Re: [PATCH bpf-next v9 3/5] bpf: Add helpers to issue and check SYN cookies in XDP

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, May 3, 2022 at 10:15 AM Maxim Mikityanskiy <maximmi@nvidia.com> wrote:
>
> The new helpers bpf_tcp_raw_{gen,check}_syncookie_ipv{4,6} allow an XDP
> program to generate SYN cookies in response to TCP SYN packets and to
> check those cookies upon receiving the first ACK packet (the final
> packet of the TCP handshake).
>
> Unlike bpf_tcp_{gen,check}_syncookie these new helpers don't need a
> listening socket on the local machine, which allows to use them together
> with synproxy to accelerate SYN cookie generation.
>
> Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
> Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
> ---
>  include/net/tcp.h              |   1 +
>  include/uapi/linux/bpf.h       |  78 ++++++++++++++++++++++
>  net/core/filter.c              | 118 +++++++++++++++++++++++++++++++++
>  net/ipv4/tcp_input.c           |   3 +-
>  scripts/bpf_doc.py             |   4 ++
>  tools/include/uapi/linux/bpf.h |  78 ++++++++++++++++++++++
>  6 files changed, 281 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 94a52ad1101c..45aafc28ce00 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -432,6 +432,7 @@ u16 tcp_v4_get_syncookie(struct sock *sk, struct iphdr *iph,
>                          struct tcphdr *th, u32 *cookie);
>  u16 tcp_v6_get_syncookie(struct sock *sk, struct ipv6hdr *iph,
>                          struct tcphdr *th, u32 *cookie);
> +u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss);
>  u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
>                           const struct tcp_request_sock_ops *af_ops,
>                           struct sock *sk, struct tcphdr *th);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4dd9e34f2a60..5e611d898302 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5156,6 +5156,80 @@ union bpf_attr {
>   *             if not NULL, is a reference which must be released using its
>   *             corresponding release function, or moved into a BPF map before
>   *             program exit.
> + *
> + * s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th, u32 th_len)
> + *     Description
> + *             Try to issue a SYN cookie for the packet with corresponding
> + *             IPv4/TCP headers, *iph* and *th*, without depending on a
> + *             listening socket.
> + *
> + *             *iph* points to the IPv4 header.
> + *
> + *             *th* points to the start of the TCP header, while *th_len*
> + *             contains the length of the TCP header (at least
> + *             **sizeof**\ (**struct tcphdr**)).
> + *     Return
> + *             On success, lower 32 bits hold the generated SYN cookie in
> + *             followed by 16 bits which hold the MSS value for that cookie,
> + *             and the top 16 bits are unused.
> + *
> + *             On failure, the returned value is one of the following:
> + *
> + *             **-EINVAL** if *th_len* is invalid.
> + *
> + * s64 bpf_tcp_raw_gen_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th, u32 th_len)
> + *     Description
> + *             Try to issue a SYN cookie for the packet with corresponding
> + *             IPv6/TCP headers, *iph* and *th*, without depending on a
> + *             listening socket.
> + *
> + *             *iph* points to the IPv6 header.
> + *
> + *             *th* points to the start of the TCP header, while *th_len*
> + *             contains the length of the TCP header (at least
> + *             **sizeof**\ (**struct tcphdr**)).
> + *     Return
> + *             On success, lower 32 bits hold the generated SYN cookie in
> + *             followed by 16 bits which hold the MSS value for that cookie,
> + *             and the top 16 bits are unused.
> + *
> + *             On failure, the returned value is one of the following:
> + *
> + *             **-EINVAL** if *th_len* is invalid.
> + *
> + *             **-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
> + *
> + * int bpf_tcp_raw_check_syncookie_ipv4(struct iphdr *iph, struct tcphdr *th)

Note that all existing helpers that just return error or 0 on success
return long. Please use long for consistency.

> + *     Description
> + *             Check whether *iph* and *th* contain a valid SYN cookie ACK
> + *             without depending on a listening socket.
> + *
> + *             *iph* points to the IPv4 header.
> + *
> + *             *th* points to the TCP header.
> + *     Return
> + *             0 if *iph* and *th* are a valid SYN cookie ACK.
> + *
> + *             On failure, the returned value is one of the following:
> + *
> + *             **-EACCES** if the SYN cookie is not valid.
> + *
> + * int bpf_tcp_raw_check_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr *th)

same

> + *     Description
> + *             Check whether *iph* and *th* contain a valid SYN cookie ACK
> + *             without depending on a listening socket.
> + *
> + *             *iph* points to the IPv6 header.
> + *
> + *             *th* points to the TCP header.
> + *     Return
> + *             0 if *iph* and *th* are a valid SYN cookie ACK.
> + *
> + *             On failure, the returned value is one of the following:
> + *
> + *             **-EACCES** if the SYN cookie is not valid.
> + *
> + *             **-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.

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