// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2020 Facebook */

#include <stddef.h>
#include <errno.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/tcp.h>
#include <linux/socket.h>
#include <linux/bpf.h>
#include <linux/types.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#define BPF_PROG_TEST_TCP_HDR_OPTIONS
#include "test_tcp_hdr_options.h"
#include "bpf_misc.h"

__u8 test_kind = TCPOPT_EXP;
__u16 test_magic = 0xeB9F;
__u32 inherit_cb_flags = 0;

struct bpf_test_option passive_synack_out = {};
struct bpf_test_option passive_fin_out  = {};

struct bpf_test_option passive_estab_in = {};
struct bpf_test_option passive_fin_in   = {};

struct bpf_test_option active_syn_out   = {};
struct bpf_test_option active_fin_out   = {};

struct bpf_test_option active_estab_in  = {};
struct bpf_test_option active_fin_in    = {};

struct {
        __uint(type, BPF_MAP_TYPE_SK_STORAGE);
        __uint(map_flags, BPF_F_NO_PREALLOC);
        __type(key, int);
        __type(value, struct hdr_stg);
} hdr_stg_map SEC(".maps");

static bool skops_want_cookie(const struct bpf_sock_ops *skops)
{
        return skops->args[0] == BPF_WRITE_HDR_TCP_SYNACK_COOKIE;
}

static bool skops_current_mss(const struct bpf_sock_ops *skops)
{
        return skops->args[0] == BPF_WRITE_HDR_TCP_CURRENT_MSS;
}

static __u8 option_total_len(__u8 flags)
{
        __u8 i, len = 1; /* +1 for flags */

        if (!flags)
                return 0;

        /* RESEND bit does not use a byte */
        for (i = OPTION_RESEND + 1; i < __NR_OPTION_FLAGS; i++)
                len += !!TEST_OPTION_FLAGS(flags, i);

        if (test_kind == TCPOPT_EXP)
                return len + TCP_BPF_EXPOPT_BASE_LEN;
        else
                return len + 2; /* +1 kind, +1 kind-len */
}

static void write_test_option(const struct bpf_test_option *test_opt,
                              __u8 *data)
{
        __u8 offset = 0;

        data[offset++] = test_opt->flags;
        if (TEST_OPTION_FLAGS(test_opt->flags, OPTION_MAX_DELACK_MS))
                data[offset++] = test_opt->max_delack_ms;

        if (TEST_OPTION_FLAGS(test_opt->flags, OPTION_RAND))
                data[offset++] = test_opt->rand;
}

static int store_option(struct bpf_sock_ops *skops,
                        const struct bpf_test_option *test_opt)
{
        union {
                struct tcp_exprm_opt exprm;
                struct tcp_opt regular;
        } write_opt;
        int err;

        if (test_kind == TCPOPT_EXP) {
                write_opt.exprm.kind = TCPOPT_EXP;
                write_opt.exprm.len = option_total_len(test_opt->flags);
                write_opt.exprm.magic = __bpf_htons(test_magic);
                write_opt.exprm.data32 = 0;
                write_test_option(test_opt, write_opt.exprm.data);
                err = bpf_store_hdr_opt(skops, &write_opt.exprm,
                                        sizeof(write_opt.exprm), 0);
        } else {
                write_opt.regular.kind = test_kind;
                write_opt.regular.len = option_total_len(test_opt->flags);
                write_opt.regular.data32 = 0;
                write_test_option(test_opt, write_opt.regular.data);
                err = bpf_store_hdr_opt(skops, &write_opt.regular,
                                        sizeof(write_opt.regular), 0);
        }

        if (err)
                RET_CG_ERR(err);

        return CG_OK;
}

static int parse_test_option(struct bpf_test_option *opt, const __u8 *start)
{
        opt->flags = *start++;

        if (TEST_OPTION_FLAGS(opt->flags, OPTION_MAX_DELACK_MS))
                opt->max_delack_ms = *start++;

        if (TEST_OPTION_FLAGS(opt->flags, OPTION_RAND))
                opt->rand = *start++;

        return 0;
}

static int load_option(struct bpf_sock_ops *skops,
                       struct bpf_test_option *test_opt, bool from_syn)
{
        union {
                struct tcp_exprm_opt exprm;
                struct tcp_opt regular;
        } search_opt;
        int ret, load_flags = from_syn ? BPF_LOAD_HDR_OPT_TCP_SYN : 0;

