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Message-ID: <7e04fc5f-30a9-468e-bf07-49b00040b6db@linux.dev>
Date: Tue, 5 Dec 2023 22:39:33 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org,
netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH v4 bpf-next 3/3] selftest: bpf: Test
bpf_sk_assign_tcp_reqsk().
On 12/4/23 5:34 PM, Kuniyuki Iwashima wrote:
> This commit adds a sample selftest to demonstrate how we can use
> bpf_sk_assign_tcp_reqsk() as the backend of SYN Proxy.
>
> The test creates IPv4/IPv6 x TCP/MPTCP connections and transfer
> messages over them on lo with BPF tc prog attached.
>
> The tc prog will process SYN and returns SYN+ACK with the following
> ISN and TS. In a real use case, this part will be done by other
> hosts.
>
> MSB LSB
> ISN: | 31 ... 8 | 7 6 | 5 | 4 | 3 2 1 0 |
> | Hash_1 | MSS | ECN | SACK | WScale |
>
> TS: | 31 ... 8 | 7 ... 0 |
> | Random | Hash_2 |
Thanks for the details. It is helpful.
>
> WScale in SYN is reused in SYN+ACK.
>
> The client returns ACK, and tc prog will recalculate ISN and TS
> from ACK and validate SYN Cookie.
>
> If it's valid, the prog calls kfunc to allocate a reqsk for skb and
> configure the reqsk based on the argument created from SYN Cookie.
>
> Later, the reqsk will be processed in cookie_v[46]_check() to create
> a connection.
>
[ ... ]
> +SEC("tc")
> +int tcp_custom_syncookie(struct __sk_buff *skb)
> +{
> + struct tcp_syncookie ctx = {
> + .skb = skb,
> + };
> +
> + if (tcp_load_headers(&ctx))
> + return TC_ACT_OK;
> +
> + if (ctx.tcp->rst)
> + return TC_ACT_OK;
> +
> + if (ctx.tcp->syn) {
> + if (ctx.tcp->ack)
> + return TC_ACT_OK;
> +
> + return tcp_handle_syn(&ctx);
> + }
> +
> + return tcp_handle_ack(&ctx);
It may be useful to ensure tcp_handle_{syn,ack} is executed instead of the
kernel doing the regular syncookie. A global variable (bool or counter) can be
used by the prog_tests to check.
> +}
> +
> +char _license[] SEC("license") = "GPL";
> diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.h b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.h
> new file mode 100644
> index 000000000000..a401f59e46d8
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.h
> @@ -0,0 +1,162 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright Amazon.com Inc. or its affiliates. */
> +
> +#ifndef _TEST_TCP_SYNCOOKIE_H
> +#define _TEST_TCP_SYNCOOKIE_H
> +
> +#define TC_ACT_OK 0
> +#define TC_ACT_SHOT 2
> +
> +#define ETH_ALEN 6
> +#define ETH_P_IP 0x0800
> +#define ETH_P_IPV6 0x86DD
> +
> +#define NEXTHDR_TCP 6
> +
> +#define TCPOPT_NOP 1
> +#define TCPOPT_EOL 0
> +#define TCPOPT_MSS 2
> +#define TCPOPT_WINDOW 3
> +#define TCPOPT_TIMESTAMP 8
> +#define TCPOPT_SACK_PERM 4
> +
> +#define TCPOLEN_MSS 4
> +#define TCPOLEN_WINDOW 3
> +#define TCPOLEN_TIMESTAMP 10
> +#define TCPOLEN_SACK_PERM 2
Some of the above is already in the bpf_tracing_net.h. Move the non-existing
ones to bpf_tracing_net.h also.
