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Diffstat (limited to 'tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c')
-rw-r--r--tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c865
1 files changed, 865 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c b/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
new file mode 100644
index 000000000000..7ea9785738b5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
@@ -0,0 +1,865 @@
+// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
+/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+#include <asm/errno.h>
+
+#include "bpf_compiler.h"
+
+#define TC_ACT_OK 0
+#define TC_ACT_SHOT 2
+
+#define NSEC_PER_SEC 1000000000L
+
+#define ETH_ALEN 6
+#define ETH_P_IP 0x0800
+#define ETH_P_IPV6 0x86DD
+
+#define tcp_flag_word(tp) (((union tcp_word_hdr *)(tp))->words[3])
+
+#define IP_DF 0x4000
+#define IP_MF 0x2000
+#define IP_OFFSET 0x1fff
+
+#define NEXTHDR_TCP 6
+
+#define TCPOPT_NOP 1
+#define TCPOPT_EOL 0
+#define TCPOPT_MSS 2
+#define TCPOPT_WINDOW 3
+#define TCPOPT_SACK_PERM 4
+#define TCPOPT_TIMESTAMP 8
+
+#define TCPOLEN_MSS 4
+#define TCPOLEN_WINDOW 3
+#define TCPOLEN_SACK_PERM 2
+#define TCPOLEN_TIMESTAMP 10
+
+#define TCP_TS_HZ 1000
+#define TS_OPT_WSCALE_MASK 0xf
+#define TS_OPT_SACK (1 << 4)
+#define TS_OPT_ECN (1 << 5)
+#define TSBITS 6
+#define TSMASK (((__u32)1 << TSBITS) - 1)
+#define TCP_MAX_WSCALE 14U
+
+#define IPV4_MAXLEN 60
+#define TCP_MAXLEN 60
+
+#define DEFAULT_MSS4 1460
+#define DEFAULT_MSS6 1440
+#define DEFAULT_WSCALE 7
+#define DEFAULT_TTL 64
+#define MAX_ALLOWED_PORTS 8
+
+#define MAX_PACKET_OFF 0xffff
+
+#define swap(a, b) \
+ do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
+
+#define __get_unaligned_t(type, ptr) ({ \
+ const struct { type x; } __attribute__((__packed__)) *__pptr = (typeof(__pptr))(ptr); \
+ __pptr->x; \
+})
+
+#define get_unaligned(ptr) __get_unaligned_t(typeof(*(ptr)), (ptr))
+
+struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __type(key, __u32);
+ __type(value, __u64);
+ __uint(max_entries, 2);
+} values SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __type(key, __u32);
+ __type(value, __u16);
+ __uint(max_entries, MAX_ALLOWED_PORTS);
+} allowed_ports SEC(".maps");
+
+/* Some symbols defined in net/netfilter/nf_conntrack_bpf.c are unavailable in
+ * vmlinux.h if CONFIG_NF_CONNTRACK=m, so they are redefined locally.
