{"id":2225109,"url":"http://patchwork.ozlabs.org/api/1.1/covers/2225109/?format=json","web_url":"http://patchwork.ozlabs.org/project/netfilter-devel/cover/20260420105816.72168-1-mahe.tardy@gmail.com/","project":{"id":26,"url":"http://patchwork.ozlabs.org/api/1.1/projects/26/?format=json","name":"Netfilter Development","link_name":"netfilter-devel","list_id":"netfilter-devel.vger.kernel.org","list_email":"netfilter-devel@vger.kernel.org","web_url":null,"scm_url":null,"webscm_url":null},"msgid":"<20260420105816.72168-1-mahe.tardy@gmail.com>","date":"2026-04-20T10:58:10","name":"[bpf-next,v4,0/6] bpf: add icmp_send_unreach kfunc","submitter":{"id":91349,"url":"http://patchwork.ozlabs.org/api/1.1/people/91349/?format=json","name":"Mahe Tardy","email":"mahe.tardy@gmail.com"},"mbox":"http://patchwork.ozlabs.org/project/netfilter-devel/cover/20260420105816.72168-1-mahe.tardy@gmail.com/mbox/","series":[{"id":500597,"url":"http://patchwork.ozlabs.org/api/1.1/series/500597/?format=json","web_url":"http://patchwork.ozlabs.org/project/netfilter-devel/list/?series=500597","date":"2026-04-20T10:58:10","name":"bpf: add icmp_send_unreach kfunc","version":4,"mbox":"http://patchwork.ozlabs.org/series/500597/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/covers/2225109/comments/","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","netfilter-devel@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=TqqLys1i;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=2600:3c04:e001:36c::12fc:5321; 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The goal is to allow cgroup_skb programs to\nactively reject east-west traffic, similarly to what is possible to do\nwith netfilter reject target.\n\nThe first step to implement this is using ICMP control messages, with\nthe ICMP_DEST_UNREACH type with various code ICMP_NET_UNREACH,\nICMP_HOST_UNREACH, ICMP_PROT_UNREACH, etc. This is easier to implement\nthan a TCP RST reply and will already hint the client TCP stack to abort\nthe connection and not retry extensively.\n\nNote that this is different than the sock_destroy kfunc, that along\ncalls tcp_abort and thus sends a reset, destroying the underlying\nsocket.\n\nCaveats of this kfunc design are that a program can call this function N\ntimes, thus send N ICMP unreach control messages and that the program\ncan return from the BPF filter with pass leading to a potential\nconfusing situation where the TCP connection was established while the\nclient received ICMP_DEST_UNREACH messages.\n\nInitially, this kfunc was added only to cgroup_skb programs, Alexei\nsuggested not creating its own kfunc set and adding it to the more\nglobal bpf_kfunc_set_skb. Now that recursion is handled and I realized,\nthanks to Martin, that fetching the dst route might be only useful in\nsituation in which the packet was not yet routed, I decided to extend\nthe kfunc to more program types and route the packet only if needed.\n\nv2 updates:\n- fix a build error from a missing function call rename;\n- avoid changing return line in bpf_kfunc_init;\n- return SK_DROP from the kfunc (similarly to bpf_redirect);\n- check the return value in the selftest.\n\nv3 update:\n- fix an undefined reference build error.\n\nv4 updates:\n- prevent the kfunc to be called recursively and add a test (thanks to\n Martin).\n- do not fetch dst route when unnecessary (thanks to Martin).\n- extend the test for IPv6 (thanks to Martin).\n- use SK_DROP in examples and use non blocking sockets for testing\n (thanks to Martin).\n- test when the kfunc returns -EINVAL (thanks to Jordan).\n- add the kfunc to bpf_kfunc_set_skb as suggested by Alexei.\n- guard the IPv4 parts with IS_ENABLED(CONFIG_INET).\n- fix a wrong initial value for client_fd (thanks to Yonghong).\n- add documentation to the kfunc.\n- to Jordan: I couldn't include because of redefines from\n .\n\n[^1]: https://lwn.net/Articles/1022034/\n\nMahe Tardy (6):\n net: move netfilter nf_reject_fill_skb_dst to core ipv4\n net: move netfilter nf_reject6_fill_skb_dst to core ipv6\n bpf: add bpf_icmp_send_unreach kfunc\n selftests/bpf: add icmp_send_unreach kfunc tests\n selftests/bpf: add icmp_send_unreach kfunc IPv6 tests\n selftests/bpf: add icmp_send_unreach_recursion test\n\n include/net/ip6_route.h | 2 +\n include/net/route.h | 1 +\n net/core/filter.c | 85 ++++++++\n net/ipv4/netfilter/nf_reject_ipv4.c | 19 +-\n net/ipv4/route.c | 15 ++\n net/ipv6/netfilter/nf_reject_ipv6.c | 17 +-\n net/ipv6/route.c | 18 ++\n .../bpf/prog_tests/icmp_send_unreach_kfunc.c | 202 ++++++++++++++++++\n .../selftests/bpf/progs/icmp_send_unreach.c | 100 +++++++++\n 9 files changed, 426 insertions(+), 33 deletions(-)\n create mode 100644 tools/testing/selftests/bpf/prog_tests/icmp_send_unreach_kfunc.c\n create mode 100644 tools/testing/selftests/bpf/progs/icmp_send_unreach.c\n\n--\n2.34.1"}