=== Context ===
In the context of a middlebox, fragmented packets are tricky to handle. The full 5-tuple of a packet is often only available in the first fragment which makes enforcing consistent policy difficult. There are really only two stateless options, neither of which are very nice:
1. Enforce policy on first fragment and accept all subsequent fragments. This works but may let in certain attacks or allow data exfiltration.
2. Enforce policy on first fragment and drop all subsequent fragments. This does not really work b/c some protocols may rely on fragmentation. For example, DNS may rely on oversized UDP packets for large responses.
So stateful tracking is the only sane option. RFC 8900 [0] calls this out as well in section 6.3:
Middleboxes [...] should process IP fragments in a manner that is consistent with [RFC0791] and [RFC8200]. In many cases, middleboxes must maintain state in order to achieve this goal.
=== BPF related bits ===
Policy has traditionally been enforced from XDP/TC hooks. Both hooks run before kernel reassembly facilities. However, with the new BPF_PROG_TYPE_NETFILTER, we can rather easily hook into existing netfilter reassembly infra.
The basic idea is we bump a refcnt on the netfilter defrag module and then run the bpf prog after the defrag module runs. This allows bpf progs to transparently see full, reassembled packets. The nice thing about this is that progs don't have to carry around logic to detect fragments.
=== Patchset details ===
There was an earlier attempt at providing defrag via kfuncs [1]. The feedback was that we could end up doing too much stuff in prog execution context (like sending ICMP error replies). However, I think there are still some outstanding discussion w.r.t. performance when it comes to netfilter vs the previous approach. I'll schedule some time during office hours for this.
Patches 1 & 2 are stolenfrom Florian. Hopefully he doesn't mind. There were some outstanding comments on the v2 [2] but it doesn't look like a v3 was ever submitted. I've addressed the comments and put them in this patchset cuz I needed them.
Finally, the new selftest seems to be a little flaky. I'm not quite sure why the server will fail to `recvfrom()` occassionaly. I'm fairly sure it's a timing related issue with creating veths. I'll keep debugging but I didn't want that to hold up discussion on this patchset.
[0]: https://datatracker.ietf.org/doc/html/rfc8900 [1]: https://lore.kernel.org/bpf/cover.1677526810.git.dxu@dxuuu.xyz/ [2]: https://lore.kernel.org/bpf/20230525110100.8212-1-fw@strlen.de/
Daniel Xu (7): tools: libbpf: add netfilter link attach helper selftests/bpf: Add bpf_program__attach_netfilter helper test netfilter: defrag: Add glue hooks for enabling/disabling defrag netfilter: bpf: Support BPF_F_NETFILTER_IP_DEFRAG in netfilter link bpf: selftests: Support not connecting client socket bpf: selftests: Support custom type and proto for client sockets bpf: selftests: Add defrag selftests
include/linux/netfilter.h | 12 + include/uapi/linux/bpf.h | 5 + net/ipv4/netfilter/nf_defrag_ipv4.c | 8 + net/ipv6/netfilter/nf_defrag_ipv6_hooks.c | 10 + net/netfilter/core.c | 6 + net/netfilter/nf_bpf_link.c | 108 ++++++- tools/include/uapi/linux/bpf.h | 5 + tools/lib/bpf/bpf.c | 8 + tools/lib/bpf/bpf.h | 6 + tools/lib/bpf/libbpf.c | 47 +++ tools/lib/bpf/libbpf.h | 15 + tools/lib/bpf/libbpf.map | 1 + tools/testing/selftests/bpf/Makefile | 4 +- .../selftests/bpf/generate_udp_fragments.py | 90 ++++++ .../selftests/bpf/ip_check_defrag_frags.h | 57 ++++ tools/testing/selftests/bpf/network_helpers.c | 26 +- tools/testing/selftests/bpf/network_helpers.h | 3 + .../bpf/prog_tests/ip_check_defrag.c | 282 ++++++++++++++++++ .../bpf/prog_tests/netfilter_basic.c | 78 +++++ .../selftests/bpf/progs/ip_check_defrag.c | 104 +++++++ .../bpf/progs/test_netfilter_link_attach.c | 14 + 21 files changed, 868 insertions(+), 21 deletions(-) create mode 100755 tools/testing/selftests/bpf/generate_udp_fragments.py create mode 100644 tools/testing/selftests/bpf/ip_check_defrag_frags.h create mode 100644 tools/testing/selftests/bpf/prog_tests/ip_check_defrag.c create mode 100644 tools/testing/selftests/bpf/prog_tests/netfilter_basic.c create mode 100644 tools/testing/selftests/bpf/progs/ip_check_defrag.c create mode 100644 tools/testing/selftests/bpf/progs/test_netfilter_link_attach.c
Call bpf_program__attach_netfilter() with different protocol/hook/priority combinations.
Test fails if supposedly-illegal attachments work (e.g., bogus protocol family, illegal priority and so on) or if a should-work attachment fails.