+ */
+
+struct bpf_ct_opts___local {
+ s32 netns_id;
+ s32 error;
+ u8 l4proto;
+ u8 dir;
+ u8 reserved[2];
+} __attribute__((preserve_access_index));
+
+#define BPF_F_CURRENT_NETNS (-1)
+
+extern struct nf_conn *bpf_xdp_ct_lookup(struct xdp_md *xdp_ctx,
+ struct bpf_sock_tuple *bpf_tuple,
+ __u32 len_tuple,
+ struct bpf_ct_opts___local *opts,
+ __u32 len_opts) __ksym;
+
+extern struct nf_conn *bpf_skb_ct_lookup(struct __sk_buff *skb_ctx,
+ struct bpf_sock_tuple *bpf_tuple,
+ u32 len_tuple,
+ struct bpf_ct_opts___local *opts,
+ u32 len_opts) __ksym;
+
+extern void bpf_ct_release(struct nf_conn *ct) __ksym;
+
+static __always_inline void swap_eth_addr(__u8 *a, __u8 *b)
+{
+ __u8 tmp[ETH_ALEN];
+
+ __builtin_memcpy(tmp, a, ETH_ALEN);
+ __builtin_memcpy(a, b, ETH_ALEN);
+ __builtin_memcpy(b, tmp, ETH_ALEN);
+}
+
+static __always_inline __u16 csum_fold(__u32 csum)
+{
+ csum = (csum & 0xffff) + (csum >> 16);
+ csum = (csum & 0xffff) + (csum >> 16);
+ return (__u16)~csum;
+}
+
+static __always_inline __u16 csum_tcpudp_magic(__be32 saddr, __be32 daddr,
+ __u32 len, __u8 proto,
+ __u32 csum)
+{
+ __u64 s = csum;
+
+ s += (__u32)saddr;
+ s += (__u32)daddr;
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+ s += proto + len;
+#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+ s += (proto + len) << 8;
+#else
+#error Unknown endian
+#endif
+ s = (s & 0xffffffff) + (s >> 32);
+ s = (s & 0xffffffff) + (s >> 32);
+
+ return csum_fold((__u32)s);
+}
+
+static __always_inline __u16 csum_ipv6_magic(const struct in6_addr *saddr,
+ const struct in6_addr *daddr,
+ __u32 len, __u8 proto, __u32 csum)
+{
+ __u64 sum = csum;
+ int i;
+
+ __pragma_loop_unroll
+ for (i = 0; i < 4; i++)
+ sum += (__u32)saddr->in6_u.u6_addr32[i];
+
+ __pragma_loop_unroll
+ for (i = 0; i < 4; i++)
+ sum += (__u32)daddr->in6_u.u6_addr32[i];
+
+ /* Don't combine additions to avoid 32-bit overflow. */
+ sum += bpf_htonl(len);
+ sum += bpf_htonl(proto);
+
+ sum = (sum & 0xffffffff) + (sum >> 32);
+ sum = (sum & 0xffffffff) + (sum >> 32);
+
+ return csum_fold((__u32)sum);
+}
+
+static __always_inline __u64 tcp_clock_ns(void)
+{
+ return bpf_ktime_get_ns();
+}
+
+static __always_inline __u32 tcp_ns_to_ts(__u64 ns)
+{
+ return ns / (NSEC_PER_SEC / TCP_TS_HZ);
+}
+
+static __always_inline __u32 tcp_clock_ms(void)
+{
+ return tcp_ns_to_ts(tcp_clock_ns());
+}
+
+struct tcpopt_context {
+ void *data;
+ void *data_end;
+ __be32 *tsecr;
+ __u8 wscale;
+ bool option_timestamp;
+ bool option_sack;
+ __u32 off;
+};
+
+static __always_inline u8 *next(struct tcpopt_context *ctx, __u32 sz)
+{
+ __u64 off = ctx->off;
+ __u8 *data;
+
+ /* Verifier forbids access to packet when offset exceeds MAX_PACKET_OFF */
+ if (off > MAX_PACKET_OFF - sz)
+ return NULL;
+
+ data = ctx->data + off;
+ barrier_var(data);
+ if (data + sz >= ctx->data_end)
+ return NULL;
+
+ ctx->off += sz;
+ return data;
+}
+
+static int tscookie_tcpopt_parse(struct tcpopt_context *ctx)
+{
+ __u8 *opcode, *opsize, *wscale, *tsecr;
+ __u32 off = ctx->off;
