diff --git a/Makefile b/Makefile index 9edb837..88ad10c 100644 --- a/Makefile +++ b/Makefile @@ -25,6 +25,7 @@ SUBDIRS += tc-policy SUBDIRS += traffic-pacing-edt SUBDIRS += AF_XDP-forwarding SUBDIRS += AF_XDP-example +SUBDIRS += xdp-synproxy .PHONY: check_submodule help clobber distclean clean $(SUBDIRS) diff --git a/headers/vmlinux/vmlinux_common.h b/headers/vmlinux/vmlinux_common.h index 7216992..ff0b008 100644 --- a/headers/vmlinux/vmlinux_common.h +++ b/headers/vmlinux/vmlinux_common.h @@ -1,6 +1,13 @@ #ifndef __VMLINUX_COMMON_H__ #define __VMLINUX_COMMON_H__ +enum { + false = 0, + true = 1, +}; + +typedef _Bool bool; + struct list_head { struct list_head *next; struct list_head *prev; diff --git a/headers/vmlinux/vmlinux_net.h b/headers/vmlinux/vmlinux_net.h index 1afcc5d..89f0871 100644 --- a/headers/vmlinux/vmlinux_net.h +++ b/headers/vmlinux/vmlinux_net.h @@ -135,4 +135,13 @@ struct sk_buff { struct skb_ext *extensions; }; +struct nf_conn { + unsigned long status; +}; + +enum ip_conntrack_status { + /* Connection is confirmed: originating packet has left box */ + IPS_CONFIRMED_BIT = 3, +}; + #endif /* __VMLINUX_NET_H__ */ diff --git a/xdp-synproxy/Makefile b/xdp-synproxy/Makefile new file mode 100644 index 0000000..a445521 --- /dev/null +++ b/xdp-synproxy/Makefile @@ -0,0 +1,9 @@ +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) + +USER_TARGETS := xdp_synproxy +BPF_TARGETS := xdp_synproxy_kern +BPF_SKEL_OBJ := xdp_synproxy_kern.o + +LIB_DIR = ../lib + +include $(LIB_DIR)/common.mk diff --git a/xdp-synproxy/README.org b/xdp-synproxy/README.org new file mode 100644 index 0000000..528bed7 --- /dev/null +++ b/xdp-synproxy/README.org @@ -0,0 +1,29 @@ +#+Title: XDP SYNPROXY sample application + +This is a sample application for XDP SYNPROXY. It was cloned from +the Linux source code tree under tools/testing/selftests/bpf and called +xdp_synproxy. main purpose of it is to demonstrate capabilities of +XDP accelerating SYN Proxying for SYN flood DDOS protection. It is +a real practical example for user to use. For an overview of accelerating +SYNPROXY WITH XDP, Please refer to this paper +(https://netdevconf.info/0x15/slides/30/Netdev%200x15%20Accelerating%20synproxy%20with%20XDP.pdf) + +Note XDP SYNPROXY requires netfilter connection tracking and here are the +sysctl knobs and iptables rules preparation for XDP SYNPROXY: +#+BEGIN_SRC sh + sudo sysctl -w net.ipv4.tcp_syncookies=2 + sudo sysctl -w net.ipv4.tcp_timestamps=1 + sudo sysctl -w net.netfilter.nf_conntrack_tcp_loose=0 + sudo iptables -t raw -I PREROUTING -i -p tcp -m tcp --syn --dport -j CT --notrack + sudo iptables -t filter -A INPUT -i -p tcp -m tcp --dport -m state --state INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460 + sudo iptables -t filter -A INPUT -i -m state --state INVALID -j DROP +#+END_SRC + +Here is how to start the XDP SYNPROXY application: +#+BEGIN_SRC sh + sudo xdp_synproxy --iface --file --mss4 1460 --mss6 1440 --wscale 7 --ttl 254 --ports , +#+END_SRC + +XDP SYNPROXY can coexist with other XDP programs since we use libxdp +to attach the XDP SYNPROXY program, meaning you could build chain of +XDP programs and attach them to same network interface. diff --git a/xdp-synproxy/xdp_synproxy.c b/xdp-synproxy/xdp_synproxy.c new file mode 100644 index 0000000..758e85d --- /dev/null +++ b/xdp-synproxy/xdp_synproxy.c @@ -0,0 +1,388 @@ +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause +/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "logging.h" +#include "xdp_synproxy_kern.skel.h" + + +#define STRERR_BUFSIZE 1024 + +static unsigned int ifindex; +static __u32 attached_prog_id; + +static noreturn void cleanup() +{ + char errmsg[STRERR_BUFSIZE]; + struct xdp_program *p = NULL; + int err; + + if (attached_prog_id == 0) + exit(0); + + p = xdp_program__from_id(attached_prog_id); + + err = xdp_program__detach(p, ifindex, 0, 0); + xdp_program__close(p); + if (err) { + libxdp_strerror(err, errmsg, sizeof(errmsg)); + pr_warn("Couldn't detach BPF program: %s(%d)\n", errmsg, err); + p = NULL; + exit(1); + } + + exit(0); +} + +static noreturn void help(const char *progname) +{ + fprintf(stderr, "Usage: %s [--iface |--prog ] [--mss4 --mss6 --wscale --ttl ] [--ports ,,...]