Co-developed-by: Florian Westphal fw@strlen.de Signed-off-by: Florian Westphal fw@strlen.de Signed-off-by: Daniel Xu dxu@dxuuu.xyz --- .../bpf/prog_tests/netfilter_basic.c | 78 +++++++++++++++++++ .../bpf/progs/test_netfilter_link_attach.c | 14 ++++ 2 files changed, 92 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/netfilter_basic.c create mode 100644 tools/testing/selftests/bpf/progs/test_netfilter_link_attach.c
diff --git a/tools/testing/selftests/bpf/prog_tests/netfilter_basic.c b/tools/testing/selftests/bpf/prog_tests/netfilter_basic.c new file mode 100644 index 000000000000..357353fee19d --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/netfilter_basic.c @@ -0,0 +1,78 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#include <netinet/in.h> +#include <linux/netfilter.h> + +#include "test_progs.h" +#include "test_netfilter_link_attach.skel.h" + +struct nf_hook_options { + __u32 pf; + __u32 hooknum; + __s32 priority; + __u32 flags; + + bool expect_success; +}; + +struct nf_hook_options nf_hook_attach_tests[] = { + { }, + { .pf = NFPROTO_NUMPROTO, }, + { .pf = NFPROTO_IPV4, .hooknum = 42, }, + { .pf = NFPROTO_IPV4, .priority = INT_MIN }, + { .pf = NFPROTO_IPV4, .priority = INT_MAX }, + { .pf = NFPROTO_IPV4, .flags = UINT_MAX }, + + { .pf = NFPROTO_INET, .priority = 1, }, + + { .pf = NFPROTO_IPV4, .priority = -10000, .expect_success = true }, + { .pf = NFPROTO_IPV6, .priority = 10001, .expect_success = true }, +}; + +void test_netfilter_basic(void) +{ + struct test_netfilter_link_attach *skel; + LIBBPF_OPTS(bpf_netfilter_opts, opts); + struct bpf_program *prog; + int i; + + skel = test_netfilter_link_attach__open_and_load(); + if (!ASSERT_OK_PTR(skel, "test_netfilter_link_attach__open_and_load")) + goto out; + + prog = skel->progs.nf_link_attach_test; + + for (i = 0; i < ARRAY_SIZE(nf_hook_attach_tests); i++) { + struct bpf_link *link; + +#define X(opts, m, i) opts.m = nf_hook_attach_tests[(i)].m + X(opts, pf, i); + X(opts, hooknum, i); + X(opts, priority, i); + X(opts, flags, i); +#undef X + link = bpf_program__attach_netfilter(prog, &opts); + if (nf_hook_attach_tests[i].expect_success) { + struct bpf_link *link2; + + if (!ASSERT_OK_PTR(link, "program attach successful")) + continue; + + link2 = bpf_program__attach_netfilter(prog, &opts); + ASSERT_ERR_PTR(link2, "attach program with same pf/hook/priority"); + + if (!ASSERT_OK(bpf_link__destroy(link), "link destroy")) + break; + + link2 = bpf_program__attach_netfilter(prog, &opts); + if (!ASSERT_OK_PTR(link2, "program reattach successful")) + continue; + if (!ASSERT_OK(bpf_link__destroy(link2), "link destroy")) + break; + } else { + ASSERT_ERR_PTR(link, "program load failure"); + } + } +out: + test_netfilter_link_attach__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/test_netfilter_link_attach.c b/tools/testing/selftests/bpf/progs/test_netfilter_link_attach.c new file mode 100644 index 000000000000..03a475160abe --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_netfilter_link_attach.c @@ -0,0 +1,14 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#include "vmlinux.h" +#include <bpf/bpf_helpers.h> + +#define NF_ACCEPT 1 + +SEC("netfilter") +int nf_link_attach_test(struct bpf_nf_ctx *ctx) +{ + return NF_ACCEPT; +} + +char _license[] SEC("license") = "GPL";
For connectionless protocols or raw sockets we do not want to actually connect() to the server.
Signed-off-by: Daniel Xu dxu@dxuuu.xyz --- tools/testing/selftests/bpf/network_helpers.c | 5 +++-- tools/testing/selftests/bpf/network_helpers.h | 1 + 2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/bpf/network_helpers.c b/tools/testing/selftests/bpf/network_helpers.c index a105c0cd008a..d5c78c08903b 100644 --- a/tools/testing/selftests/bpf/network_helpers.c +++ b/tools/testing/selftests/bpf/network_helpers.c @@ -301,8 +301,9 @@ int connect_to_fd_opts(int server_fd, const struct network_helper_opts *opts) strlen(opts->cc) + 1)) goto error_close;
- if (connect_fd_to_addr(fd, &addr, addrlen, opts->must_fail)) - goto error_close; + if (!opts->noconnect) + if (connect_fd_to_addr(fd, &addr, addrlen, opts->must_fail)) + goto error_close;
return fd;
diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h index 694185644da6..87894dc984dd 100644 --- a/tools/testing/selftests/bpf/network_helpers.h +++ b/tools/testing/selftests/bpf/network_helpers.h @@ -21,6 +21,7 @@ struct network_helper_opts { const char *cc; int timeout_ms; bool must_fail; + bool noconnect; };
/* ipv4 test vector */
Extend connect_to_fd_opts() to take optional type and protocol parameters for the client socket. These parameters are useful when opening a raw socket to send IP fragments.
Signed-off-by: Daniel Xu dxu@dxuuu.xyz --- tools/testing/selftests/bpf/network_helpers.c | 21 +++++++++++++------ tools/testing/selftests/bpf/network_helpers.h | 2 ++ 2 files changed, 17 insertions(+), 6 deletions(-)
diff --git a/tools/testing/selftests/bpf/network_helpers.c b/tools/testing/selftests/bpf/network_helpers.c index d5c78c08903b..910d5d0470e6 100644 --- a/tools/testing/selftests/bpf/network_helpers.c +++ b/tools/testing/selftests/bpf/network_helpers.c @@ -270,14 +270,23 @@ int connect_to_fd_opts(int server_fd, const struct network_helper_opts *opts) opts = &default_opts;
optlen = sizeof(type); - if (getsockopt(server_fd, SOL_SOCKET, SO_TYPE, &type, &optlen)) { - log_err("getsockopt(SOL_TYPE)"); - return -1; + + if (opts->type) { + type = opts->type; + } else { + if (getsockopt(server_fd, SOL_SOCKET, SO_TYPE, &type, &optlen)) { + log_err("getsockopt(SOL_TYPE)"); + return -1; + } }
- if (getsockopt(server_fd, SOL_SOCKET, SO_PROTOCOL, &protocol, &optlen)) { - log_err("getsockopt(SOL_PROTOCOL)"); - return -1; + if (opts->proto) { + protocol = opts->proto; + } else { + if (getsockopt(server_fd, SOL_SOCKET, SO_PROTOCOL, &protocol, &optlen)) { + log_err("getsockopt(SOL_PROTOCOL)"); + return -1; + } }
addrlen = sizeof(addr); diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h index 87894dc984dd..5eccc67d1a99 100644 --- a/tools/testing/selftests/bpf/network_helpers.h +++ b/tools/testing/selftests/bpf/network_helpers.h @@ -22,6 +22,8 @@ struct network_helper_opts { int timeout_ms; bool must_fail; bool noconnect; + int type; + int proto; };
/* ipv4 test vector */
These selftests tests 2 major scenarios: the BPF based defragmentation can successfully be done and that packet pointers are invalidated after calls to the kfunc. The logic is similar for both ipv4 and ipv6.