+
+ opcode = next(ctx, 1);
+ if (!opcode)
+ return 1;
+
+ if (*opcode == TCPOPT_EOL)
+ return 1;
+ if (*opcode == TCPOPT_NOP)
+ return 0;
+
+ opsize = next(ctx, 1);
+ if (!opsize || *opsize < 2)
+ return 1;
+
+ switch (*opcode) {
+ case TCPOPT_WINDOW:
+ wscale = next(ctx, 1);
+ if (!wscale)
+ return 1;
+ if (*opsize == TCPOLEN_WINDOW)
+ ctx->wscale = *wscale < TCP_MAX_WSCALE ? *wscale : TCP_MAX_WSCALE;
+ break;
+ case TCPOPT_TIMESTAMP:
+ tsecr = next(ctx, 4);
+ if (!tsecr)
+ return 1;
+ if (*opsize == TCPOLEN_TIMESTAMP) {
+ ctx->option_timestamp = true;
+ /* Client's tsval becomes our tsecr. */
+ *ctx->tsecr = get_unaligned((__be32 *)tsecr);
+ }
+ break;
+ case TCPOPT_SACK_PERM:
+ if (*opsize == TCPOLEN_SACK_PERM)
+ ctx->option_sack = true;
+ break;
+ }
+
+ ctx->off = off + *opsize;
+
+ return 0;
+}
+
+static int tscookie_tcpopt_parse_batch(__u32 index, void *context)
+{
+ int i;
+
+ for (i = 0; i < 7; i++)
+ if (tscookie_tcpopt_parse(context))
+ return 1;
+ return 0;
+}
+
+static __always_inline bool tscookie_init(struct tcphdr *tcp_header,
+ __u16 tcp_len, __be32 *tsval,
+ __be32 *tsecr, void *data, void *data_end)
+{
+ struct tcpopt_context loop_ctx = {
+ .data = data,
+ .data_end = data_end,
+ .tsecr = tsecr,
+ .wscale = TS_OPT_WSCALE_MASK,
+ .option_timestamp = false,
+ .option_sack = false,
+ /* Note: currently verifier would track .off as unbound scalar.
+ * In case if verifier would at some point get smarter and
+ * compute bounded value for this var, beware that it might
+ * hinder bpf_loop() convergence validation.
+ */
+ .off = (__u8 *)(tcp_header + 1) - (__u8 *)data,
+ };
+ u32 cookie;
+
+ bpf_loop(6, tscookie_tcpopt_parse_batch, &loop_ctx, 0);
+
+ if (!loop_ctx.option_timestamp)
+ return false;
+
+ cookie = tcp_clock_ms() & ~TSMASK;
+ cookie |= loop_ctx.wscale & TS_OPT_WSCALE_MASK;
+ if (loop_ctx.option_sack)
+ cookie |= TS_OPT_SACK;
+ if (tcp_header->ece && tcp_header->cwr)
+ cookie |= TS_OPT_ECN;
+ *tsval = bpf_htonl(cookie);
+
+ return true;
+}
+
+static __always_inline void values_get_tcpipopts(__u16 *mss, __u8 *wscale,
+ __u8 *ttl, bool ipv6)
+{
+ __u32 key = 0;
+ __u64 *value;
+
+ value = bpf_map_lookup_elem(&values, &key);
+ if (value && *value != 0) {
+ if (ipv6)
+ *mss = (*value >> 32) & 0xffff;
+ else
+ *mss = *value & 0xffff;
+ *wscale = (*value >> 16) & 0xf;
+ *ttl = (*value >> 24) & 0xff;
+ return;
+ }
+
+ *mss = ipv6 ? DEFAULT_MSS6 : DEFAULT_MSS4;
+ *wscale = DEFAULT_WSCALE;
+ *ttl = DEFAULT_TTL;
+}
+
+static __always_inline void values_inc_synacks(void)
+{
+ __u32 key = 1;
+ __u64 *value;
+
+ value = bpf_map_lookup_elem(&values, &key);
+ if (value)
+ __sync_fetch_and_add(value, 1);
+}
+
+static __always_inline bool check_port_allowed(__u16 port)
+{
+ __u32 i;
+
+ for (i = 0; i < MAX_ALLOWED_PORTS; i++) {
+ __u32 key = i;
+ __u16 *value;
+
+ value = bpf_map_lookup_elem(&allowed_ports, &key);
+
+ if (!value)
+ break;
+ /* 0 is a terminator value. Check it first to avoid matching on
+ * a forbidden port == 0 and returning true.
