cleanup:
> >  	if (old_prog) {
> >  		pl->prog = old_prog;