In the first scenario, we create a UDP client and UDP echo server. The the server side is fairly straightforward: we attach the prog and simply echo back the message.
The on the client side, we send fragmented packets to and expect the reassembled message back from the server.
Signed-off-by: Daniel Xu dxu@dxuuu.xyz --- tools/testing/selftests/bpf/Makefile | 4 +- .../selftests/bpf/generate_udp_fragments.py | 90 ++++++ .../selftests/bpf/ip_check_defrag_frags.h | 57 ++++ .../bpf/prog_tests/ip_check_defrag.c | 282 ++++++++++++++++++ .../selftests/bpf/progs/ip_check_defrag.c | 104 +++++++ 5 files changed, 535 insertions(+), 2 deletions(-) create mode 100755 tools/testing/selftests/bpf/generate_udp_fragments.py create mode 100644 tools/testing/selftests/bpf/ip_check_defrag_frags.h create mode 100644 tools/testing/selftests/bpf/prog_tests/ip_check_defrag.c create mode 100644 tools/testing/selftests/bpf/progs/ip_check_defrag.c
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 538df8fb8c42..b47f20381d56 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -561,8 +561,8 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c \ network_helpers.c testing_helpers.c \ btf_helpers.c flow_dissector_load.h \ cap_helpers.c test_loader.c xsk.c disasm.c \ - json_writer.c unpriv_helpers.c - + json_writer.c unpriv_helpers.c \ + ip_check_defrag_frags.h TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko \ $(OUTPUT)/liburandom_read.so \ $(OUTPUT)/xdp_synproxy \ diff --git a/tools/testing/selftests/bpf/generate_udp_fragments.py b/tools/testing/selftests/bpf/generate_udp_fragments.py new file mode 100755 index 000000000000..2b8a1187991c --- /dev/null +++ b/tools/testing/selftests/bpf/generate_udp_fragments.py @@ -0,0 +1,90 @@ +#!/bin/env python3 +# SPDX-License-Identifier: GPL-2.0 + +""" +This script helps generate fragmented UDP packets. + +While it is technically possible to dynamically generate +fragmented packets in C, it is much harder to read and write +said code. `scapy` is relatively industry standard and really +easy to read / write. + +So we choose to write this script that generates a valid C +header. Rerun script and commit generated file after any +modifications. +""" + +import argparse +import os + +from scapy.all import * + + +# These constants must stay in sync with `ip_check_defrag.c` +VETH1_ADDR = "172.16.1.200" +VETH0_ADDR6 = "fc00::100" +VETH1_ADDR6 = "fc00::200" +CLIENT_PORT = 48878 +SERVER_PORT = 48879 +MAGIC_MESSAGE = "THIS IS THE ORIGINAL MESSAGE, PLEASE REASSEMBLE ME" + + +def print_header(f): + f.write("// SPDX-License-Identifier: GPL-2.0\n") + f.write("/* DO NOT EDIT -- this file is generated */\n") + f.write("\n") + f.write("#ifndef _IP_CHECK_DEFRAG_FRAGS_H\n") + f.write("#define _IP_CHECK_DEFRAG_FRAGS_H\n") + f.write("\n") + f.write("#include <stdint.h>\n") + f.write("\n") + + +def print_frags(f, frags, v6): + for idx, frag in enumerate(frags): + # 10 bytes per line to keep width in check + chunks = [frag[i : i + 10] for i in range(0, len(frag), 10)] + chunks_fmted = [", ".join([str(hex(b)) for b in chunk]) for chunk in chunks] + suffix = "6" if v6 else "" + + f.write(f"static uint8_t frag{suffix}_{idx}[] = {{\n") + for chunk in chunks_fmted: + f.write(f"\t{chunk},\n") + f.write(f"}};\n") + + +def print_trailer(f): + f.write("\n") + f.write("#endif /* _IP_CHECK_DEFRAG_FRAGS_H */\n") + + +def main(f): + # srcip of 0 is filled in by IP_HDRINCL + sip = "0.0.0.0" + sip6 = VETH0_ADDR6 + dip = VETH1_ADDR + dip6 = VETH1_ADDR6 + sport = CLIENT_PORT + dport = SERVER_PORT + payload = MAGIC_MESSAGE.encode() + + # Disable UDPv4 checksums to keep code simpler + pkt = IP(src=sip,dst=dip) / UDP(sport=sport,dport=dport,chksum=0) / Raw(load=payload) + # UDPv6 requires a checksum + # Also pin the ipv6 fragment header ID, otherwise it's a random value + pkt6 = IPv6(src=sip6,dst=dip6) / IPv6ExtHdrFragment(id=0xBEEF) / UDP(sport=sport,dport=dport) / Raw(load=payload) + + frags = [f.build() for f in pkt.fragment(24)] + frags6 = [f.build() for f in fragment6(pkt6, 72)] + + print_header(f) + print_frags(f, frags, False) + print_frags(f, frags6, True) + print_trailer(f) + + +if __name__ == "__main__": + dir = os.path.dirname(os.path.realpath(__file__)) + header = f"{dir}/ip_check_defrag_frags.h" + with open(header, "w") as f: + main(f) diff --git a/tools/testing/selftests/bpf/ip_check_defrag_frags.h b/tools/testing/selftests/bpf/ip_check_defrag_frags.h new file mode 100644 index 