+ */
+ if (*value == 0)
+ break;
+
+ if (*value == port)
+ return true;
+ }
+
+ return false;
+}
+
+struct header_pointers {
+ struct ethhdr *eth;
+ struct iphdr *ipv4;
+ struct ipv6hdr *ipv6;
+ struct tcphdr *tcp;
+ __u16 tcp_len;
+};
+
+static __always_inline int tcp_dissect(void *data, void *data_end,
+ struct header_pointers *hdr)
+{
+ hdr->eth = data;
+ if (hdr->eth + 1 > data_end)
+ return XDP_DROP;
+
+ switch (bpf_ntohs(hdr->eth->h_proto)) {
+ case ETH_P_IP:
+ hdr->ipv6 = NULL;
+
+ hdr->ipv4 = (void *)hdr->eth + sizeof(*hdr->eth);
+ if (hdr->ipv4 + 1 > data_end)
+ return XDP_DROP;
+ if (hdr->ipv4->ihl * 4 < sizeof(*hdr->ipv4))
+ return XDP_DROP;
+ if (hdr->ipv4->version != 4)
+ return XDP_DROP;
+
+ if (hdr->ipv4->protocol != IPPROTO_TCP)
+ return XDP_PASS;
+
+ hdr->tcp = (void *)hdr->ipv4 + hdr->ipv4->ihl * 4;
+ break;
+ case ETH_P_IPV6:
+ hdr->ipv4 = NULL;
+
+ hdr->ipv6 = (void *)hdr->eth + sizeof(*hdr->eth);
+ if (hdr->ipv6 + 1 > data_end)
+ return XDP_DROP;
+ if (hdr->ipv6->version != 6)
+ return XDP_DROP;
+
+ /* XXX: Extension headers are not supported and could circumvent
+ * XDP SYN flood protection.
+ */
+ if (hdr->ipv6->nexthdr != NEXTHDR_TCP)
+ return XDP_PASS;
+
+ hdr->tcp = (void *)hdr->ipv6 + sizeof(*hdr->ipv6);
+ break;
+ default:
+ /* XXX: VLANs will circumvent XDP SYN flood protection. */
+ return XDP_PASS;
+ }
+
+ if (hdr->tcp + 1 > data_end)
+ return XDP_DROP;
+ hdr->tcp_len = hdr->tcp->doff * 4;
+ if (hdr->tcp_len < sizeof(*hdr->tcp))
+ return XDP_DROP;
+
+ return XDP_TX;
+}
+
+static __always_inline int tcp_lookup(void *ctx, struct header_pointers *hdr, bool xdp)
+{
+ struct bpf_ct_opts___local ct_lookup_opts = {
+ .netns_id = BPF_F_CURRENT_NETNS,
+ .l4proto = IPPROTO_TCP,
+ };
+ struct bpf_sock_tuple tup = {};
+ struct nf_conn *ct;
+ __u32 tup_size;
+
+ if (hdr->ipv4) {
+ /* TCP doesn't normally use fragments, and XDP can't reassemble
+ * them.
+ */
+ if ((hdr->ipv4->frag_off & bpf_htons(IP_DF | IP_MF | IP_OFFSET)) != bpf_htons(IP_DF))
+ return XDP_DROP;
+
+ tup.ipv4.saddr = hdr->ipv4->saddr;
+ tup.ipv4.daddr = hdr->ipv4->daddr;
+ tup.ipv4.sport = hdr->tcp->source;
+ tup.ipv4.dport = hdr->tcp->dest;
+ tup_size = sizeof(tup.ipv4);
+ } else if (hdr->ipv6) {
+ __builtin_memcpy(tup.ipv6.saddr, &hdr->ipv6->saddr, sizeof(tup.ipv6.saddr));
+ __builtin_memcpy(tup.ipv6.daddr, &hdr->ipv6->daddr, sizeof(tup.ipv6.daddr));
+ tup.ipv6.sport = hdr->tcp->source;
+ tup.ipv6.dport = hdr->tcp->dest;
+ tup_size = sizeof(tup.ipv6);
+ } else {
+ /* The verifier can't track that either ipv4 or ipv6 is not
+ * NULL.
