844 lines
20 KiB
C
844 lines
20 KiB
C
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// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
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/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_endian.h>
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#include <asm/errno.h>
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#define TC_ACT_OK 0
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#define TC_ACT_SHOT 2
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#define NSEC_PER_SEC 1000000000L
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#define ETH_ALEN 6
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#define ETH_P_IP 0x0800
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#define ETH_P_IPV6 0x86DD
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#define tcp_flag_word(tp) (((union tcp_word_hdr *)(tp))->words[3])
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#define IP_DF 0x4000
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#define IP_MF 0x2000
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#define IP_OFFSET 0x1fff
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#define NEXTHDR_TCP 6
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#define TCPOPT_NOP 1
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#define TCPOPT_EOL 0
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#define TCPOPT_MSS 2
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#define TCPOPT_WINDOW 3
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#define TCPOPT_SACK_PERM 4
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#define TCPOPT_TIMESTAMP 8
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#define TCPOLEN_MSS 4
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#define TCPOLEN_WINDOW 3
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#define TCPOLEN_SACK_PERM 2
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#define TCPOLEN_TIMESTAMP 10
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#define TCP_TS_HZ 1000
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#define TS_OPT_WSCALE_MASK 0xf
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#define TS_OPT_SACK (1 << 4)
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#define TS_OPT_ECN (1 << 5)
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#define TSBITS 6
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#define TSMASK (((__u32)1 << TSBITS) - 1)
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#define TCP_MAX_WSCALE 14U
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#define IPV4_MAXLEN 60
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#define TCP_MAXLEN 60
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#define DEFAULT_MSS4 1460
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#define DEFAULT_MSS6 1440
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#define DEFAULT_WSCALE 7
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#define DEFAULT_TTL 64
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#define MAX_ALLOWED_PORTS 8
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#define swap(a, b) \
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do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
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#define __get_unaligned_t(type, ptr) ({ \
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const struct { type x; } __attribute__((__packed__)) *__pptr = (typeof(__pptr))(ptr); \
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__pptr->x; \
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})
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#define get_unaligned(ptr) __get_unaligned_t(typeof(*(ptr)), (ptr))
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struct {
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__uint(type, BPF_MAP_TYPE_ARRAY);
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__type(key, __u32);
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__type(value, __u64);
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__uint(max_entries, 2);
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} values SEC(".maps");
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struct {
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__uint(type, BPF_MAP_TYPE_ARRAY);
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__type(key, __u32);
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__type(value, __u16);
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__uint(max_entries, MAX_ALLOWED_PORTS);
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} allowed_ports SEC(".maps");
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/* Some symbols defined in net/netfilter/nf_conntrack_bpf.c are unavailable in
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* vmlinux.h if CONFIG_NF_CONNTRACK=m, so they are redefined locally.
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*/
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struct bpf_ct_opts___local {
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s32 netns_id;
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s32 error;
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u8 l4proto;
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u8 dir;
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u8 reserved[2];
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} __attribute__((preserve_access_index));
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#define BPF_F_CURRENT_NETNS (-1)
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extern struct nf_conn *bpf_xdp_ct_lookup(struct xdp_md *xdp_ctx,
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struct bpf_sock_tuple *bpf_tuple,
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__u32 len_tuple,
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struct bpf_ct_opts___local *opts,
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__u32 len_opts) __ksym;
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extern struct nf_conn *bpf_skb_ct_lookup(struct __sk_buff *skb_ctx,
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struct bpf_sock_tuple *bpf_tuple,
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u32 len_tuple,
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struct bpf_ct_opts___local *opts,
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u32 len_opts) __ksym;
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extern void bpf_ct_release(struct nf_conn *ct) __ksym;
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static __always_inline void swap_eth_addr(__u8 *a, __u8 *b)
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{
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__u8 tmp[ETH_ALEN];
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__builtin_memcpy(tmp, a, ETH_ALEN);
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__builtin_memcpy(a, b, ETH_ALEN);
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__builtin_memcpy(b, tmp, ETH_ALEN);
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}
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static __always_inline __u16 csum_fold(__u32 csum)
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{
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csum = (csum & 0xffff) + (csum >> 16);
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csum = (csum & 0xffff) + (csum >> 16);
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return (__u16)~csum;
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}
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static __always_inline __u16 csum_tcpudp_magic(__be32 saddr, __be32 daddr,
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__u32 len, __u8 proto,
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__u32 csum)
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{
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__u64 s = csum;
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s += (__u32)saddr;
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s += (__u32)daddr;
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#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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s += proto + len;
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#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
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s += (proto + len) << 8;
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#else
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#error Unknown endian
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#endif
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s = (s & 0xffffffff) + (s >> 32);
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s = (s & 0xffffffff) + (s >> 32);
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return csum_fold((__u32)s);
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}
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static __always_inline __u16 csum_ipv6_magic(const struct in6_addr *saddr,