\n", + progname); + exit(1); +} + +static unsigned long parse_arg_ul(const char *progname, const char *arg, unsigned long limit) +{ + unsigned long res; + char *endptr; + + errno = 0; + res = strtoul(arg, &endptr, 10); + if (errno != 0 || *endptr != '\0' || arg[0] == '\0' || res > limit) + help(progname); + + return res; +} + +static void parse_options(int argc, char *argv[], unsigned int *ifindex, __u32 *prog_id, + __u64 *tcpipopts, char **ports) +{ + static struct option long_options[] = { + { "help", no_argument, NULL, 'h' }, + { "iface", required_argument, NULL, 'i' }, + { "prog", required_argument, NULL, 'x' }, + { "mss4", required_argument, NULL, 4 }, + { "mss6", required_argument, NULL, 6 }, + { "wscale", required_argument, NULL, 'w' }, + { "ttl", required_argument, NULL, 't' }, + { "ports", required_argument, NULL, 'p' }, + { NULL, 0, NULL, 0 }, + }; + unsigned long mss4, wscale, ttl; + unsigned long long mss6; + unsigned int tcpipopts_mask = 0; + + if (argc < 2) + help(argv[0]); + + *ifindex = 0; + *prog_id = 0; + *tcpipopts = 0; + *ports = NULL; + + while (true) { + int opt; + + opt = getopt_long(argc, argv, "", long_options, NULL); + if (opt == -1) + break; + + switch (opt) { + case 'h': + help(argv[0]); + break; + case 'i': + *ifindex = if_nametoindex(optarg); + if (*ifindex == 0) + help(argv[0]); + break; + case 'x': + *prog_id = parse_arg_ul(argv[0], optarg, UINT32_MAX); + if (*prog_id == 0) + help(argv[0]); + break; + case 4: + mss4 = parse_arg_ul(argv[0], optarg, UINT16_MAX); + tcpipopts_mask |= 1 << 0; + break; + case 6: + mss6 = parse_arg_ul(argv[0], optarg, UINT16_MAX); + tcpipopts_mask |= 1 << 1; + break; + case 'w': + wscale = parse_arg_ul(argv[0], optarg, 14); + tcpipopts_mask |= 1 << 2; + break; + case 't': + ttl = parse_arg_ul(argv[0], optarg, UINT8_MAX); + tcpipopts_mask |= 1 << 3; + break; + case 'p': + *ports = optarg; + break; + default: + help(argv[0]); + } + } + if (optind < argc) + help(argv[0]); + + if (tcpipopts_mask == 0xf) { + if (mss4 == 0 || mss6 == 0 || wscale == 0 || ttl == 0) + help(argv[0]); + *tcpipopts = (mss6 << 32) | (ttl << 24) | (wscale << 16) | mss4; + } else if (tcpipopts_mask != 0) { + help(argv[0]); + } + + if (*ifindex != 0 && *prog_id != 0) + help(argv[0]); + if (*ifindex == 0 && *prog_id == 0) + help(argv[0]); +} + +static int syncookie_attach(unsigned int ifindex) +{ + char errmsg[STRERR_BUFSIZE]; + struct xdp_program *p = NULL; + struct xdp_synproxy_kern *skel; + int err; + + char *xdp_program_name = "syncookie_xdp"; + DECLARE_LIBXDP_OPTS(xdp_program_opts, xdp_opts, 0); + + skel = xdp_synproxy_kern__open(); + if (!skel) { + err = -errno; + pr_warn("Couldn't open XDP program: %s\n", strerror(-err)); + return err; + } + + xdp_opts.obj = skel->obj; + xdp_opts.prog_name = xdp_program_name; + p = xdp_program__create(&xdp_opts); + err = libxdp_get_error(p); + if (err) { + libxdp_strerror(err, errmsg, sizeof(errmsg)); + pr_warn("Couldn't create xdp program: %s(%d)\n", errmsg, err); + goto out; + } + + err = xdp_program__attach(p, ifindex, 0, 0); + if (err) { + libxdp_strerror(err, errmsg, sizeof(errmsg)); + pr_warn("Couldn't attach BPF program: %s(%d)\n", errmsg, err); + goto out; + } + attached_prog_id = xdp_program__id(p); + + err = 0; + + signal(SIGINT, cleanup); + signal(SIGTERM, cleanup); + +out: + xdp_program__close(p); + xdp_synproxy_kern__destroy(skel); + return err; +} + +static int syncookie_open_bpf_maps(__u32 prog_id, int *values_map_fd, int *ports_map_fd) +{ + struct bpf_prog_info prog_info; + __u32 