+ */
+ return XDP_ABORTED;
+ }
+ if (xdp)
+ ct = bpf_xdp_ct_lookup(ctx, &tup, tup_size, &ct_lookup_opts, sizeof(ct_lookup_opts));
+ else
+ ct = bpf_skb_ct_lookup(ctx, &tup, tup_size, &ct_lookup_opts, sizeof(ct_lookup_opts));
+ if (ct) {
+ unsigned long status = ct->status;
+
+ bpf_ct_release(ct);
+ if (status & IPS_CONFIRMED)
+ return XDP_PASS;
+ } else if (ct_lookup_opts.error != -ENOENT) {
+ return XDP_ABORTED;
+ }
+
+ /* error == -ENOENT || !(status & IPS_CONFIRMED) */
+ return XDP_TX;
+}
+
+static __always_inline __u8 tcp_mkoptions(__be32 *buf, __be32 *tsopt, __u16 mss,
+ __u8 wscale)
+{
+ __be32 *start = buf;
+
+ *buf++ = bpf_htonl((TCPOPT_MSS << 24) | (TCPOLEN_MSS << 16) | mss);
+
+ if (!tsopt)
+ return buf - start;
+
+ if (tsopt[0] & bpf_htonl(1 << 4))
+ *buf++ = bpf_htonl((TCPOPT_SACK_PERM << 24) |
+ (TCPOLEN_SACK_PERM << 16) |
+ (TCPOPT_TIMESTAMP << 8) |
+ TCPOLEN_TIMESTAMP);
+ else
+ *buf++ = bpf_htonl((TCPOPT_NOP << 24) |
+ (TCPOPT_NOP << 16) |
+ (TCPOPT_TIMESTAMP << 8) |
+ TCPOLEN_TIMESTAMP);
+ *buf++ = tsopt[0];
+ *buf++ = tsopt[1];
+
+ if ((tsopt[0] & bpf_htonl(0xf)) != bpf_htonl(0xf))
+ *buf++ = bpf_htonl((TCPOPT_NOP << 24) |
+ (TCPOPT_WINDOW << 16) |
+ (TCPOLEN_WINDOW << 8) |
+ wscale);
+
+ return buf - start;
+}
+
+static __always_inline void tcp_gen_synack(struct tcphdr *tcp_header,
+ __u32 cookie, __be32 *tsopt,
+ __u16 mss, __u8 wscale)
+{
+ void *tcp_options;
+
+ tcp_flag_word(tcp_header) = TCP_FLAG_SYN | TCP_FLAG_ACK;
+ if (tsopt && (tsopt[0] & bpf_htonl(1 << 5)))
+ tcp_flag_word(tcp_header) |= TCP_FLAG_ECE;
+ tcp_header->doff = 5; /* doff is part of tcp_flag_word. */
+ swap(tcp_header->source, tcp_header->dest);
+ tcp_header->ack_seq = bpf_htonl(bpf_ntohl(tcp_header->seq) + 1);
+ tcp_header->seq = bpf_htonl(cookie);
+ tcp_header->window = 0;
+ tcp_header->urg_ptr = 0;
+ tcp_header->check = 0; /* Calculate checksum later. */
+
+ tcp_options = (void *)(tcp_header + 1);
+ tcp_header->doff += tcp_mkoptions(tcp_options, tsopt, mss, wscale);
+}
+
+static __always_inline void tcpv4_gen_synack(struct header_pointers *hdr,
+ __u32 cookie, __be32 *tsopt)
+{
+ __u8 wscale;
+ __u16 mss;
+ __u8 ttl;
+
+ values_get_tcpipopts(&mss, &wscale, &ttl, false);
+
+ swap_eth_addr(hdr->eth->h_source, hdr->eth->h_dest);
+
+ swap(hdr->ipv4->saddr, hdr->ipv4->daddr);
+ hdr->ipv4->check = 0; /* Calculate checksum later. */
+ hdr->ipv4->tos = 0;
+ hdr->ipv4->id = 0;
+ hdr->ipv4->ttl = ttl;
+
+ tcp_gen_synack(hdr->tcp, cookie, tsopt, mss, wscale);
+
+ hdr->tcp_len = hdr->tcp->doff * 4;
+ hdr->ipv4->tot_len = bpf_htons(sizeof(*hdr->ipv4) + hdr->tcp_len);
+}
+
+static __always_inline void tcpv6_gen_synack(struct header_pointers *hdr,
+ __u32 cookie, __be32 *tsopt)
+{
+ __u8 wscale;
+ __u16 mss;
+ __u8 ttl;
+
+ values_get_tcpipopts(&mss, &wscale, &ttl, true);
+
+ swap_eth_addr(hdr->eth->h_source, hdr->eth->h_dest);
+
+ swap(hdr->ipv6->saddr, hdr->ipv6->daddr);