        if (test_kind == TCPOPT_EXP) {
                search_opt.exprm.kind = TCPOPT_EXP;
                search_opt.exprm.len = 4;
                search_opt.exprm.magic = __bpf_htons(test_magic);
                search_opt.exprm.data32 = 0;
                ret = bpf_load_hdr_opt(skops, &search_opt.exprm,
                                       sizeof(search_opt.exprm), load_flags);
                if (ret < 0)
                        return ret;
                return parse_test_option(test_opt, search_opt.exprm.data);
        } else {
                search_opt.regular.kind = test_kind;
                search_opt.regular.len = 0;
                search_opt.regular.data32 = 0;
                ret = bpf_load_hdr_opt(skops, &search_opt.regular,
                                       sizeof(search_opt.regular), load_flags);
                if (ret < 0)
                        return ret;
                return parse_test_option(test_opt, search_opt.regular.data);
        }
}

static int synack_opt_len(struct bpf_sock_ops *skops)
{
        struct bpf_test_option test_opt = {};
        __u8 optlen;
        int err;

        if (!passive_synack_out.flags)
                return CG_OK;

        err = load_option(skops, &test_opt, true);

        /* bpf_test_option is not found */
        if (err == -ENOMSG)
                return CG_OK;

        if (err)
                RET_CG_ERR(err);

        optlen = option_total_len(passive_synack_out.flags);
        if (optlen) {
                err = bpf_reserve_hdr_opt(skops, optlen, 0);
                if (err)
                        RET_CG_ERR(err);
        }

        return CG_OK;
}

static int write_synack_opt(struct bpf_sock_ops *skops)
{
        struct bpf_test_option opt;

        if (!passive_synack_out.flags)
                /* We should not even be called since no header
                 * space has been reserved.
                 */
                RET_CG_ERR(0);

        opt = passive_synack_out;
        if (skops_want_cookie(skops))
                SET_OPTION_FLAGS(opt.flags, OPTION_RESEND);

        return store_option(skops, &opt);
}

static int syn_opt_len(struct bpf_sock_ops *skops)
{
        __u8 optlen;
        int err;

        if (!active_syn_out.flags)
                return CG_OK;

        optlen = option_total_len(active_syn_out.flags);
        if (optlen) {
                err = bpf_reserve_hdr_opt(skops, optlen, 0);
                if (err)
                        RET_CG_ERR(err);
        }

        return CG_OK;
}

static int write_syn_opt(struct bpf_sock_ops *skops)
{
        if (!active_syn_out.flags)
                RET_CG_ERR(0);

        return store_option(skops, &active_syn_out);
}

static int fin_opt_len(struct bpf_sock_ops *skops)
{
        struct bpf_test_option *opt;
        struct hdr_stg *hdr_stg;
        __u8 optlen;
        int err;

        if (!skops->sk)
                RET_CG_ERR(0);

        hdr_stg = bpf_sk_storage_get(&hdr_stg_map, skops->sk, NULL, 0);
        if (!hdr_stg)
                RET_CG_ERR(0);

        if (hdr_stg->active)
                opt = &active_fin_out;
        else
                opt = &passive_fin_out;

        optlen = option_total_len(opt->flags);
        if (optlen) {
                err = bpf_reserve_hdr_opt(skops, optlen, 0);
                if (err)
                        RET_CG_ERR(err);
        }

        return CG_OK;
}

static int write_fin_opt(struct bpf_sock_ops *skops)
{
        struct bpf_test_option *opt;
        struct hdr_stg *hdr_stg;

        if (!skops->sk)
                RET_CG_ERR(0);

        hdr_stg = bpf_sk_storage_get(&hdr_stg_map, skops->sk, NULL, 0);
        if (!hdr_stg)
                RET_CG_ERR(0);

        if (hdr_stg->active)
                opt = &active_fin_out;
        else
                opt = &passive_fin_out;

        if (!opt->flags)
                RET_CG_ERR(0);

        return store_option(skops, opt);
}

static int resend_in_ack(struct bpf_sock_ops *skops)
{
        struct hdr_stg *hdr_stg;

        if (!skops->sk)
                return -1;

        hdr_stg = bpf_sk_storage_get(&hdr_stg_map, skops->sk, NULL, 0);
        if (!hdr_stg)
                return -1;

        return !!hdr_stg->resend_syn;
}

static int nodata_opt_len(struct bpf_sock_ops *skops)
{
        int resend;

        resend = resend_in_ack(skops);
        if (resend < 0)
                RET_CG_ERR(0);

        if (resend)
                return syn_opt_len(skops);

