> On 6/30/20 2:49 PM, Lorenzo Bianconi wrote:
> [...]
[...]
> > old_rcpu = xchg(&cmap->cpu_map[key_cpu], rcpu);
> > if (old_rcpu) {
> > + if (old_rcpu->prog)
> > + bpf_prog_put(old_rcpu->prog);
> > call_rcu(&old_rcpu->rcu, __cpu_map_entry_free);
> > INIT_WORK(&old_rcpu->kthread_stop_wq, cpu_map_kthread_stop);
> > schedule_work(&old_rcpu->kthread_stop_wq);
>
> Hm, not quite sure I follow the logic here. Why is the bpf_prog_put() not placed inside
> __cpu_map_entry_free(), for example? Wouldn't this at least leave a potential small race
> window of UAF given the rest is still live? If we already piggy-back from RCU side on
> rcpu entry, why not having it in __cpu_map_entry_free()?
ack right, thanks for spotting this issue. I guess we can even move
"bpf_prog_put(rcpu->prog)" in put_cpu_map_entry() so the last consumer
of bpf_cpu_map_entry will free the attached program. Agree?
Regards,
Lorenzo
>
> Thanks,
> Daniel
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