// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
#define BPF_NO_KFUNC_PROTOTYPES
#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";
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