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const struct in6_addr *daddr,
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__u32 len, __u8 proto, __u32 csum)
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{
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__u64 sum = csum;
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int i;
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#pragma unroll
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for (i = 0; i < 4; i++)
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sum += (__u32)saddr->in6_u.u6_addr32[i];
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#pragma unroll
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for (i = 0; i < 4; i++)
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sum += (__u32)daddr->in6_u.u6_addr32[i];
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/* Don't combine additions to avoid 32-bit overflow. */
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sum += bpf_htonl(len);
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sum += bpf_htonl(proto);
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sum = (sum & 0xffffffff) + (sum >> 32);
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sum = (sum & 0xffffffff) + (sum >> 32);
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return csum_fold((__u32)sum);
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}
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static __always_inline __u64 tcp_clock_ns(void)
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{
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return bpf_ktime_get_ns();
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}
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static __always_inline __u32 tcp_ns_to_ts(__u64 ns)
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{
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return ns / (NSEC_PER_SEC / TCP_TS_HZ);
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}
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static __always_inline __u32 tcp_time_stamp_raw(void)
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{
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return tcp_ns_to_ts(tcp_clock_ns());
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}
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struct tcpopt_context {
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__u8 *ptr;
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__u8 *end;
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void *data_end;
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__be32 *tsecr;
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__u8 wscale;
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bool option_timestamp;
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bool option_sack;
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};
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static int tscookie_tcpopt_parse(struct tcpopt_context *ctx)
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{
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__u8 opcode, opsize;
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if (ctx->ptr >= ctx->end)
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return 1;
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if (ctx->ptr >= ctx->data_end)
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return 1;
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opcode = ctx->ptr[0];
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if (opcode == TCPOPT_EOL)
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return 1;
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if (opcode == TCPOPT_NOP) {
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++ctx->ptr;
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return 0;
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}
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if (ctx->ptr + 1 >= ctx->end)
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return 1;
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if (ctx->ptr + 1 >= ctx->data_end)
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return 1;
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opsize = ctx->ptr[1];
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if (opsize < 2)
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return 1;
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if (ctx->ptr + opsize > ctx->end)
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return 1;
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switch (opcode) {
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case TCPOPT_WINDOW:
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if (opsize == TCPOLEN_WINDOW && ctx->ptr + TCPOLEN_WINDOW <= ctx->data_end)
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ctx->wscale = ctx->ptr[2] < TCP_MAX_WSCALE ? ctx->ptr[2] : TCP_MAX_WSCALE;
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break;
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case TCPOPT_TIMESTAMP:
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if (opsize == TCPOLEN_TIMESTAMP && ctx->ptr + TCPOLEN_TIMESTAMP <= ctx->data_end) {
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ctx->option_timestamp = true;
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/* Client's tsval becomes our tsecr. */
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*ctx->tsecr = get_unaligned((__be32 *)(ctx->ptr + 2));
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}
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break;
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case TCPOPT_SACK_PERM:
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if (opsize == TCPOLEN_SACK_PERM)
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ctx->option_sack = true;
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break;
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}
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ctx->ptr += opsize;
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return 0;
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}
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static int tscookie_tcpopt_parse_batch(__u32 index, void *context)
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{
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int i;
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for (i = 0; i < 7; i++)
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if (tscookie_tcpopt_parse(context))
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return 1;
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return 0;
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}
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static __always_inline bool tscookie_init(struct tcphdr *tcp_header,
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__u16 tcp_len, __be32 *tsval,
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__be32 *tsecr, void *data_end)
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{
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struct tcpopt_context loop_ctx = {
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.ptr = (__u8 *)(tcp_header + 1),
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.end = (__u8 *)tcp_header + tcp_len,
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.data_end = data_end,
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.tsecr = tsecr,
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.wscale = TS_OPT_WSCALE_MASK,
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.option_timestamp = false,
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.option_sack = false,
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};
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u32 cookie;
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bpf_loop(6, tscookie_tcpopt_parse_batch, &loop_ctx, 0);
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if (!loop_ctx.option_timestamp)
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return false;
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cookie = tcp_time_stamp_raw() & ~TSMASK;
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cookie |= loop_ctx.wscale & TS_OPT_WSCALE_MASK;
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if (loop_ctx.option_sack)
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cookie |= TS_OPT_SACK;
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if (tcp_header->ece && tcp_header->cwr)
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cookie |= TS_OPT_ECN;
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*tsval = bpf_htonl(cookie);
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return true;
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}
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static __always_inline void values_get_tcpipopts(__u16 *mss, __u8 *wscale,