map_ids[8]; + __u32 info_len; + int prog_fd; + int err; + int i; + + *values_map_fd = -1; + *ports_map_fd = -1; + + prog_fd = bpf_prog_get_fd_by_id(prog_id); + if (prog_fd < 0) { + fprintf(stderr, "Error: bpf_prog_get_fd_by_id: %s\n", strerror(-prog_fd)); + return prog_fd; + } + + prog_info = (struct bpf_prog_info) { + .nr_map_ids = 8, + .map_ids = (__u64)(unsigned long)map_ids, + }; + info_len = sizeof(prog_info); + + err = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &info_len); + if (err != 0) { + fprintf(stderr, "Error: bpf_prog_get_info_by_fd: %s\n", + strerror(-err)); + goto out; + } + + if (prog_info.nr_map_ids < 2) { + fprintf(stderr, "Error: Found %u BPF maps, expected at least 2\n", + prog_info.nr_map_ids); + err = -ENOENT; + goto out; + } + + for (i = 0; i < (int)prog_info.nr_map_ids; i++) { + struct bpf_map_info map_info = {}; + int map_fd; + + err = bpf_map_get_fd_by_id(map_ids[i]); + if (err < 0) { + fprintf(stderr, "Error: bpf_map_get_fd_by_id: %s\n", strerror(-err)); + goto err_close_map_fds; + } + map_fd = err; + + info_len = sizeof(map_info); + err = bpf_obj_get_info_by_fd(map_fd, &map_info, &info_len); + if (err != 0) { + fprintf(stderr, "Error: bpf_map_get_info_by_fd: %s\n", + strerror(-err)); + close(map_fd); + goto err_close_map_fds; + } + if (strcmp(map_info.name, "values") == 0) { + *values_map_fd = map_fd; + continue; + } + if (strcmp(map_info.name, "allowed_ports") == 0) { + *ports_map_fd = map_fd; + continue; + } + close(map_fd); + } + + if (*values_map_fd != -1 && *ports_map_fd != -1) { + err = 0; + goto out; + } + + err = -ENOENT; + +err_close_map_fds: + if (*values_map_fd != -1) + close(*values_map_fd); + if (*ports_map_fd != -1) + close(*ports_map_fd); + *values_map_fd = -1; + *ports_map_fd = -1; + +out: + close(prog_fd); + return err; +} + +int main(int argc, char *argv[]) +{ + int values_map_fd, ports_map_fd; + __u64 tcpipopts; + bool firstiter; + __u64 prevcnt; + __u32 prog_id; + char *ports; + int err = 0; + + parse_options(argc, argv, &ifindex, &prog_id, &tcpipopts, &ports); + + if (prog_id == 0) { + err = syncookie_attach(ifindex); + if (err < 0) + goto out; + prog_id = attached_prog_id; + } + + err = syncookie_open_bpf_maps(prog_id, &values_map_fd, &ports_map_fd); + if (err < 0) + goto out; + + if (ports) { + __u16 port_last = 0; + __u32 port_idx = 0; + char *p = ports; + + fprintf(stderr, "Replacing allowed ports\n"); + + while (p && *p != '\0') { + char *token = strsep(&p, ","); + __u16 port; + + port = parse_arg_ul(argv[0], token, UINT16_MAX); + err = bpf_map_update_elem(ports_map_fd, &port_idx, &port, BPF_ANY); + if (err != 0) { + fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err)); + fprintf(stderr, "Failed to add port %u (index %u)\n", + port, port_idx); + goto out_close_maps; + } + fprintf(stderr, "Added port %u\n", port); + port_idx++; + } + err = bpf_map_update_elem(ports_map_fd, &port_idx, &port_last, BPF_ANY); + if (err != 0) { + fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err)); + fprintf(stderr, "Failed to add the terminator value 0 (index %u)\n", + port_idx); + goto out_close_maps; + } + } + + if (tcpipopts) { + __u32 key = 0; + + fprintf(stderr, "Replacing TCP/IP options\n"); + + err = bpf_map_update_elem(values_map_fd, &key, &tcpipopts, BPF_ANY); + if (err != 0) { + fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err)); + goto out_close_maps; + } + } + + if ((ports || tcpipopts) && attached_prog_id == 0) + goto out_close_maps; + + prevcnt = 0; + firstiter = true; + while (true) { + __u32 key = 1; + __u64 value; + + err = bpf_map_lookup_elem(values_map_fd, &key, &value); + if (err != 0) { + fprintf(stderr, "Error: bpf_map_lookup_elem: %s\n", strerror(-err)); + goto out_close_maps; + } + if (firstiter) { + prevcnt = value; + firstiter = false; + } + printf("SYNACKs generated: %llu (total %llu)\n", value - prevcnt, value); + prevcnt = value; + sleep(1); + } + +out_close_maps: + close(values_map_fd); + close(ports_map_fd); +out: + return err == 0 ? 