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

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Fri, Sep 14, 2018 at 07:46:17AM -0700, Petar Penkov wrote:
> From: Petar Penkov <ppenkov@google.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?

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?