Merge tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next

Daniel Borkmann says:

====================
pull-request: bpf-next 2024-01-26

We've added 107 non-merge commits during the last 4 day(s) which contain
a total of 101 files changed, 6009 insertions(+), 1260 deletions(-).

The main changes are:

1) Add BPF token support to delegate a subset of BPF subsystem
   functionality from privileged system-wide daemons such as systemd
   through special mount options for userns-bound BPF fs to a trusted
   & unprivileged application. With addressed changes from Christian
   and Linus' reviews, from Andrii Nakryiko.

2) Support registration of struct_ops types from modules which helps
   projects like fuse-bpf that seeks to implement a new struct_ops type,
   from Kui-Feng Lee.

3) Add support for retrieval of cookies for perf/kprobe multi links,
   from Jiri Olsa.

4) Bigger batch of prep-work for the BPF verifier to eventually support
   preserving boundaries and tracking scalars on narrowing fills,
   from Maxim Mikityanskiy.

5) Extend the tc BPF flavor to support arbitrary TCP SYN cookies to help
   with the scenario of SYN floods, from Kuniyuki Iwashima.

6) Add code generation to inline the bpf_kptr_xchg() helper which
   improves performance when stashing/popping the allocated BPF objects,
   from Hou Tao.

7) Extend BPF verifier to track aligned ST stores as imprecise spilled
   registers, from Yonghong Song.

8) Several fixes to BPF selftests around inline asm constraints and
   unsupported VLA code generation, from Jose E. Marchesi.

9) Various updates to the BPF IETF instruction set draft document such
   as the introduction of conformance groups for instructions,
   from Dave Thaler.

10) Fix BPF verifier to make infinite loop detection in is_state_visited()
    exact to catch some too lax spill/fill corner cases,
    from Eduard Zingerman.

11) Refactor the BPF verifier pointer ALU check to allow ALU explicitly
    instead of implicitly for various register types, from Hao Sun.

12) Fix the flaky tc_redirect_dtime BPF selftest due to slowness
    in neighbor advertisement at setup time, from Martin KaFai Lau.

13) Change BPF selftests to skip callback tests for the case when the
    JIT is disabled, from Tiezhu Yang.

14) Add a small extension to libbpf which allows to auto create
    a map-in-map's inner map, from Andrey Grafin.

* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (107 commits)
  selftests/bpf: Add missing line break in test_verifier
  bpf, docs: Clarify definitions of various instructions
  bpf: Fix error checks against bpf_get_btf_vmlinux().
  bpf: One more maintainer for libbpf and BPF selftests
  selftests/bpf: Incorporate LSM policy to token-based tests
  selftests/bpf: Add tests for LIBBPF_BPF_TOKEN_PATH envvar
  libbpf: Support BPF token path setting through LIBBPF_BPF_TOKEN_PATH envvar
  selftests/bpf: Add tests for BPF object load with implicit token
  selftests/bpf: Add BPF object loading tests with explicit token passing
  libbpf: Wire up BPF token support at BPF object level
  libbpf: Wire up token_fd into feature probing logic
  libbpf: Move feature detection code into its own file
  libbpf: Further decouple feature checking logic from bpf_object
  libbpf: Split feature detectors definitions from cached results
  selftests/bpf: Utilize string values for delegate_xxx mount options
  bpf: Support symbolic BPF FS delegation mount options
  bpf: Fail BPF_TOKEN_CREATE if no delegation option was set on BPF FS
  bpf,selinux: Allocate bpf_security_struct per BPF token
  selftests/bpf: Add BPF token-enabled tests
  libbpf: Add BPF token support to bpf_prog_load() API
  ...
====================