000000000000..70ab7e9fa22b --- /dev/null +++ b/tools/testing/selftests/bpf/ip_check_defrag_frags.h @@ -0,0 +1,57 @@ +// SPDX-License-Identifier: GPL-2.0 +/* DO NOT EDIT -- this file is generated */ + +#ifndef _IP_CHECK_DEFRAG_FRAGS_H +#define _IP_CHECK_DEFRAG_FRAGS_H + +#include <stdint.h> + +static uint8_t frag_0[] = { + 0x45, 0x0, 0x0, 0x2c, 0x0, 0x1, 0x20, 0x0, 0x40, 0x11, + 0xac, 0xe8, 0x0, 0x0, 0x0, 0x0, 0xac, 0x10, 0x1, 0xc8, + 0xbe, 0xee, 0xbe, 0xef, 0x0, 0x3a, 0x0, 0x0, 0x54, 0x48, + 0x49, 0x53, 0x20, 0x49, 0x53, 0x20, 0x54, 0x48, 0x45, 0x20, + 0x4f, 0x52, 0x49, 0x47, +}; +static uint8_t frag_1[] = { + 0x45, 0x0, 0x0, 0x2c, 0x0, 0x1, 0x20, 0x3, 0x40, 0x11, + 0xac, 0xe5, 0x0, 0x0, 0x0, 0x0, 0xac, 0x10, 0x1, 0xc8, + 0x49, 0x4e, 0x41, 0x4c, 0x20, 0x4d, 0x45, 0x53, 0x53, 0x41, + 0x47, 0x45, 0x2c, 0x20, 0x50, 0x4c, 0x45, 0x41, 0x53, 0x45, + 0x20, 0x52, 0x45, 0x41, +}; +static uint8_t frag_2[] = { + 0x45, 0x0, 0x0, 0x1e, 0x0, 0x1, 0x0, 0x6, 0x40, 0x11, + 0xcc, 0xf0, 0x0, 0x0, 0x0, 0x0, 0xac, 0x10, 0x1, 0xc8, + 0x53, 0x53, 0x45, 0x4d, 0x42, 0x4c, 0x45, 0x20, 0x4d, 0x45, +}; +static uint8_t frag6_0[] = { + 0x60, 0x0, 0x0, 0x0, 0x0, 0x20, 0x2c, 0x40, 0xfc, 0x0, + 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, + 0x0, 0x0, 0x1, 0x0, 0xfc, 0x0, 0x0, 0x0, 0x0, 0x0, + 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2, 0x0, + 0x11, 0x0, 0x0, 0x1, 0x0, 0x0, 0xbe, 0xef, 0xbe, 0xee, + 0xbe, 0xef, 0x0, 0x3a, 0xd0, 0xf8, 0x54, 0x48, 0x49, 0x53, + 0x20, 0x49, 0x53, 0x20, 0x54, 0x48, 0x45, 0x20, 0x4f, 0x52, + 0x49, 0x47, +}; +static uint8_t frag6_1[] = { + 0x60, 0x0, 0x0, 0x0, 0x0, 0x20, 0x2c, 0x40, 0xfc, 0x0, + 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, + 0x0, 0x0, 0x1, 0x0, 0xfc, 0x0, 0x0, 0x0, 0x0, 0x0, + 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2, 0x0, + 0x11, 0x0, 0x0, 0x19, 0x0, 0x0, 0xbe, 0xef, 0x49, 0x4e, + 0x41, 0x4c, 0x20, 0x4d, 0x45, 0x53, 0x53, 0x41, 0x47, 0x45, + 0x2c, 0x20, 0x50, 0x4c, 0x45, 0x41, 0x53, 0x45, 0x20, 0x52, + 0x45, 0x41, +}; +static uint8_t frag6_2[] = { + 0x60, 0x0, 0x0, 0x0, 0x0, 0x12, 0x2c, 0x40, 0xfc, 0x0, + 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, + 0x0, 0x0, 0x1, 0x0, 0xfc, 0x0, 0x0, 0x0, 0x0, 0x0, + 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2, 0x0, + 0x11, 0x0, 0x0, 0x30, 0x0, 0x0, 0xbe, 0xef, 0x53, 0x53, + 0x45, 0x4d, 0x42, 0x4c, 0x45, 0x20, 0x4d, 0x45, +}; + +#endif /* _IP_CHECK_DEFRAG_FRAGS_H */ diff --git a/tools/testing/selftests/bpf/prog_tests/ip_check_defrag.c b/tools/testing/selftests/bpf/prog_tests/ip_check_defrag.c new file mode 100644 index 000000000000..5cd08d6e0ebc --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/ip_check_defrag.c @@ -0,0 +1,282 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <test_progs.h> +#include <net/if.h> +#include <linux/netfilter.h> +#include <network_helpers.h> +#include "ip_check_defrag.skel.h" +#include "ip_check_defrag_frags.h" + +/* + * This selftest spins up a client and an echo server, each in their own + * network namespace. The client will send a fragmented message to the server. + * The prog attached to the server will shoot down any fragments. Thus, if + * the server is able to correctly echo back the message to the client, we will + * have verified that netfilter is reassembling packets for us. + * + * Topology: + * ========= + * NS0 | NS1 + * | + * client | server + * ---------- | ---------- + * | veth0 | --------- | veth1 | + * ---------- peer ---------- + * | + * | with bpf + */ + +#define NS0 "defrag_ns0" +#define NS1 "defrag_ns1" +#define VETH0 "veth0" +#define VETH1 "veth1" +#define VETH0_ADDR "172.16.1.100" +#define VETH0_ADDR6 "fc00::100" +/* The following constants must stay in sync with `generate_udp_fragments.py` */ +#define VETH1_ADDR "172.16.1.200" +#define VETH1_ADDR6 "fc00::200" +#define CLIENT_PORT 48878 +#define SERVER_PORT 48879 +#define MAGIC_MESSAGE "THIS IS THE ORIGINAL MESSAGE, PLEASE REASSEMBLE ME" + +static int setup_topology(bool ipv6) +{ + bool up; + int i; + + SYS(fail, "ip netns add " NS0); + SYS(fail, "ip netns add " NS1); + SYS(fail, "ip link add " VETH0 " netns " NS0 " type veth peer name " VETH1 " netns " NS1); + if (ipv6) { + SYS(fail, "ip -6 -net " NS0 " addr add " VETH0_ADDR6 "/64 dev " VETH0 " nodad"); + SYS(fail, "ip -6 -net " NS1 " addr add " VETH1_ADDR6 "/64 dev " VETH1 " nodad"); + } else { + SYS(fail, "ip -net " NS0 " addr add " VETH0_ADDR "/24 dev " VETH0); + SYS(fail, "ip -net " NS1 " addr add " VETH1_ADDR "/24 dev " VETH1); + } + SYS(fail, "ip -net " NS0 " link set dev " VETH0 " up"); + SYS(fail, "ip -net " NS1 " link set dev " VETH1 " up"); + + /* Wait for up to 5s for links to come up */ + for (i = 0; i < 5; ++i) { + if (ipv6) + up = !system("ip netns exec " NS0 " ping -6 -c 1 -W 1 " VETH1_ADDR6 " &>/dev/null"); + else + up = !system("ip netns exec " NS0 " ping -c 1 -W 1 " VETH1_ADDR " &>/dev/null"); + + if (up) + break; + } + + return 0; +fail: + return -1; +} + +static void cleanup_topology(void) +{ + SYS_NOFAIL("test -f /var/run/netns/" NS0 " && ip netns delete " NS0); + SYS_NOFAIL("test -f /var/run/netns/" NS1 " && ip netns delete " NS1); +} + +static int attach(struct ip_check_defrag *skel, bool ipv6) +{ + LIBBPF_OPTS(bpf_netfilter_opts, opts, + .pf = ipv6 ? NFPROTO_IPV6 : NFPROTO_IPV4, + .priority = 42, + .flags = BPF_F_NETFILTER_IP_DEFRAG); + struct nstoken *nstoken; + int err = -1; + + nstoken = open_netns(NS1); + + skel->links.defrag = bpf_program__attach_netfilter(skel->progs.defrag, &opts); + if (!ASSERT_OK_PTR(skel->links.defrag, "program attach")) + goto out; + + err = 0; +out: + close_netns(nstoken); + return err; +} + +static int send_frags(int client) +{ + struct sockaddr_storage saddr; + struct sockaddr *saddr_p; + socklen_t saddr_len; + int err; + + saddr_p = (struct sockaddr *)&saddr; + err = make_sockaddr(AF_INET, VETH1_ADDR, SERVER_PORT, &saddr, &saddr_len); + if (!ASSERT_OK(err, "make_sockaddr")) + return -1; + + err = sendto(client, frag_0, sizeof(frag_0), 0, saddr_p, saddr_len); + if (!ASSERT_GE(err, 0, "sendto frag_0")) + return -1; + + err = sendto(client, frag_1, sizeof(frag_1), 0, saddr_p, saddr_len); + if (!ASSERT_GE(err, 0, "sendto frag_1")) + return -1; + + err = sendto(client, frag_2, sizeof(frag_2), 0, saddr_p, saddr_len); + if (!ASSERT_GE(err, 0, "sendto frag_2")) + return -1; + + return 0; +} + +static int send_frags6(int client) +{ + struct sockaddr_storage saddr; + struct sockaddr *saddr_p; + socklen_t saddr_len; + int err; + + saddr_p = (struct sockaddr *)&saddr; + /* Port needs to be set to 0 for raw ipv6 socket for some reason */ + err = make_sockaddr(AF_INET6, VETH1_ADDR6, 0, &saddr, &saddr_len); + if (!ASSERT_OK(err, "make_sockaddr")) + return -1; + + err = sendto(client, frag6_0, sizeof(frag6_0), 0, saddr_p, saddr_len); + if (!ASSERT_GE(err, 0, "sendto frag6_0")) + return -1; + + err = sendto(client, frag6_1, sizeof(frag6_1), 0, saddr_p, saddr_len); + if (!ASSERT_GE(err, 0, "sendto frag6_1")) + return -1; + + err = sendto(client, frag6_2, sizeof(frag6_2), 0, saddr_p, saddr_len); + if (!ASSERT_GE(err, 0, "sendto frag6_2")) + return -1; + + return 0; +} + +void test_bpf_ip_check_defrag_ok(bool ipv6) +{ + struct network_helper_opts rx_opts = { + .timeout_ms = 1000, + .noconnect = true, + }; + struct network_helper_opts tx_ops = { + .timeout_ms = 1000, + .type = SOCK_RAW, + .proto = IPPROTO_RAW, + .noconnect = true, + }; + struct sockaddr_storage caddr; + struct ip_check_defrag *skel; + struct nstoken *nstoken; + int client_tx_fd = -1; + int client_rx_fd = -1; + socklen_t caddr_len; + int srv_fd = -1; + char buf[1024]; + int len, err; + + skel = ip_check_defrag__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel_open")) + return; + + if (!ASSERT_OK(setup_topology(ipv6), "setup_topology")) + goto out; + + if (!ASSERT_OK(attach(skel, ipv6), "attach")) + goto out; + + /* Start server in ns1 */ + nstoken = open_netns(NS1); + if (!ASSERT_OK_PTR(nstoken, "setns ns1")) + goto out; + srv_fd = start_server(ipv6 ? AF_INET6 : AF_INET, SOCK_DGRAM, NULL, SERVER_PORT, 0); + close_netns(nstoken); + if (!ASSERT_GE(srv_fd, 0, "start_server")) + goto out; + + /* Open tx raw socket in ns0 */ + nstoken = open_netns(NS0); + if (!ASSERT_OK_PTR(nstoken, "setns ns0")) + goto out; + client_tx_fd = connect_to_fd_opts(srv_fd, &tx_ops); + close_netns(nstoken); + if (!ASSERT_GE(client_tx_fd, 0, "connect_to_fd_opts")) + goto out; + + /* Open rx socket in ns0 */ + nstoken = open_netns(NS0); + if (!ASSERT_OK_PTR(nstoken, "setns ns0")) + goto out; + client_rx_fd = connect_to_fd_opts(srv_fd, &rx_opts); + close_netns(nstoken); + if (!ASSERT_GE(client_rx_fd, 0, "connect_to_fd_opts")) + goto out; + + /* Bind rx socket to a premeditated port */ + memset(&caddr, 0, sizeof(caddr)); + nstoken = open_netns(NS0); + if (!ASSERT_OK_PTR(nstoken, "setns ns0")) + goto out; + if (ipv6) { + struct sockaddr_in6 *c = (struct sockaddr_in6 *)&caddr; + + c->sin6_family = AF_INET6; + inet_pton(AF_INET6, VETH0_ADDR6, &c->sin6_addr); + c->sin6_port = htons(CLIENT_PORT); + err = bind(client_rx_fd, (struct sockaddr *)c, sizeof(*c)); + } else { + struct sockaddr_in *c = (struct sockaddr_in *)&caddr; + + c->sin_family = AF_INET; + inet_pton(AF_INET, VETH0_ADDR, &c->sin_addr); + c->sin_port = htons(CLIENT_PORT); + err = bind(client_rx_fd, (struct sockaddr *)c, sizeof(*c)); + } + close_netns(nstoken); + if (!ASSERT_OK(err, "bind")) + goto out; + + /* Send message in fragments */ + if (ipv6) { + if (!ASSERT_OK(send_frags6(client_tx_fd), "send_frags6")) + goto out; + } else { + if (!ASSERT_OK(send_frags(client_tx_fd), "send_frags")) + goto out; + } + + if (!ASSERT_EQ(skel->bss->shootdowns, 0, "shootdowns")) + goto out; + + /* Receive reassembled msg on server and echo back to client */ + len = recvfrom(srv_fd, buf, sizeof(buf), 0, (struct sockaddr *)&caddr, &caddr_len); + if (!ASSERT_GE(len, 0, "server recvfrom")) + goto out; + len = sendto(srv_fd, buf, len, 0, (struct sockaddr *)&caddr, caddr_len); + if (!ASSERT_GE(len, 0, "server sendto")) + goto out; + + /* Expect reassembed message to be echoed back */ + len = recvfrom(client_rx_fd, buf, sizeof(buf), 0, NULL, NULL); + if (!ASSERT_EQ(len, sizeof(MAGIC_MESSAGE) - 1, "client short read")) + goto out; + +out: + if (client_rx_fd != -1) + close(client_rx_fd); + if (client_tx_fd != -1) + close(client_tx_fd); + if (srv_fd != -1) + close(srv_fd); + cleanup_topology(); + ip_check_defrag__destroy(skel); +} + +void test_bpf_ip_check_defrag(void) +{ + if (test__start_subtest("v4")) + test_bpf_ip_check_defrag_ok(false); + if (test__start_subtest("v6")) + test_bpf_ip_check_defrag_ok(true); +} diff --git a/tools/testing/selftests/bpf/progs/ip_check_defrag.c b/tools/testing/selftests/bpf/progs/ip_check_defrag.c new file mode 100644 index 000000000000..4259c6d59968 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/ip_check_defrag.c @@ -0,0 +1,104 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include "vmlinux.h" +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_endian.h> +#include "bpf_tracing_net.h" + +#define NF_DROP 0 +#define NF_ACCEPT 1 +#define ETH_P_IP 0x0800 +#define ETH_P_IPV6 0x86DD +#define IP_MF 0x2000 +#define IP_OFFSET 0x1FFF +#define NEXTHDR_FRAGMENT 44 + +extern int bpf_dynptr_from_skb(struct sk_buff *skb, __u64 flags, + struct bpf_dynptr *ptr__uninit) __ksym; +extern void *bpf_dynptr_slice(const struct bpf_dynptr *ptr, uint32_t offset, + void *buffer, uint32_t buffer__sz) __ksym; + +volatile int shootdowns = 0; + +static bool is_frag_v4(struct iphdr *iph) +{ + int offset; + int flags; + + offset = bpf_ntohs(iph->frag_off); + flags = offset & ~IP_OFFSET; + offset &= IP_OFFSET; + offset <<= 3; + + return (flags & IP_MF) || offset; +} + +static bool is_frag_v6(struct ipv6hdr *ip6h) +{ + /* Simplifying assumption that there are no extension headers + * between fixed header and fragmentation header. This assumption + * is only valid in this test case. It saves us the hassle of + * searching all potential extension headers. + */ + return ip6h->nexthdr == NEXTHDR_FRAGMENT; +} + +static int handle_v4(struct sk_buff *skb) +{ + struct bpf_dynptr ptr; + u8 iph_buf[20] = {}; + struct iphdr *iph; + + if (bpf_dynptr_from_skb(skb, 0, &ptr)) + return NF_DROP; + + iph = bpf_dynptr_slice(&ptr, 0, iph_buf, sizeof(iph_buf)); + if (!iph) + return NF_DROP; + + /* Shootdown any frags */ + if (is_frag_v4(iph)) { + shootdowns++; + return NF_DROP; + } + + return NF_ACCEPT; +} + +static int handle_v6(struct sk_buff *skb) +{ + struct bpf_dynptr ptr; + struct ipv6hdr *ip6h; + u8 ip6h_buf[40] = {}; + + if (bpf_dynptr_from_skb(skb, 0, &ptr)) + return NF_DROP; + + ip6h = bpf_dynptr_slice(&ptr, 0, ip6h_buf, sizeof(ip6h_buf)); + if (!ip6h) + return NF_DROP; + + /* Shootdown any frags */ + if (is_frag_v6(ip6h)) { + shootdowns++; + return NF_DROP; + } + + return NF_ACCEPT; +} + +SEC("netfilter") +int defrag(struct bpf_nf_ctx *ctx) +{ + struct sk_buff *skb = ctx->skb; + + switch (bpf_ntohs(skb->protocol)) { + case ETH_P_IP: + return handle_v4(skb); + case ETH_P_IPV6: + return handle_v6(skb); + default: + return NF_ACCEPT; + } +} + +char _license[] SEC("license") = "GPL";
Daniel Xu dxu@dxuuu.xyz wrote:
Patches 1 & 2 are stolenfrom Florian. Hopefully he doesn't mind. There were some outstanding comments on the v2 [2] but it doesn't look like a v3 was ever submitted. I've addressed the comments and put them in this patchset cuz I needed them.
