From: Jakub Sitnicki <jakub@cloudflare.com>
To: Lorenz Bauer <lmb@cloudflare.com>
Cc: bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
kernel-team <kernel-team@cloudflare.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Marek Majkowski <marek@cloudflare.com>
Subject: Re: [PATCH bpf-next v3 04/16] inet: Run SK_LOOKUP BPF program on socket lookup
Date: Mon, 06 Jul 2020 13:24:59 +0200 [thread overview]
Message-ID: <87k0zgj378.fsf@cloudflare.com> (raw)
In-Reply-To: <CACAyw98MsdcVkFPpXatr3F6j6F79KuTqcpwpB6TNpLBVuGKJTQ@mail.gmail.com>
On Thu, Jul 02, 2020 at 03:19 PM CEST, Lorenz Bauer wrote:
> On Thu, 2 Jul 2020 at 13:46, Jakub Sitnicki <jakub@cloudflare.com> wrote:
>>
>> On Thu, Jul 02, 2020 at 12:27 PM CEST, Lorenz Bauer wrote:
>> > On Thu, 2 Jul 2020 at 10:24, Jakub Sitnicki <jakub@cloudflare.com> wrote:
>> >>
>> >> Run a BPF program before looking up a listening socket on the receive path.
>> >> Program selects a listening socket to yield as result of socket lookup by
>> >> calling bpf_sk_assign() helper and returning BPF_REDIRECT (7) code.
>> >>
>> >> Alternatively, program can also fail the lookup by returning with
>> >> BPF_DROP (1), or let the lookup continue as usual with BPF_OK (0) on
>> >> return. Other return values are treated the same as BPF_OK.
>> >
>> > I'd prefer if other values were treated as BPF_DROP, with other semantics
>> > unchanged. Otherwise we won't be able to introduce new semantics
>> > without potentially breaking user code.
>>
>> That might be surprising or even risky. If you attach a badly written
>> program that say returns a negative value, it will drop all TCP SYNs and
>> UDP traffic.
>
> I think if you do that all bets are off anyways. No use in trying to stagger on.
> Being stricter here will actually make it easier to for a developer to ensure
> that their program is doing the right thing.
>
> My point about future extensions also still stands.
We've chatted with Lorenz off-list about pros & cons of defaulting to
drop on illegal return code from a BPF program.
On the upside, it is consistent with XDP, SK_REUSEPORT, and SK_SKB
(sockmap) program types.
TC BPF ignores illegal return values, unspecified action means no
action, so no drop. While CGROUP_INET_INGRESS and SOCKET_FILTER look
only at the lowest bit ("ret & 1"), so it is a roulette.
Then there is also the extensibility argument. If we allow traffic to
pass to regular socket lookup on illegal return code from BPF, and users
start to rely on that, then it will be hard or impossible to repurpose
an illegal return value for something else.
Downside of defaulting to drop is that you can accidentally lock
yourself out, e.g. lose SSH access, by attaching a buggy program.
Being consistent with other existing program types is what convinces me
most to set default to drop, so I'll make the change in v4 unless there
are objections.
[...]
next prev parent reply other threads:[~2020-07-06 11:25 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-02 9:24 [PATCH bpf-next v3 00/16] Run a BPF program on socket lookup Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 01/16] bpf, netns: Handle multiple link attachments Jakub Sitnicki
2020-07-09 3:44 ` Andrii Nakryiko
2020-07-09 12:49 ` Jakub Sitnicki
2020-07-09 22:02 ` Andrii Nakryiko
2020-07-10 19:23 ` Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 02/16] bpf: Introduce SK_LOOKUP program type with a dedicated attach point Jakub Sitnicki
2020-07-04 18:42 ` Yonghong Song
2020-07-06 11:44 ` Jakub Sitnicki
2020-07-05 9:20 ` kernel test robot
2020-07-05 9:20 ` kernel test robot
2020-07-05 9:20 ` [RFC PATCH] bpf: sk_lookup_prog_ops can be static kernel test robot
2020-07-05 9:20 ` kernel test robot
2020-07-07 9:21 ` [PATCH bpf-next v3 02/16] bpf: Introduce SK_LOOKUP program type with a dedicated attach point Jakub Sitnicki
2020-07-09 4:08 ` Andrii Nakryiko
2020-07-09 13:25 ` Jakub Sitnicki
2020-07-09 23:09 ` Andrii Nakryiko
2020-07-10 8:55 ` Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 03/16] inet: Extract helper for selecting socket from reuseport group Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 04/16] inet: Run SK_LOOKUP BPF program on socket lookup Jakub Sitnicki
2020-07-02 10:27 ` Lorenz Bauer
2020-07-02 12:46 ` Jakub Sitnicki
2020-07-02 13:19 ` Lorenz Bauer
2020-07-06 11:24 ` Jakub Sitnicki [this message]
2020-07-06 12:06 ` Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 05/16] inet6: Extract helper for selecting socket from reuseport group Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 06/16] inet6: Run SK_LOOKUP BPF program on socket lookup Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 07/16] udp: Extract helper for selecting socket from reuseport group Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 08/16] udp: Run SK_LOOKUP BPF program on socket lookup Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 09/16] udp6: Extract helper for selecting socket from reuseport group Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 10/16] udp6: Run SK_LOOKUP BPF program on socket lookup Jakub Sitnicki
2020-07-02 14:51 ` kernel test robot
2020-07-02 14:51 ` kernel test robot
2020-07-03 13:04 ` Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 11/16] bpf: Sync linux/bpf.h to tools/ Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 12/16] libbpf: Add support for SK_LOOKUP program type Jakub Sitnicki
2020-07-09 4:23 ` Andrii Nakryiko
2020-07-09 15:51 ` Jakub Sitnicki
2020-07-09 23:13 ` Andrii Nakryiko
2020-07-10 8:37 ` Jakub Sitnicki
2020-07-10 18:55 ` Andrii Nakryiko
2020-07-10 19:24 ` Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 13/16] tools/bpftool: Add name mappings for SK_LOOKUP prog and attach type Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 14/16] selftests/bpf: Add verifier tests for bpf_sk_lookup context access Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 15/16] selftests/bpf: Rename test_sk_lookup_kern.c to test_ref_track_kern.c Jakub Sitnicki
2020-07-02 9:24 ` [PATCH bpf-next v3 16/16] selftests/bpf: Tests for BPF_SK_LOOKUP attach point Jakub Sitnicki
2020-07-02 11:01 ` Lorenz Bauer
2020-07-02 12:59 ` Jakub Sitnicki
2020-07-09 4:28 ` Andrii Nakryiko
2020-07-09 15:54 ` Jakub Sitnicki
2020-07-02 11:05 ` [PATCH bpf-next v3 00/16] Run a BPF program on socket lookup Lorenz Bauer
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