Link: https://lore.kernel.org/r/20240126215710.19855-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 572 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
new file mode 100644
index 000000000000..a5501b29979a
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
@@ -0,0 +1,572 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright Amazon.com Inc. or its affiliates. */
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+#include "bpf_tracing_net.h"
+#include "bpf_kfuncs.h"
+#include "test_siphash.h"
+#include "test_tcp_custom_syncookie.h"
+
+/* Hash is calculated for each client and split into ISN and TS.
+ *
+ *       MSB                                   LSB
+ * ISN:  | 31 ... 8 | 7 6 |   5 |    4 | 3 2 1 0 |
+ *       |   Hash_1 | MSS | ECN | SACK |  WScale |
+ *
+ * TS:   | 31 ... 8 |          7 ... 0           |
+ *       |   Random |           Hash_2           |
+ */
+#define COOKIE_BITS	8
+#define COOKIE_MASK	(((__u32)1 << COOKIE_BITS) - 1)
+
+enum {
+	/* 0xf is invalid thus means that SYN did not have WScale. */
+	BPF_SYNCOOKIE_WSCALE_MASK	= (1 << 4) - 1,
+	BPF_SYNCOOKIE_SACK		= (1 << 4),
+	BPF_SYNCOOKIE_ECN		= (1 << 5),
+};
+
+#define MSS_LOCAL_IPV4	65495
+#define MSS_LOCAL_IPV6	65476
+
+const __u16 msstab4[] = {
+	536,
+	1300,
+	1460,
+	MSS_LOCAL_IPV4,
+};
+
+const __u16 msstab6[] = {
+	1280 - 60, /* IPV6_MIN_MTU - 60 */
+	1480 - 60,
+	9000 - 60,
+	MSS_LOCAL_IPV6,
+};
+
+static siphash_key_t test_key_siphash = {
+	{ 0x0706050403020100ULL, 0x0f0e0d0c0b0a0908ULL }
+};
+
+struct tcp_syncookie {
+	struct __sk_buff *skb;
+	void *data_end;
+	struct ethhdr *eth;
+	struct iphdr *ipv4;
+	struct ipv6hdr *ipv6;
+	struct tcphdr *tcp;
+	union {
+		char *ptr;
+		__be32 *ptr32;
+	};
+	struct bpf_tcp_req_attrs attrs;
+	u32 cookie;
+	u64 first;
+};
+
+bool handled_syn, handled_ack;
+
+static int tcp_load_headers(struct tcp_syncookie *ctx)
+{
+	ctx->data_end = (void *)(long)ctx->skb->data_end;
+	ctx->eth = (struct ethhdr *)(long)ctx->skb->data;
+
+	if (ctx->eth + 1 > ctx->data_end)
+		goto err;
+
+	switch (bpf_ntohs(ctx->eth->h_proto)) {
+	case ETH_P_IP:
+		ctx->ipv4 = (struct iphdr *)(ctx->eth + 1);
+
+		if (ctx->ipv4 + 1 > ctx->data_end)
+			goto err;
+
+		if (ctx->ipv4->ihl != sizeof(*ctx->ipv4) / 4)
+			goto err;
+
+		if (ctx->ipv4->version != 4)
+			goto err;
+
+		if (ctx->ipv4->protocol != IPPROTO_TCP)
+			goto err;
+
+		ctx->tcp = (struct tcphdr *)(ctx->ipv4 + 1);
+		break;
+	case ETH_P_IPV6:
+		ctx->ipv6 = (struct ipv6hdr *)(ctx->eth + 1);
+
+		if (ctx->ipv6 + 1 > ctx->data_end)
+			goto err;
+
+		if (ctx->ipv6->version != 6)
+			goto err;
+
+		if (ctx->ipv6->nexthdr != NEXTHDR_TCP)
+			goto err;
+
+		ctx->tcp = (struct tcphdr *)(ctx->ipv6 + 1);
+		break;