+ *(__be32 *)hdr->ipv6 = bpf_htonl(0x60000000);
+ hdr->ipv6->hop_limit = ttl;
+
+ tcp_gen_synack(hdr->tcp, cookie, tsopt, mss, wscale);
+
+ hdr->tcp_len = hdr->tcp->doff * 4;
+ hdr->ipv6->payload_len = bpf_htons(hdr->tcp_len);
+}
+
+static __always_inline int syncookie_handle_syn(struct header_pointers *hdr,
+ void *ctx,
+ void *data, void *data_end,
+ bool xdp)
+{
+ __u32 old_pkt_size, new_pkt_size;
+ /* Unlike clang 10, clang 11 and 12 generate code that doesn't pass the
+ * BPF verifier if tsopt is not volatile. Volatile forces it to store
+ * the pointer value and use it directly, otherwise tcp_mkoptions is
+ * (mis)compiled like this:
+ * if (!tsopt)
+ * return buf - start;
+ * reg = stored_return_value_of_tscookie_init;
+ * if (reg)
+ * tsopt = tsopt_buf;
+ * else
+ * tsopt = NULL;
+ * ...
+ * *buf++ = tsopt[1];
+ * It creates a dead branch where tsopt is assigned NULL, but the
+ * verifier can't prove it's dead and blocks the program.
+ */
+ __be32 * volatile tsopt = NULL;
+ __be32 tsopt_buf[2] = {};
+ __u16 ip_len;
+ __u32 cookie;
+ __s64 value;
+
+ /* Checksum is not yet verified, but both checksum failure and TCP
+ * header checks return XDP_DROP, so the order doesn't matter.
+ */
+ if (hdr->tcp->fin || hdr->tcp->rst)
+ return XDP_DROP;
+
+ /* Issue SYN cookies on allowed ports, drop SYN packets on blocked
+ * ports.
+ */
+ if (!check_port_allowed(bpf_ntohs(hdr->tcp->dest)))
+ return XDP_DROP;
+
+ if (hdr->ipv4) {
+ /* Check the IPv4 and TCP checksums before creating a SYNACK. */
+ value = bpf_csum_diff(0, 0, (void *)hdr->ipv4, hdr->ipv4->ihl * 4, 0);
+ if (value < 0)
+ return XDP_ABORTED;
+ if (csum_fold(value) != 0)
+ return XDP_DROP; /* Bad IPv4 checksum. */
+
+ value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
+ if (value < 0)
+ return XDP_ABORTED;
+ if (csum_tcpudp_magic(hdr->ipv4->saddr, hdr->ipv4->daddr,
+ hdr->tcp_len, IPPROTO_TCP, value) != 0)
+ return XDP_DROP; /* Bad TCP checksum. */
+
+ ip_len = sizeof(*hdr->ipv4);
+
+ value = bpf_tcp_raw_gen_syncookie_ipv4(hdr->ipv4, hdr->tcp,
+ hdr->tcp_len);
+ } else if (hdr->ipv6) {
+ /* Check the TCP checksum before creating a SYNACK. */
+ value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
+ if (value < 0)
+ return XDP_ABORTED;
+ if (csum_ipv6_magic(&hdr->ipv6->saddr, &hdr->ipv6->daddr,
+ hdr->tcp_len, IPPROTO_TCP, value) != 0)
+ return XDP_DROP; /* Bad TCP checksum. */
+
+ ip_len = sizeof(*hdr->ipv6);
+
+ value = bpf_tcp_raw_gen_syncookie_ipv6(hdr->ipv6, hdr->tcp,
+ hdr->tcp_len);
+ } else {
+ return XDP_ABORTED;
+ }
+
+ if (value < 0)
+ return XDP_ABORTED;
+ cookie = (__u32)value;
+
+ if (tscookie_init((void *)hdr->tcp, hdr->tcp_len,
+ &tsopt_buf[0], &tsopt_buf[1], data, data_end))
+ tsopt = tsopt_buf;
+
+ /* Check that there is enough space for a SYNACK. It also covers
+ * the check that the destination of the __builtin_memmove below
+ * doesn't overflow.
