From: Martin KaFai Lau <martin.lau@linux•dev>
To: Mahe Tardy <mahe.tardy@gmail•com>
Cc: alexei.starovoitov@gmail•com, andrii@kernel•org, ast@kernel•org,
bpf@vger•kernel.org, coreteam@netfilter•org,
daniel@iogearbox•net, fw@strlen•de, john.fastabend@gmail•com,
netdev@vger•kernel.org, netfilter-devel@vger•kernel.org,
oe-kbuild-all@lists•linux.dev, pablo@netfilter•org,
lkp@intel•com
Subject: Re: [PATCH bpf-next v3 4/4] selftests/bpf: add icmp_send_unreach kfunc tests
Date: Tue, 29 Jul 2025 17:01:24 -0700 [thread overview]
Message-ID: <cdd57fe6-ed8c-4cc9-a1dc-8563160a71e4@linux.dev> (raw)
In-Reply-To: <996bb1dd-e72e-4515-a60f-c5f31b840459@linux.dev>
On 7/29/25 4:27 PM, Martin KaFai Lau wrote:
> On 7/29/25 2:09 AM, Mahe Tardy wrote:
>> On Mon, Jul 28, 2025 at 06:18:11PM -0700, Martin KaFai Lau wrote:
>>> On 7/28/25 2:43 AM, Mahe Tardy wrote:
>>>> +SEC("cgroup_skb/egress")
>>>> +int egress(struct __sk_buff *skb)
>>>> +{
>>>> + void *data = (void *)(long)skb->data;
>>>> + void *data_end = (void *)(long)skb->data_end;
>>>> + struct iphdr *iph;
>>>> + struct tcphdr *tcph;
>>>> +
>>>> + iph = data;
>>>> + if ((void *)(iph + 1) > data_end || iph->version != 4 ||
>>>> + iph->protocol != IPPROTO_TCP || iph->daddr != bpf_htonl(SERVER_IP))
>>>> + return SK_PASS;
>>>> +
>>>> + tcph = (void *)iph + iph->ihl * 4;
>>>> + if ((void *)(tcph + 1) > data_end ||
>>>> + tcph->dest != bpf_htons(SERVER_PORT))
>>>> + return SK_PASS;
>>>> +
>>>> + kfunc_ret = bpf_icmp_send_unreach(skb, unreach_code);
>>>> +
>>>> + /* returns SK_PASS to execute the test case quicker */
>>>
>>> Do you know why the user space is slower if 0 (SK_DROP) is used?
>>
>> I tried to write my understanding of this in the commit description:
>>
>> "Note that the BPF program returns SK_PASS to let the connection being
>> established to finish the test cases quicker. Otherwise, you have to
>> wait for the TCP three-way handshake to timeout in the kernel and
>> retrieve the errno translated from the unreach code set by the ICMP
>> control message."
>
> This feels like a bit hacky to let the 3WHS finished while the objective of the
> patch set is to drop it. It is not unusual for people to directly borrow this
> code. Does non blocking connect() help?
>
After reading more on how sk_err_soft is used, non blocking won't help. I think
I see why tcp rst is better.
next prev parent reply other threads:[~2025-07-30 0:01 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAADnVQKq_-=N7eJoup6AqFngoocT+D02NF0md_3mi2Vcrw09nQ@mail.gmail.com>
2025-07-25 18:53 ` [PATCH bpf-next v1 0/4] bpf: add icmp_send_unreach kfunc Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 1/4] net: move netfilter nf_reject_fill_skb_dst to core ipv4 Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 2/4] net: move netfilter nf_reject6_fill_skb_dst to core ipv6 Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 3/4] bpf: add bpf_icmp_send_unreach cgroup_skb kfunc Mahe Tardy
2025-07-27 1:49 ` kernel test robot
2025-07-28 9:43 ` [PATCH bpf-next v3 0/4] bpf: add icmp_send_unreach kfunc Mahe Tardy
2025-07-28 9:43 ` [PATCH bpf-next v3 1/4] net: move netfilter nf_reject_fill_skb_dst to core ipv4 Mahe Tardy
2025-07-28 9:43 ` [PATCH bpf-next v3 2/4] net: move netfilter nf_reject6_fill_skb_dst to core ipv6 Mahe Tardy
2025-07-28 9:43 ` [PATCH bpf-next v3 3/4] bpf: add bpf_icmp_send_unreach cgroup_skb kfunc Mahe Tardy
2025-07-28 20:10 ` kernel test robot
2025-07-29 1:05 ` Martin KaFai Lau
2025-07-29 10:06 ` Mahe Tardy
2025-07-29 23:13 ` Martin KaFai Lau
2025-07-28 9:43 ` [PATCH bpf-next v3 4/4] selftests/bpf: add icmp_send_unreach kfunc tests Mahe Tardy
2025-07-28 15:40 ` Yonghong Song
2025-07-28 15:59 ` Mahe Tardy
2025-07-29 1:18 ` Martin KaFai Lau
2025-07-29 9:09 ` Mahe Tardy
2025-07-29 23:27 ` Martin KaFai Lau
2025-07-30 0:01 ` Martin KaFai Lau [this message]
2025-07-30 0:32 ` Martin KaFai Lau
2025-08-05 23:26 ` Jordan Rife
2025-07-29 1:21 ` [PATCH bpf-next v3 0/4] bpf: add icmp_send_unreach kfunc Martin KaFai Lau
2025-07-29 9:53 ` Mahe Tardy
2025-07-30 1:54 ` Martin KaFai Lau
2025-08-01 18:50 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 0/6] " Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 1/6] net: move netfilter nf_reject_fill_skb_dst to core ipv4 Mahe Tardy
2026-04-20 11:36 ` bot+bpf-ci
2026-04-20 13:04 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 2/6] net: move netfilter nf_reject6_fill_skb_dst to core ipv6 Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 3/6] bpf: add bpf_icmp_send_unreach kfunc Mahe Tardy
2026-04-20 11:36 ` bot+bpf-ci
2026-04-20 13:07 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 4/6] selftests/bpf: add icmp_send_unreach kfunc tests Mahe Tardy
2026-04-20 11:36 ` bot+bpf-ci
2026-04-20 13:08 ` Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 5/6] selftests/bpf: add icmp_send_unreach kfunc IPv6 tests Mahe Tardy
2026-04-20 10:58 ` [PATCH bpf-next v4 6/6] selftests/bpf: add icmp_send_unreach_recursion test Mahe Tardy
2025-07-25 18:53 ` [PATCH bpf-next v2 4/4] selftests/bpf: add icmp_send_unreach kfunc tests Mahe Tardy
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