+	default:
+		goto err;
+	}
+
+	if (ctx->tcp + 1 > ctx->data_end)
+		goto err;
+
+	return 0;
+err:
+	return -1;
+}
+
+static int tcp_reload_headers(struct tcp_syncookie *ctx)
+{
+	/* Without volatile,
+	 * R3 32-bit pointer arithmetic prohibited
+	 */
+	volatile u64 data_len = ctx->skb->data_end - ctx->skb->data;
+
+	if (ctx->tcp->doff < sizeof(*ctx->tcp) / 4)
+		goto err;
+
+	/* Needed to calculate csum and parse TCP options. */
+	if (bpf_skb_change_tail(ctx->skb, data_len + 60 - ctx->tcp->doff * 4, 0))
+		goto err;
+
+	ctx->data_end = (void *)(long)ctx->skb->data_end;
+	ctx->eth = (struct ethhdr *)(long)ctx->skb->data;
+	if (ctx->ipv4) {
+		ctx->ipv4 = (struct iphdr *)(ctx->eth + 1);
+		ctx->ipv6 = NULL;
+		ctx->tcp = (struct tcphdr *)(ctx->ipv4 + 1);
+	} else {
+		ctx->ipv4 = NULL;
+		ctx->ipv6 = (struct ipv6hdr *)(ctx->eth + 1);
+		ctx->tcp = (struct tcphdr *)(ctx->ipv6 + 1);
+	}
+
+	if ((void *)ctx->tcp + 60 > ctx->data_end)
+		goto err;
+
+	return 0;
+err:
+	return -1;
+}
+
+static __sum16 tcp_v4_csum(struct tcp_syncookie *ctx, __wsum csum)
+{
+	return csum_tcpudp_magic(ctx->ipv4->saddr, ctx->ipv4->daddr,
+				 ctx->tcp->doff * 4, IPPROTO_TCP, csum);
+}
+
+static __sum16 tcp_v6_csum(struct tcp_syncookie *ctx, __wsum csum)
+{
+	return csum_ipv6_magic(&ctx->ipv6->saddr, &ctx->ipv6->daddr,
+			       ctx->tcp->doff * 4, IPPROTO_TCP, csum);
+}
+
+static int tcp_validate_header(struct tcp_syncookie *ctx)
+{
+	s64 csum;
+
+	if (tcp_reload_headers(ctx))
+		goto err;
+
+	csum = bpf_csum_diff(0, 0, (void *)ctx->tcp, ctx->tcp->doff * 4, 0);
+	if (csum < 0)
+		goto err;
+
+	if (ctx->ipv4) {
+		/* check tcp_v4_csum(csum) is 0 if not on lo. */
+
+		csum = bpf_csum_diff(0, 0, (void *)ctx->ipv4, ctx->ipv4->ihl * 4, 0);
+		if (csum < 0)
+			goto err;
+
+		if (csum_fold(csum) != 0)
+			goto err;
+	} else if (ctx->ipv6) {
+		/* check tcp_v6_csum(csum) is 0 if not on lo. */
+	}
+
+	return 0;
+err:
+	return -1;
+}
+
+static int tcp_parse_option(__u32 index, struct tcp_syncookie *ctx)
+{
+	char opcode, opsize;
+
+	if (ctx->ptr + 1 > ctx->data_end)
+		goto stop;
+
+	opcode = *ctx->ptr++;
+
+	if (opcode == TCPOPT_EOL)
+		goto stop;
+
+	if (opcode == TCPOPT_NOP)
+		goto next;
+
+	if (ctx->ptr + 1 > ctx->data_end)
+		goto stop;
+
+	opsize = *ctx->ptr++;
+
+	if (opsize < 2)
+		goto stop;
+
+	switch (opcode) {
+	case TCPOPT_MSS:
+		if (opsize == TCPOLEN_MSS && ctx->tcp->syn &&
+		    ctx->ptr + (TCPOLEN_MSS - 2) < ctx->data_end)
+			ctx->attrs.mss = get_unaligned_be16(ctx->ptr);
+		break;
+	case TCPOPT_WINDOW:
+		if (opsize == TCPOLEN_WINDOW && ctx->tcp->syn &&
+		    ctx->ptr + (TCPOLEN_WINDOW - 2) < ctx->data_end) {
+			ctx->attrs.wscale_ok = 1;
+			ctx->attrs.snd_wscale = *ctx->ptr;
+		}
+		break;