I did not submit a v3 because i had to wait for the bpf -> bpf-next merge to get "bpf: netfilter: Add BPF_NETFILTER bpf_attach_type".
Now that has been done so I will do v3 shortly.
Hi Florian,
On Tue, Jun 27, 2023 at 12:48:20PM +0200, Florian Westphal wrote:
Daniel Xu dxu@dxuuu.xyz wrote:
Patches 1 & 2 are stolenfrom Florian. Hopefully he doesn't mind. There were some outstanding comments on the v2 [2] but it doesn't look like a v3 was ever submitted. I've addressed the comments and put them in this patchset cuz I needed them.
I did not submit a v3 because i had to wait for the bpf -> bpf-next merge to get "bpf: netfilter: Add BPF_NETFILTER bpf_attach_type".
Now that has been done so I will do v3 shortly.
Ack. Will wait for your patches to go in before sending my v2.
Thanks, Daniel
The basic idea is we bump a refcnt on the netfilter defrag module and then run the bpf prog after the defrag module runs. This allows bpf progs to transparently see full, reassembled packets. The nice thing about this is that progs don't have to carry around logic to detect fragments.
One high-level comment after glancing through the series: Instead of allocating a flag specifically for the defrag module, why not support loading (and holding) arbitrary netfilter modules in the UAPI? If we need to allocate a new flag every time someone wants to use a netfilter module along with BPF we'll run out of flags pretty quickly :)
-Toke
Hi Toke,
Thanks for taking a look at the patchset.
On Tue, Jun 27, 2023 at 04:25:13PM +0200, Toke Høiland-Jørgensen wrote:
The basic idea is we bump a refcnt on the netfilter defrag module and then run the bpf prog after the defrag module runs. This allows bpf progs to transparently see full, reassembled packets. The nice thing about this is that progs don't have to carry around logic to detect fragments.
One high-level comment after glancing through the series: Instead of allocating a flag specifically for the defrag module, why not support loading (and holding) arbitrary netfilter modules in the UAPI? If we need to allocate a new flag every time someone wants to use a netfilter module along with BPF we'll run out of flags pretty quickly :)
I don't have enough context on netfilter in general to say if it'd be generically useful -- perhaps Florian can comment on that.
However, I'm not sure such a mechanism removes the need for a flag. The netfilter defrag modules still need to be called into to bump the refcnt.
The module could export some kfuncs to inc/dec the refcnt, but it'd be rather odd for prog code to think about the lifetime of the attachment (as inc/dec for _each_ prog execution seems wasteful and slow). AFAIK all the other resource acquire/release APIs are for a single prog execution.
So a flag for link attach feels the most natural to me. We could always add a flag2 field or something right?
[...]
Thanks, Daniel
Toke Høiland-Jørgensen toke@redhat.com wrote:
The basic idea is we bump a refcnt on the netfilter defrag module and then run the bpf prog after the defrag module runs. This allows bpf progs to transparently see full, reassembled packets. The nice thing about this is that progs don't have to carry around logic to detect fragments.
One high-level comment after glancing through the series: Instead of allocating a flag specifically for the defrag module, why not support loading (and holding) arbitrary netfilter modules in the UAPI?
How would that work/look like?
defrag (and conntrack) need special handling because loading these modules has no effect on the datapath.
Traditionally, yes, loading was enough, but now with netns being ubiquitous we don't want these to get enabled unless needed.
Ignoring bpf, this happens when user adds nftables/iptables rules that check for conntrack state, use some form of NAT or use e.g. tproxy.
For bpf a flag during link attachment seemed like the best way to go.
At the moment I only see two flags for this, namely "need defrag" and "need conntrack".
For conntrack, we MIGHT be able to not need a flag but maybe verifier could "guess" based on kfuncs used.
But for defrag, I don't think its good to add a dummy do-nothing kfunc just for expressing the dependency on bpf prog side.
Florian Westphal fw@strlen.de writes:
Toke Høiland-Jørgensen toke@redhat.com wrote:
The basic idea is we bump a refcnt on the netfilter defrag module and then run the bpf prog after the defrag module runs. This allows bpf progs to transparently see full, reassembled packets. The nice thing about this is that progs don't have to carry around logic to detect fragments.
One high-level comment after glancing through the series: Instead of allocating a flag specifically for the defrag module, why not support loading (and holding) arbitrary netfilter modules in the UAPI?
How would that work/look like?
defrag (and conntrack) need special handling because loading these modules has no effect on the datapath.
Traditionally, yes, loading was enough, but now with netns being ubiquitous we don't want these to get enabled unless needed.
Ignoring bpf, this happens when user adds nftables/iptables rules that check for conntrack state, use some form of NAT or use e.g. tproxy.
For bpf a flag during link attachment seemed like the best way to go.
Right, I wasn't disputing that having a flag to load a module was a good idea. On the contrary, I was thinking we'd need many more of these if/when BPF wants to take advantage of more netfilter code. Say, if a BPF module wants to call into TPROXY, that module would also need go be loaded and kept around, no?
I was thinking something along the lines of just having a field 'netfilter_modules[]' where userspace could put an arbitrary number of module names into, and we'd load all of them and put a ref into the bpf_link. In principle, we could just have that be a string array of module names, but that's probably a bit cumbersome (and, well, building a generic module loader interface into the bpf_like API is not desirable either). But maybe with an explicit ENUM?
At the moment I only see two flags for this, namely "need defrag" and "need conntrack".
For conntrack, we MIGHT be able to not need a flag but maybe verifier could "guess" based on kfuncs used.
If the verifier can just identify the modules from the kfuncs and do the whole thing automatically, that would of course be even better from an ease-of-use PoV. Not sure what that would take, though? I seem to recall having discussions around these lines before that fell down on various points.