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__u8 *ttl, bool ipv6)
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{
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__u32 key = 0;
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__u64 *value;
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value = bpf_map_lookup_elem(&values, &key);
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if (value && *value != 0) {
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if (ipv6)
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*mss = (*value >> 32) & 0xffff;
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else
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*mss = *value & 0xffff;
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*wscale = (*value >> 16) & 0xf;
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*ttl = (*value >> 24) & 0xff;
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return;
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}
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*mss = ipv6 ? DEFAULT_MSS6 : DEFAULT_MSS4;
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*wscale = DEFAULT_WSCALE;
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*ttl = DEFAULT_TTL;
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}
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static __always_inline void values_inc_synacks(void)
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{
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__u32 key = 1;
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__u64 *value;
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value = bpf_map_lookup_elem(&values, &key);
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if (value)
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__sync_fetch_and_add(value, 1);
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}
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static __always_inline bool check_port_allowed(__u16 port)
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{
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__u32 i;
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for (i = 0; i < MAX_ALLOWED_PORTS; i++) {
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__u32 key = i;
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__u16 *value;
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value = bpf_map_lookup_elem(&allowed_ports, &key);
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if (!value)
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break;
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/* 0 is a terminator value. Check it first to avoid matching on
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* a forbidden port == 0 and returning true.
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*/
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if (*value == 0)
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break;
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if (*value == port)
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return true;
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}
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return false;
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}
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struct header_pointers {
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struct ethhdr *eth;
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struct iphdr *ipv4;
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struct ipv6hdr *ipv6;
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struct tcphdr *tcp;
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__u16 tcp_len;
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};
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static __always_inline int tcp_dissect(void *data, void *data_end,
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struct header_pointers *hdr)
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{
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hdr->eth = data;
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if (hdr->eth + 1 > data_end)
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return XDP_DROP;
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switch (bpf_ntohs(hdr->eth->h_proto)) {
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case ETH_P_IP:
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hdr->ipv6 = NULL;
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hdr->ipv4 = (void *)hdr->eth + sizeof(*hdr->eth);
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if (hdr->ipv4 + 1 > data_end)
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return XDP_DROP;
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if (hdr->ipv4->ihl * 4 < sizeof(*hdr->ipv4))
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return XDP_DROP;
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if (hdr->ipv4->version != 4)
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return XDP_DROP;
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if (hdr->ipv4->protocol != IPPROTO_TCP)
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return XDP_PASS;
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hdr->tcp = (void *)hdr->ipv4 + hdr->ipv4->ihl * 4;
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break;
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case ETH_P_IPV6:
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hdr->ipv4 = NULL;
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hdr->ipv6 = (void *)hdr->eth + sizeof(*hdr->eth);
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if (hdr->ipv6 + 1 > data_end)
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return XDP_DROP;
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if (hdr->ipv6->version != 6)
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return XDP_DROP;
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/* XXX: Extension headers are not supported and could circumvent
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* XDP SYN flood protection.
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*/
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if (hdr->ipv6->nexthdr != NEXTHDR_TCP)
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return XDP_PASS;
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hdr->tcp = (void *)hdr->ipv6 + sizeof(*hdr->ipv6);
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break;
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default:
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/* XXX: VLANs will circumvent XDP SYN flood protection. */
|
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return XDP_PASS;
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}
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if (hdr->tcp + 1 > data_end)
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return XDP_DROP;
|
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hdr->tcp_len = hdr->tcp->doff * 4;
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if (hdr->tcp_len < sizeof(*hdr->tcp))
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return XDP_DROP;
|
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return XDP_TX;
|
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}
|
||
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|
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static __always_inline int tcp_lookup(void *ctx, struct header_pointers *hdr, bool xdp)
|
||
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{
|
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struct bpf_ct_opts___local ct_lookup_opts = {
|
||
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.netns_id = BPF_F_CURRENT_NETNS,
|
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.l4proto = IPPROTO_TCP,
|
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};
|
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struct bpf_sock_tuple tup = {};
|
||
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struct nf_conn *ct;
|
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__u32 tup_size;
|
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|
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if (hdr->ipv4) {
|
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/* TCP doesn't normally use fragments, and XDP can't reassemble
|
||
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* them.
|
||
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*/
|
||
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if ((hdr->ipv4->frag_off & bpf_htons(IP_DF | IP_MF | IP_OFFSET)) != bpf_htons(IP_DF))
|
||
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return XDP_DROP;
|
||
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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_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,
|
||
|
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_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";
|