+	case TCPOPT_TIMESTAMP:
+		if (opsize == TCPOLEN_TIMESTAMP &&
+		    ctx->ptr + (TCPOLEN_TIMESTAMP - 2) < ctx->data_end) {
+			ctx->attrs.rcv_tsval = get_unaligned_be32(ctx->ptr);
+			ctx->attrs.rcv_tsecr = get_unaligned_be32(ctx->ptr + 4);
+
+			if (ctx->tcp->syn && ctx->attrs.rcv_tsecr)
+				ctx->attrs.tstamp_ok = 0;
+			else
+				ctx->attrs.tstamp_ok = 1;
+		}
+		break;
+	case TCPOPT_SACK_PERM:
+		if (opsize == TCPOLEN_SACK_PERM && ctx->tcp->syn &&
+		    ctx->ptr + (TCPOLEN_SACK_PERM - 2) < ctx->data_end)
+			ctx->attrs.sack_ok = 1;
+		break;
+	}
+
+	ctx->ptr += opsize - 2;
+next:
+	return 0;
+stop:
+	return 1;
+}
+
+static void tcp_parse_options(struct tcp_syncookie *ctx)
+{
+	ctx->ptr = (char *)(ctx->tcp + 1);
+
+	bpf_loop(40, tcp_parse_option, ctx, 0);
+}
+
+static int tcp_validate_sysctl(struct tcp_syncookie *ctx)
+{
+	if ((ctx->ipv4 && ctx->attrs.mss != MSS_LOCAL_IPV4) ||
+	    (ctx->ipv6 && ctx->attrs.mss != MSS_LOCAL_IPV6))
+		goto err;
+
+	if (!ctx->attrs.wscale_ok || ctx->attrs.snd_wscale != 7)
+		goto err;
+
+	if (!ctx->attrs.tstamp_ok)
+		goto err;
+
+	if (!ctx->attrs.sack_ok)
+		goto err;
+
+	if (!ctx->tcp->ece || !ctx->tcp->cwr)
+		goto err;
+
+	return 0;
+err:
+	return -1;
+}
+
+static void tcp_prepare_cookie(struct tcp_syncookie *ctx)
+{
+	u32 seq = bpf_ntohl(ctx->tcp->seq);
+	u64 first = 0, second;
+	int mssind = 0;
+	u32 hash;
+
+	if (ctx->ipv4) {
+		for (mssind = ARRAY_SIZE(msstab4) - 1; mssind; mssind--)
+			if (ctx->attrs.mss >= msstab4[mssind])
+				break;
+
+		ctx->attrs.mss = msstab4[mssind];
+
+		first = (u64)ctx->ipv4->saddr << 32 | ctx->ipv4->daddr;
+	} else if (ctx->ipv6) {
+		for (mssind = ARRAY_SIZE(msstab6) - 1; mssind; mssind--)
+			if (ctx->attrs.mss >= msstab6[mssind])
+				break;
+
+		ctx->attrs.mss = msstab6[mssind];
+
+		first = (u64)ctx->ipv6->saddr.in6_u.u6_addr8[0] << 32 |
+			ctx->ipv6->daddr.in6_u.u6_addr32[0];
+	}
+
+	second = (u64)seq << 32 | ctx->tcp->source << 16 | ctx->tcp->dest;
+	hash = siphash_2u64(first, second, &test_key_siphash);
+
+	if (ctx->attrs.tstamp_ok) {
+		ctx->attrs.rcv_tsecr = bpf_get_prandom_u32();
+		ctx->attrs.rcv_tsecr &= ~COOKIE_MASK;
+		ctx->attrs.rcv_tsecr |= hash & COOKIE_MASK;
+	}
+
+	hash &= ~COOKIE_MASK;
+	hash |= mssind << 6;
+
+	if (ctx->attrs.wscale_ok)
+		hash |= ctx->attrs.snd_wscale & BPF_SYNCOOKIE_WSCALE_MASK;
+
+	if (ctx->attrs.sack_ok)
+		hash |= BPF_SYNCOOKIE_SACK;
+
+	if (ctx->attrs.tstamp_ok && ctx->tcp->ece && ctx->tcp->cwr)
+		hash |= BPF_SYNCOOKIE_ECN;
+
+	ctx->cookie = hash;
+}
+
+static void tcp_write_options(struct tcp_syncookie *ctx)
+{
+	ctx->ptr32 = (__be32 *)(ctx->tcp + 1);
+
+	*ctx->ptr32++ = bpf_htonl(TCPOPT_MSS << 24 | TCPOLEN_MSS << 16 |
+				  ctx->attrs.mss);
+