+ */
+ if (data + sizeof(*hdr->eth) + ip_len + TCP_MAXLEN > data_end)
+ return XDP_ABORTED;
+
+ if (hdr->ipv4) {
+ if (hdr->ipv4->ihl * 4 > sizeof(*hdr->ipv4)) {
+ struct tcphdr *new_tcp_header;
+
+ new_tcp_header = data + sizeof(*hdr->eth) + sizeof(*hdr->ipv4);
+ __builtin_memmove(new_tcp_header, hdr->tcp, sizeof(*hdr->tcp));
+ hdr->tcp = new_tcp_header;
+
+ hdr->ipv4->ihl = sizeof(*hdr->ipv4) / 4;
+ }
+
+ tcpv4_gen_synack(hdr, cookie, tsopt);
+ } else if (hdr->ipv6) {
+ tcpv6_gen_synack(hdr, cookie, tsopt);
+ } else {
+ return XDP_ABORTED;
+ }
+
+ /* Recalculate checksums. */
+ hdr->tcp->check = 0;
+ value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
+ if (value < 0)
+ return XDP_ABORTED;
+ if (hdr->ipv4) {
+ hdr->tcp->check = csum_tcpudp_magic(hdr->ipv4->saddr,
+ hdr->ipv4->daddr,
+ hdr->tcp_len,
+ IPPROTO_TCP,
+ value);
+
+ hdr->ipv4->check = 0;
+ value = bpf_csum_diff(0, 0, (void *)hdr->ipv4, sizeof(*hdr->ipv4), 0);
+ if (value < 0)
+ return XDP_ABORTED;
+ hdr->ipv4->check = csum_fold(value);
+ } else if (hdr->ipv6) {
+ hdr->tcp->check = csum_ipv6_magic(&hdr->ipv6->saddr,
+ &hdr->ipv6->daddr,
+ hdr->tcp_len,
+ IPPROTO_TCP,
+ value);
+ } else {
+ return XDP_ABORTED;
+ }
+
+ /* Set the new packet size. */
+ old_pkt_size = data_end - data;
+ new_pkt_size = sizeof(*hdr->eth) + ip_len + hdr->tcp->doff * 4;
+ if (xdp) {
+ if (bpf_xdp_adjust_tail(ctx, new_pkt_size - old_pkt_size))
+ return XDP_ABORTED;
+ } else {
+ if (bpf_skb_change_tail(ctx, new_pkt_size, 0))
+ return XDP_ABORTED;
+ }
+
+ values_inc_synacks();
+
+ return XDP_TX;
+}
+
+static __always_inline int syncookie_handle_ack(struct header_pointers *hdr)
+{
+ int err;
+
+ if (hdr->tcp->rst)
+ return XDP_DROP;
+
+ if (hdr->ipv4)
+ err = bpf_tcp_raw_check_syncookie_ipv4(hdr->ipv4, hdr->tcp);
+ else if (hdr->ipv6)
+ err = bpf_tcp_raw_check_syncookie_ipv6(hdr->ipv6, hdr->tcp);
+ else
+ return XDP_ABORTED;
+ if (err)
+ return XDP_DROP;
+
+ return XDP_PASS;
+}
+
+static __always_inline int syncookie_part1(void *ctx, void *data, void *data_end,
+ struct header_pointers *hdr, bool xdp)
+{
+ int ret;
+
+ ret = tcp_dissect(data, data_end, hdr);
+ if (ret != XDP_TX)
+ return ret;
+
+ ret = tcp_lookup(ctx, hdr, xdp);
+ if (ret != XDP_TX)
+ return ret;
+
+ /* Packet is TCP and doesn't belong to an established connection. */
+
+ if ((hdr->tcp->syn ^ hdr->tcp->ack) != 1)
+ return XDP_DROP;
+
+ /* Grow the TCP header to TCP_MAXLEN to be able to pass any hdr->tcp_len
+ * to bpf_tcp_raw_gen_syncookie_ipv{4,6} and pass the verifier.
