netdev - Re: [bpf-next, v4 0/5] Introduce eBPF flow dissector

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Message-ID: <CAG4SDVVib24cyjvzzKBYbvhY8fgMZwcfq5jwCNuX3iipO_+P0w@mail.gmail.com>
Date:   Fri, 14 Sep 2018 14:49:53 -0700
From:   Petar Penkov <ppenkov@...gle.com>
To:     Y Song <ys114321@...il.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Petar Penkov <peterpenkov96@...il.com>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        simon.horman@...ronome.com, Edward Cree <ecree@...arflare.com>,
        songliubraving@...com, Tom Herbert <tom@...bertland.com>
Subject: Re: [bpf-next, v4 0/5] Introduce eBPF flow dissector

On Fri, Sep 14, 2018 at 2:47 PM, Y Song <ys114321@...il.com> wrote:
> On Fri, Sep 14, 2018 at 12:24 PM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
>>
>> On Fri, Sep 14, 2018 at 07:46:17AM -0700, Petar Penkov wrote:
>> > From: Petar Penkov <ppenkov@...gle.com>
>> >
>> > This patch series hardens the RX stack by allowing flow dissection in BPF,
>> > as previously discussed [1]. Because of the rigorous checks of the BPF
>> > verifier, this provides significant security guarantees. In particular, the
>> > BPF flow dissector cannot get inside of an infinite loop, as with
>> > CVE-2013-4348, because BPF programs are guaranteed to terminate. It cannot
>> > read outside of packet bounds, because all memory accesses are checked.
>> > Also, with BPF the administrator can decide which protocols to support,
>> > reducing potential attack surface. Rarely encountered protocols can be
>> > excluded from dissection and the program can be updated without kernel
>> > recompile or reboot if a bug is discovered.
>> >
>> > Patch 1 adds infrastructure to execute a BPF program in __skb_flow_dissect.
>> > This includes a new BPF program and attach type.
>> >
>> > Patch 2 adds the new BPF flow dissector definitions to tools/uapi.
>> >
>> > Patch 3 adds support for the new BPF program type to libbpf and bpftool.
>> >
>> > Patch 4 adds a flow dissector program in BPF. This parses most protocols in
>> > __skb_flow_dissect in BPF for a subset of flow keys (basic, control, ports,
>> > and address types).
>> >
>> > Patch 5 adds a selftest that attaches the BPF program to the flow dissector
>> > and sends traffic with different levels of encapsulation.
>> >
>> > Performance Evaluation:
>> > The in-kernel implementation was compared against the demo program from
>> > patch 4 using the test in patch 5 with IPv4/UDP traffic over 10 seconds.
>> >       $perf record -a -C 4 taskset -c 4 ./test_flow_dissector -i 4 -f 8 \
>> >               -t 10
>>
>> Looks great. Applied to bpf-next with one extra patch:
>>  SEC("dissect")
>> -int dissect(struct __sk_buff *skb)
>> +int _dissect(struct __sk_buff *skb)
>>
>> otherwise the test doesn't build.
>> I'm not sure how it builds for you. Which llvm did you use?
>
> This is a known issue. IIRC, llvm <= 4 should be okay and llvm >= 5 would fail.
>
I was running a much older version of llvm so I imagine this was the
issue. Thanks for the fix!
>>
>> Also above command works and ipv4 test in ./test_flow_dissector.sh
>> is passing as well, but it still fails at the end for me:
>> ./test_flow_dissector.sh
>> bpffs not mounted. Mounting...
>> 0: IP
>> 1: IPV6
>> 2: IPV6OP
>> 3: IPV6FR
>> 4: MPLS
>> 5: VLAN
>> Testing IPv4...
>> inner.dest4: 127.0.0.1
>> inner.source4: 127.0.0.3
>> pkts: tx=10 rx=10
>> inner.dest4: 127.0.0.1
>> inner.source4: 127.0.0.3
>> pkts: tx=10 rx=0
>> inner.dest4: 127.0.0.1
>> inner.source4: 127.0.0.3
>> pkts: tx=10 rx=10
>> Testing IPIP...
>> tunnels before test:
>> tunl0: any/ip remote any local any ttl inherit nopmtudisc
>> sit_test_LV5N: any/ip remote 127.0.0.2 local 127.0.0.1 dev lo ttl inherit
>> ipip_test_LV5N: any/ip remote 127.0.0.2 local 127.0.0.1 dev lo ttl inherit
>> sit0: ipv6/ip remote any local any ttl 64 nopmtudisc
>> gre_test_LV5N: gre/ip remote 127.0.0.2 local 127.0.0.1 dev lo ttl inherit
>> gre0: gre/ip remote any local any ttl inherit nopmtudisc
>> inner.dest4: 192.168.0.1
>> inner.source4: 1.1.1.1
>> encap proto:   4
>> outer.dest4: 127.0.0.1
>> outer.source4: 127.0.0.2
>> pkts: tx=10 rx=0
>> tunnels after test:
>> tunl0: any/ip remote any local any ttl inherit nopmtudisc
>> sit0: ipv6/ip remote any local any ttl 64 nopmtudisc
>> gre0: gre/ip remote any local any ttl inherit nopmtudisc
>> selftests: test_flow_dissector [FAILED]
>>
>> is it something in my setup or test is broken?
>>
I just reran the test and it is passing. We will investigate what
could be causing the issue.