+	if (ctx->attrs.wscale_ok)
+		*ctx->ptr32++ = bpf_htonl(TCPOPT_NOP << 24 |
+					  TCPOPT_WINDOW << 16 |
+					  TCPOLEN_WINDOW << 8 |
+					  ctx->attrs.snd_wscale);
+
+	if (ctx->attrs.tstamp_ok) {
+		if (ctx->attrs.sack_ok)
+			*ctx->ptr32++ = bpf_htonl(TCPOPT_SACK_PERM << 24 |
+						  TCPOLEN_SACK_PERM << 16 |
+						  TCPOPT_TIMESTAMP << 8 |
+						  TCPOLEN_TIMESTAMP);
+		else
+			*ctx->ptr32++ = bpf_htonl(TCPOPT_NOP << 24 |
+						  TCPOPT_NOP << 16 |
+						  TCPOPT_TIMESTAMP << 8 |
+						  TCPOLEN_TIMESTAMP);
+
+		*ctx->ptr32++ = bpf_htonl(ctx->attrs.rcv_tsecr);
+		*ctx->ptr32++ = bpf_htonl(ctx->attrs.rcv_tsval);
+	} else if (ctx->attrs.sack_ok) {
+		*ctx->ptr32++ = bpf_htonl(TCPOPT_NOP << 24 |
+					  TCPOPT_NOP << 16 |
+					  TCPOPT_SACK_PERM << 8 |
+					  TCPOLEN_SACK_PERM);
+	}
+}
+
+static int tcp_handle_syn(struct tcp_syncookie *ctx)
+{
+	s64 csum;
+
+	if (tcp_validate_header(ctx))
+		goto err;
+
+	tcp_parse_options(ctx);
+
+	if (tcp_validate_sysctl(ctx))
+		goto err;
+
+	tcp_prepare_cookie(ctx);
+	tcp_write_options(ctx);
+
+	swap(ctx->tcp->source, ctx->tcp->dest);
+	ctx->tcp->check = 0;
+	ctx->tcp->ack_seq = bpf_htonl(bpf_ntohl(ctx->tcp->seq) + 1);
+	ctx->tcp->seq = bpf_htonl(ctx->cookie);
+	ctx->tcp->doff = ((long)ctx->ptr32 - (long)ctx->tcp) >> 2;
+	ctx->tcp->ack = 1;
+	if (!ctx->attrs.tstamp_ok || !ctx->tcp->ece || !ctx->tcp->cwr)
+		ctx->tcp->ece = 0;
+	ctx->tcp->cwr = 0;
+
+	csum = bpf_csum_diff(0, 0, (void *)ctx->tcp, ctx->tcp->doff * 4, 0);
+	if (csum < 0)
+		goto err;
+
+	if (ctx->ipv4) {
+		swap(ctx->ipv4->saddr, ctx->ipv4->daddr);
+		ctx->tcp->check = tcp_v4_csum(ctx, csum);
+
+		ctx->ipv4->check = 0;
+		ctx->ipv4->tos = 0;
+		ctx->ipv4->tot_len = bpf_htons((long)ctx->ptr32 - (long)ctx->ipv4);
+		ctx->ipv4->id = 0;
+		ctx->ipv4->ttl = 64;
+
+		csum = bpf_csum_diff(0, 0, (void *)ctx->ipv4, sizeof(*ctx->ipv4), 0);
+		if (csum < 0)
+			goto err;
+
+		ctx->ipv4->check = csum_fold(csum);
+	} else if (ctx->ipv6) {
+		swap(ctx->ipv6->saddr, ctx->ipv6->daddr);
+		ctx->tcp->check = tcp_v6_csum(ctx, csum);
+
+		*(__be32 *)ctx->ipv6 = bpf_htonl(0x60000000);
+		ctx->ipv6->payload_len = bpf_htons((long)ctx->ptr32 - (long)ctx->tcp);
+		ctx->ipv6->hop_limit = 64;
+	}
+
+	swap_array(ctx->eth->h_source, ctx->eth->h_dest);
+
+	if (bpf_skb_change_tail(ctx->skb, (long)ctx->ptr32 - (long)ctx->eth, 0))
+		goto err;
+
+	return bpf_redirect(ctx->skb->ifindex, 0);
+err:
+	return TC_ACT_SHOT;
+}
+
+static int tcp_validate_cookie(struct tcp_syncookie *ctx)
+{
+	u32 cookie = bpf_ntohl(ctx->tcp->ack_seq) - 1;
+	u32 seq = bpf_ntohl(ctx->tcp->seq) - 1;
+	u64 first = 0, second;
+	int mssind;
+	u32 hash;
+
+	if (ctx->ipv4)
+		first = (u64)ctx->ipv4->saddr << 32 | ctx->ipv4->daddr;