+ */
+ if (xdp) {
+ if (bpf_xdp_adjust_tail(ctx, TCP_MAXLEN - hdr->tcp_len))
+ return XDP_ABORTED;
+ } else {
+ /* Without volatile the verifier throws this error:
+ * R9 32-bit pointer arithmetic prohibited
+ */
+ volatile u64 old_len = data_end - data;
+
+ if (bpf_skb_change_tail(ctx, old_len + TCP_MAXLEN - hdr->tcp_len, 0))
+ return XDP_ABORTED;
+ }
+
+ return XDP_TX;
+}
+
+static __always_inline int syncookie_part2(void *ctx, void *data, void *data_end,
+ struct header_pointers *hdr, bool xdp)
+{
+ if (hdr->ipv4) {
+ hdr->eth = data;
+ hdr->ipv4 = (void *)hdr->eth + sizeof(*hdr->eth);
+ /* IPV4_MAXLEN is needed when calculating checksum.
+ * At least sizeof(struct iphdr) is needed here to access ihl.
+ */
+ if ((void *)hdr->ipv4 + IPV4_MAXLEN > data_end)
+ return XDP_ABORTED;
+ hdr->tcp = (void *)hdr->ipv4 + hdr->ipv4->ihl * 4;
+ } else if (hdr->ipv6) {
+ hdr->eth = data;
+ hdr->ipv6 = (void *)hdr->eth + sizeof(*hdr->eth);
+ hdr->tcp = (void *)hdr->ipv6 + sizeof(*hdr->ipv6);
+ } else {
+ return XDP_ABORTED;
+ }
+
+ if ((void *)hdr->tcp + TCP_MAXLEN > data_end)
+ return XDP_ABORTED;
+
+ /* We run out of registers, tcp_len gets spilled to the stack, and the
+ * verifier forgets its min and max values checked above in tcp_dissect.
+ */
+ hdr->tcp_len = hdr->tcp->doff * 4;
+ if (hdr->tcp_len < sizeof(*hdr->tcp))
+ return XDP_ABORTED;
+
+ return hdr->tcp->syn ? syncookie_handle_syn(hdr, ctx, data, data_end, xdp) :
+ syncookie_handle_ack(hdr);
+}
+
+SEC("xdp")
+int syncookie_xdp(struct xdp_md *ctx)
+{
+ void *data_end = (void *)(long)ctx->data_end;
+ void *data = (void *)(long)ctx->data;
+ struct header_pointers hdr;
+ int ret;
+
+ ret = syncookie_part1(ctx, data, data_end, &hdr, true);
+ if (ret != XDP_TX)
+ return ret;
+
+ data_end = (void *)(long)ctx->data_end;
+ data = (void *)(long)ctx->data;
+
+ return syncookie_part2(ctx, data, data_end, &hdr, true);
+}
+
+SEC("tc")
+int syncookie_tc(struct __sk_buff *skb)
+{
+ void *data_end = (void *)(long)skb->data_end;
+ void *data = (void *)(long)skb->data;
+ struct header_pointers hdr;
+ int ret;
+
+ ret = syncookie_part1(skb, data, data_end, &hdr, false);
+ if (ret != XDP_TX)
+ return ret == XDP_PASS ? TC_ACT_OK : TC_ACT_SHOT;
+
+ data_end = (void *)(long)skb->data_end;
+ data = (void *)(long)skb->data;
+
+ ret = syncookie_part2(skb, data, data_end, &hdr, false);
+ switch (ret) {
+ case XDP_PASS:
+ return TC_ACT_OK;
+ case XDP_TX:
+ return bpf_redirect(skb->ifindex, 0);
+ default:
+ return TC_ACT_SHOT;
+ }
+}
+
+char _license[] SEC("license") = "GPL";
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.