> +#define BPF_F_CURRENT_NETNS (-1)
This should be already in the vmlinux.h
> +
> +#define __packed __attribute__((__packed__))
> +#define __force
> +
> +#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
> +
> +#define swap(a, b) \
> + do { \
> + typeof(a) __tmp = (a); \
> + (a) = (b); \
> + (b) = __tmp; \
> + } while (0)
> +
> +#define swap_array(a, b) \
> + do { \
> + typeof(a) __tmp[sizeof(a)]; \
> + __builtin_memcpy(__tmp, a, sizeof(a)); \
> + __builtin_memcpy(a, b, sizeof(a)); \
> + __builtin_memcpy(b, __tmp, sizeof(a)); \
> + } while (0)
> +
> +/* asm-generic/unaligned.h */
> +#define __get_unaligned_t(type, ptr) ({ \
> + const struct { type x; } __packed * __pptr = (typeof(__pptr))(ptr); \
> + __pptr->x; \
> +})
> +
> +#define get_unaligned(ptr) __get_unaligned_t(typeof(*(ptr)), (ptr))
> +
> +static inline u16 get_unaligned_be16(const void *p)
> +{
> + return bpf_ntohs(__get_unaligned_t(__be16, p));
> +}
> +
> +static inline u32 get_unaligned_be32(const void *p)
> +{
> + return bpf_ntohl(__get_unaligned_t(__be32, p));
> +}
> +
> +/* lib/checksum.c */
> +static inline u32 from64to32(u64 x)
> +{
> + /* add up 32-bit and 32-bit for 32+c bit */
> + x = (x & 0xffffffff) + (x >> 32);
> + /* add up carry.. */
> + x = (x & 0xffffffff) + (x >> 32);
> + return (u32)x;
> +}
> +
> +static inline __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
> + __u32 len, __u8 proto, __wsum sum)
> +{
> + unsigned long long s = (__force u32)sum;
> +
> + s += (__force u32)saddr;
> + s += (__force u32)daddr;
> +#ifdef __BIG_ENDIAN
> + s += proto + len;
> +#else
> + s += (proto + len) << 8;
> +#endif
> + return (__force __wsum)from64to32(s);
> +}
> +
> +/* asm-generic/checksum.h */
> +static inline __sum16 csum_fold(__wsum csum)
> +{
> + u32 sum = (__force u32)csum;
> +
> + sum = (sum & 0xffff) + (sum >> 16);
> + sum = (sum & 0xffff) + (sum >> 16);
> + return (__force __sum16)~sum;
> +}
> +
> +static inline __sum16 csum_tcpudp_magic(__be32 saddr, __be32 daddr, __u32 len,
> + __u8 proto, __wsum sum)
> +{
> + return csum_fold(csum_tcpudp_nofold(saddr, daddr, len, proto, sum));
> +}
> +
> +/* net/ipv6/ip6_checksum.c */
> +static inline __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
> + const struct in6_addr *daddr,
> + __u32 len, __u8 proto, __wsum csum)
> +{
> + int carry;
> + __u32 ulen;
> + __u32 uproto;
> + __u32 sum = (__force u32)csum;
> +
> + sum += (__force u32)saddr->in6_u.u6_addr32[0];
> + carry = (sum < (__force u32)saddr->in6_u.u6_addr32[0]);
> + sum += carry;
> +
> + sum += (__force u32)saddr->in6_u.u6_addr32[1];
> + carry = (sum < (__force u32)saddr->in6_u.u6_addr32[1]);
> + sum += carry;
> +
> + sum += (__force u32)saddr->in6_u.u6_addr32[2];
> + carry = (sum < (__force u32)saddr->in6_u.u6_addr32[2]);
> + sum += carry;
> +
> + sum += (__force u32)saddr->in6_u.u6_addr32[3];
> + carry = (sum < (__force u32)saddr->in6_u.u6_addr32[3]);
> + sum += carry;
> +
> + sum += (__force u32)daddr->in6_u.u6_addr32[0];
> + carry = (sum < (__force u32)daddr->in6_u.u6_addr32[0]);
> + sum += carry;
> +
> + sum += (__force u32)daddr->in6_u.u6_addr32[1];
> + carry = (sum < (__force u32)daddr->in6_u.u6_addr32[1]);
> + sum += carry;
> +
> + sum += (__force u32)daddr->in6_u.u6_addr32[2];
> + carry = (sum < (__force u32)daddr->in6_u.u6_addr32[2]);
> + sum += carry;
> +
> + sum += (__force u32)daddr->in6_u.u6_addr32[3];
> + carry = (sum < (__force u32)daddr->in6_u.u6_addr32[3]);
> + sum += carry;
> +
> + ulen = (__force u32)bpf_htonl((__u32)len);
> + sum += ulen;
> + carry = (sum < ulen);
> + sum += carry;
> +
> + uproto = (__force u32)bpf_htonl(proto);
> + sum += uproto;
> + carry = (sum < uproto);
> + sum += carry;
> +
> + return csum_fold((__force __wsum)sum);
> +}
The above helpers are useful for other tests, so make sense to stay in
test_tcp_custom_syncookie.h. e.g. In the future, some of the duplicated helpers
in xdp_synproxy_kern.c can be removed.
> +#endif
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