But for defrag, I don't think its good to add a dummy do-nothing kfunc just for expressing the dependency on bpf prog side.
Agreed.
-Toke
Toke Høiland-Jørgensen toke@redhat.com wrote:
Florian Westphal fw@strlen.de writes:
For bpf a flag during link attachment seemed like the best way to go.
Right, I wasn't disputing that having a flag to load a module was a good idea. On the contrary, I was thinking we'd need many more of these if/when BPF wants to take advantage of more netfilter code. Say, if a BPF module wants to call into TPROXY, that module would also need go be loaded and kept around, no?
That seems to be a different topic that has nothing to do with either bpf_link or netfilter?
If the program calls into say, TPROXY, then I'd expect that this needs to be handled via kfuncs, no? Or if I misunderstand, what do you mean by "call into TPROXY"?
And if so, thats already handled at bpf_prog load time, not at link creation time, or do I miss something here?
AFAIU, if prog uses such kfuncs, verifier will grab needed module ref and if module isn't loaded the kfuncs won't be found and program load fails.
I was thinking something along the lines of just having a field 'netfilter_modules[]' where userspace could put an arbitrary number of module names into, and we'd load all of them and put a ref into the bpf_link.
Why? I fail to understand the connection between bpf_link, netfilter and modules. What makes netfilter so special that we need such a module array, and what does that have to do with bpf_link interface?
In principle, we could just have that be a string array f module names, but that's probably a bit cumbersome (and, well, building a generic module loader interface into the bpf_like API is not desirable either). But maybe with an explicit ENUM?
What functionality does that provide? I can't think of a single module where this functionality is needed.
Either we're talking about future kfuncs, then, as far as i understand how kfuncs work, this is handled at bpf_prog load time, not when the bpf_link is created.
Or we are talking about implicit dependencies, where program doesn't call function X but needs functionality handled earlier in the pipeline?
The only two instances I know where this is the case for netfilter is defrag + conntrack.
For conntrack, we MIGHT be able to not need a flag but maybe verifier could "guess" based on kfuncs used.
If the verifier can just identify the modules from the kfuncs and do the whole thing automatically, that would of course be even better from an ease-of-use PoV. Not sure what that would take, though? I seem to recall having discussions around these lines before that fell down on various points.
AFAICS the conntrack kfuncs are wired to nf_conntrack already, so I would expect that the module has to be loaded already for the verifier to accept the program.
Those kfuncs are not yet exposed to NETFILTER program types. Once they are, all that would be needed is for the netfilter bpf_link to be able tp detect that the prog is calling into those kfuncs, and then make the needed register/unregister calls to enable the conntrack hooks.
Wheter thats better than using an explicit "please turn on conntrack for me", I don't know. Perhaps future bpf programs could access skb->_nfct directly without kfuncs so I'd say the flag is a better approach from an uapi point of view.
Florian Westphal fw@strlen.de writes:
Toke Høiland-Jørgensen toke@redhat.com wrote:
Florian Westphal fw@strlen.de writes:
For bpf a flag during link attachment seemed like the best way to go.
Right, I wasn't disputing that having a flag to load a module was a good idea. On the contrary, I was thinking we'd need many more of these if/when BPF wants to take advantage of more netfilter code. Say, if a BPF module wants to call into TPROXY, that module would also need go be loaded and kept around, no?
That seems to be a different topic that has nothing to do with either bpf_link or netfilter?
If the program calls into say, TPROXY, then I'd expect that this needs to be handled via kfuncs, no? Or if I misunderstand, what do you mean by "call into TPROXY"?
And if so, thats already handled at bpf_prog load time, not at link creation time, or do I miss something here?
AFAIU, if prog uses such kfuncs, verifier will grab needed module ref and if module isn't loaded the kfuncs won't be found and program load fails.
...
Or we are talking about implicit dependencies, where program doesn't call function X but needs functionality handled earlier in the pipeline?
The only two instances I know where this is the case for netfilter is defrag + conntrack.
Well, I was kinda mixing the two cases above, sorry about that. The "kfuncs locking the module" was not present in my mind when starting to talk about that bit...
As for the original question, that's answered by your point above: If those two modules are the only ones that are likely to need this, then a flag for each is fine by me - that was the key piece I was missing (I'm not a netfilter expert, as you well know).
Thanks for clarifying, and apologies for the muddled thinking! :)
-Toke
Toke Høiland-Jørgensen toke@redhat.com wrote:
Florian Westphal fw@strlen.de writes: As for the original question, that's answered by your point above: If those two modules are the only ones that are likely to need this, then a flag for each is fine by me - that was the key piece I was missing (I'm not a netfilter expert, as you well know).
No problem, I was worried I was missing an important piece of kfunc plumbing :-)
You do raise a good point though. With kfuncs, module is pinned. So, should a "please turn on defrag for this bpf_link" pin the defrag modules too?
For plain netfilter we don't do that, i.e. you can just do "rmmod nf_defrag_ipv4". But I suspect that for the new bpf-link defrag we probably should grab a reference to prevent unwanted functionality breakage of the bpf prog.
On Thu, Jun 29, 2023 at 04:53:15PM +0200, Florian Westphal wrote:
Toke Høiland-Jørgensen toke@redhat.com wrote:
Florian Westphal fw@strlen.de writes: As for the original question, that's answered by your point above: If those two modules are the only ones that are likely to need this, then a flag for each is fine by me - that was the key piece I was missing (I'm not a netfilter expert, as you well know).
No problem, I was worried I was missing an important piece of kfunc plumbing :-)
You do raise a good point though. With kfuncs, module is pinned. So, should a "please turn on defrag for this bpf_link" pin the defrag modules too?
For plain netfilter we don't do that, i.e. you can just do "rmmod nf_defrag_ipv4". But I suspect that for the new bpf-link defrag we probably should grab a reference to prevent unwanted functionality breakage of the bpf prog.
Ack. Will add to v3.
Thanks, Daniel
linux-kselftest-mirror@lists.linaro.org
-
Daniel Xu -
Florian Westphal -
Toke Høiland-Jørgensen