0 : 1; +} diff --git a/xdp-synproxy/xdp_synproxy_kern.c b/xdp-synproxy/xdp_synproxy_kern.c new file mode 100644 index 0000000..e38e5a8 --- /dev/null +++ b/xdp-synproxy/xdp_synproxy_kern.c @@ -0,0 +1,801 @@ +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause +/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */ + +#include "vmlinux_local.h" + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#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 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 { + int netns_id; + int 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 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(__u32 saddr, __u32 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 unroll + for (i = 0; i < 4; i++) + sum += (__u32)saddr->in6_u.u6_addr32[i]; + +#pragma 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_time_stamp_raw(void) +{ + return tcp_ns_to_ts(tcp_clock_ns()); +} + +struct tcpopt_context { + __u8 *ptr; + __u8 *end; + void *data_end; + __be32 *tsecr; + __u8 wscale; + bool option_timestamp; + bool option_sack; +}; + +static int tscookie_tcpopt_parse(struct tcpopt_context *ctx) +{ + __u8 opcode, opsize; + + if (ctx->ptr >= ctx->end) + return 1; + if (ctx->ptr >= ctx->data_end) + return 1; + + opcode = ctx->ptr[0]; + + if (opcode == TCPOPT_EOL) + return 1; + if (opcode == TCPOPT_NOP) { + ++ctx->ptr; + return 0; + } + + if (ctx->ptr + 1 >= ctx->end) + return 1; + if (ctx->ptr + 1 >= ctx->data_end) + return 1; + opsize = ctx->ptr[1]; + if (opsize < 2) + return 1; + + if (ctx->ptr + opsize > ctx->end) + return 1; + + switch (opcode) { + case TCPOPT_WINDOW: + if (opsize == TCPOLEN_WINDOW && ctx->ptr + TCPOLEN_WINDOW <= ctx->data_end) + ctx->wscale = ctx->ptr[2] < TCP_MAX_WSCALE ? ctx->ptr[2] : TCP_MAX_WSCALE; + break; + case TCPOPT_TIMESTAMP: + if (opsize == TCPOLEN_TIMESTAMP && ctx->ptr + TCPOLEN_TIMESTAMP <= ctx->data_end) { + ctx->option_timestamp = true; + /* Client's tsval becomes our tsecr. */ + *ctx->tsecr = get_unaligned((__be32 *)(ctx->ptr + 2)); + } + break; + case TCPOPT_SACK_PERM: + if (opsize == TCPOLEN_SACK_PERM) + ctx->option_sack = true; + break; + } + + ctx->ptr += 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_end) +{ + struct tcpopt_context loop_ctx = { + .ptr = (__u8 *)(tcp_header + 1), + .end = (__u8 *)tcp_header + tcp_len, + .data_end = data_end, + .tsecr = tsecr, + .wscale = TS_OPT_WSCALE_MASK, + .option_timestamp = false, + .option_sack = false, + }; + __u32 cookie; + + bpf_loop(6, tscookie_tcpopt_parse_batch, &loop_ctx, 0); + + if (!loop_ctx.option_timestamp) + return false; + + cookie = tcp_time_stamp_raw() & ~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; + } + + ct = bpf_xdp_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_BIT) + return XDP_PASS; + } else if (ct_lookup_opts.error != -ENOENT) { + return XDP_ABORTED; + } + + /* error == -ENOENT || !(status & IPS_CONFIRMED_BIT) */ + 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) +{ + __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; + + 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_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 (bpf_xdp_adjust_tail(ctx, new_pkt_size - old_pkt_size)) + 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; + + /* Pass to upper stack if port requires no syncookie handling */ + if (!check_port_allowed(bpf_ntohs(hdr->tcp->dest))) + return XDP_PASS; + + /* 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; + } + + return XDP_TX; +} + +static __always_inline int syncookie_part2(void *ctx, void *data, void *data_end, + struct header_pointers *hdr) +{ + 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) : + 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); +} + +char _license[] SEC("license") = "GPL";