+	else if (ctx->ipv6)
+		first = (u64)ctx->ipv6->saddr.in6_u.u6_addr8[0] << 32 |
+			ctx->ipv6->daddr.in6_u.u6_addr32[0];
+
+	second = (u64)seq << 32 | ctx->tcp->source << 16 | ctx->tcp->dest;
+	hash = siphash_2u64(first, second, &test_key_siphash);
+
+	if (ctx->attrs.tstamp_ok)
+		hash -= ctx->attrs.rcv_tsecr & COOKIE_MASK;
+	else
+		hash &= ~COOKIE_MASK;
+
+	hash -= cookie & ~COOKIE_MASK;
+	if (hash)
+		goto err;
+
+	mssind = (cookie & (3 << 6)) >> 6;
+	if (ctx->ipv4) {
+		if (mssind > ARRAY_SIZE(msstab4))
+			goto err;
+
+		ctx->attrs.mss = msstab4[mssind];
+	} else {
+		if (mssind > ARRAY_SIZE(msstab6))
+			goto err;
+
+		ctx->attrs.mss = msstab6[mssind];
+	}
+
+	ctx->attrs.snd_wscale = cookie & BPF_SYNCOOKIE_WSCALE_MASK;
+	ctx->attrs.rcv_wscale = ctx->attrs.snd_wscale;
+	ctx->attrs.wscale_ok = ctx->attrs.snd_wscale == BPF_SYNCOOKIE_WSCALE_MASK;
+	ctx->attrs.sack_ok = cookie & BPF_SYNCOOKIE_SACK;
+	ctx->attrs.ecn_ok = cookie & BPF_SYNCOOKIE_ECN;
+
+	return 0;
+err:
+	return -1;
+}
+
+static int tcp_handle_ack(struct tcp_syncookie *ctx)
+{
+	struct bpf_sock_tuple tuple;
+	struct bpf_sock *skc;
+	int ret = TC_ACT_OK;
+	struct sock *sk;
+	u32 tuple_size;
+
+	if (ctx->ipv4) {
+		tuple.ipv4.saddr = ctx->ipv4->saddr;
+		tuple.ipv4.daddr = ctx->ipv4->daddr;
+		tuple.ipv4.sport = ctx->tcp->source;
+		tuple.ipv4.dport = ctx->tcp->dest;
+		tuple_size = sizeof(tuple.ipv4);
+	} else if (ctx->ipv6) {
+		__builtin_memcpy(tuple.ipv6.saddr, &ctx->ipv6->saddr, sizeof(tuple.ipv6.saddr));
+		__builtin_memcpy(tuple.ipv6.daddr, &ctx->ipv6->daddr, sizeof(tuple.ipv6.daddr));
+		tuple.ipv6.sport = ctx->tcp->source;
+		tuple.ipv6.dport = ctx->tcp->dest;
+		tuple_size = sizeof(tuple.ipv6);
+	} else {
+		goto out;
+	}
+
+	skc = bpf_skc_lookup_tcp(ctx->skb, &tuple, tuple_size, -1, 0);
+	if (!skc)
+		goto out;
+
+	if (skc->state != TCP_LISTEN)
+		goto release;
+
+	sk = (struct sock *)bpf_skc_to_tcp_sock(skc);
+	if (!sk)
+		goto err;
+
+	if (tcp_validate_header(ctx))
+		goto err;
+
+	tcp_parse_options(ctx);
+
+	if (tcp_validate_cookie(ctx))
+		goto err;
+
+	ret = bpf_sk_assign_tcp_reqsk(ctx->skb, sk, &ctx->attrs, sizeof(ctx->attrs));
+	if (ret < 0)
+		goto err;
+
+release:
+	bpf_sk_release(skc);
+out:
+	return ret;
+
+err:
+	ret = TC_ACT_SHOT;
+	goto release;
+}
+
+SEC("tc")
+int tcp_custom_syncookie(struct __sk_buff *skb)
+{
+	struct tcp_syncookie ctx = {
+		.skb = skb,
+	};
+
+	if (tcp_load_headers(&ctx))
+		return TC_ACT_OK;
+
+	if (ctx.tcp->rst)
+		return TC_ACT_OK;
+
+	if (ctx.tcp->syn) {
+		if (ctx.tcp->ack)
+			return TC_ACT_OK;
+
+		handled_syn = true;
+
+		return tcp_handle_syn(&ctx);
+	}
+
+	handled_ack = true;
+
+	return tcp_handle_ack(&ctx);
+}
+
+char _license[] SEC("license") = "GPL";