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From: Lorenzo Bianconi <lorenzo@kernel.org>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, davem@davemloft.net,
	ast@kernel.org, brouer@redhat.com, toke@redhat.com,
	lorenzo.bianconi@redhat.com, dsahern@kernel.org,
	andrii.nakryiko@gmail.com
Subject: Re: [PATCH v5 bpf-next 5/9] bpf: cpumap: add the possibility to attach an eBPF program to cpumap
Date: Fri, 3 Jul 2020 22:48:10 +0200
Message-ID: <20200703204810.GB1321275@localhost.localdomain> (raw)
In-Reply-To: <1f4af1f3-10cf-57ca-4171-11d3bff51c99@iogearbox.net>


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> 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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  reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-30 12:49 [PATCH v5 bpf-next 0/9] introduce support for XDP programs in CPUMAP Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 1/9] cpumap: use non-locked version __ptr_ring_consume_batched Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 2/9] net: refactor xdp_convert_buff_to_frame Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 3/9] samples/bpf: xdp_redirect_cpu_user: do not update bpf maps in option loop Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 4/9] cpumap: formalize map value as a named struct Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 5/9] bpf: cpumap: add the possibility to attach an eBPF program to cpumap Lorenzo Bianconi
2020-07-01 23:02   ` Daniel Borkmann
2020-07-03 15:46     ` Lorenzo Bianconi
2020-07-01 23:39   ` Daniel Borkmann
2020-07-03 20:48     ` Lorenzo Bianconi [this message]
2020-07-03 22:24       ` Daniel Borkmann
2020-06-30 12:49 ` [PATCH v5 bpf-next 6/9] bpf: cpumap: implement XDP_REDIRECT for eBPF programs attached to map entries Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 7/9] libbpf: add SEC name for xdp programs attached to CPUMAP Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 8/9] samples/bpf: xdp_redirect_cpu: load a eBPF program on cpumap Lorenzo Bianconi
2020-06-30 12:49 ` [PATCH v5 bpf-next 9/9] selftest: add tests for XDP programs in CPUMAP entries Lorenzo Bianconi

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