        return CG_OK;
}

static int write_nodata_opt(struct bpf_sock_ops *skops)
{
        int resend;

        resend = resend_in_ack(skops);
        if (resend < 0)
                RET_CG_ERR(0);

        if (resend)
                return write_syn_opt(skops);

        return CG_OK;
}

static int data_opt_len(struct bpf_sock_ops *skops)
{
        /* Same as the nodata version.  Mostly to show
         * an example usage on skops->skb_len.
         */
        return nodata_opt_len(skops);
}

static int write_data_opt(struct bpf_sock_ops *skops)
{
        return write_nodata_opt(skops);
}

static int current_mss_opt_len(struct bpf_sock_ops *skops)
{
        /* Reserve maximum that may be needed */
        int err;

        err = bpf_reserve_hdr_opt(skops, option_total_len(OPTION_MASK), 0);
        if (err)
                RET_CG_ERR(err);

        return CG_OK;
}

static int handle_hdr_opt_len(struct bpf_sock_ops *skops)
{
        __u8 tcp_flags = skops_tcp_flags(skops);

        if ((tcp_flags & TCPHDR_SYNACK) == TCPHDR_SYNACK)
                return synack_opt_len(skops);

        if (tcp_flags & TCPHDR_SYN)
                return syn_opt_len(skops);

        if (tcp_flags & TCPHDR_FIN)
                return fin_opt_len(skops);

        if (skops_current_mss(skops))
                /* The kernel is calculating the MSS */
                return current_mss_opt_len(skops);

        if (skops->skb_len)
                return data_opt_len(skops);

        return nodata_opt_len(skops);
}

static int handle_write_hdr_opt(struct bpf_sock_ops *skops)
{
        __u8 tcp_flags = skops_tcp_flags(skops);
        struct tcphdr *th;

        if ((tcp_flags & TCPHDR_SYNACK) == TCPHDR_SYNACK)
                return write_synack_opt(skops);

        if (tcp_flags & TCPHDR_SYN)
                return write_syn_opt(skops);

        if (tcp_flags & TCPHDR_FIN)
                return write_fin_opt(skops);

        th = skops->skb_data;
        if (th + 1 > skops->skb_data_end)
                RET_CG_ERR(0);

        if (skops->skb_len > tcp_hdrlen(th))
                return write_data_opt(skops);

        return write_nodata_opt(skops);
}

static int set_delack_max(struct bpf_sock_ops *skops, __u8 max_delack_ms)
{
        __u32 max_delack_us = max_delack_ms * 1000;

        return bpf_setsockopt(skops, SOL_TCP, TCP_BPF_DELACK_MAX,
                              &max_delack_us, sizeof(max_delack_us));
}

static int set_rto_min(struct bpf_sock_ops *skops, __u8 peer_max_delack_ms)
{
        __u32 min_rto_us = peer_max_delack_ms * 1000;

        return bpf_setsockopt(skops, SOL_TCP, TCP_BPF_RTO_MIN, &min_rto_us,
                              sizeof(min_rto_us));
}

static int handle_active_estab(struct bpf_sock_ops *skops)
{
        struct hdr_stg init_stg = {
                .active = true,
        };
        int err;

        err = load_option(skops, &active_estab_in, false);
        if (err && err != -ENOMSG)
                RET_CG_ERR(err);

        init_stg.resend_syn = TEST_OPTION_FLAGS(active_estab_in.flags,
                                                OPTION_RESEND);
        if (!skops->sk || !bpf_sk_storage_get(&hdr_stg_map, skops->sk,
                                              &init_stg,
                                              BPF_SK_STORAGE_GET_F_CREATE))
                RET_CG_ERR(0);

        if (init_stg.resend_syn)
                /* Don't clear the write_hdr cb now because
                 * the ACK may get lost and retransmit may
                 * be needed.
                 *
                 * PARSE_ALL_HDR cb flag is set to learn if this
                 * resend_syn option has received by the peer.
                 *
                 * The header option will be resent until a valid
                 * packet is received at handle_parse_hdr()
                 * and all hdr cb flags will be cleared in
                 * handle_parse_hdr().
                 */
                set_parse_all_hdr_cb_flags(skops);
        else if (!active_fin_out.flags)
                /* No options will be written from now */
                clear_hdr_cb_flags(skops);

        if (active_syn_out.max_delack_ms) {
                err = set_delack_max(skops, active_syn_out.max_delack_ms);
                if (err)
                        RET_CG_ERR(err);
        }

        if (active_estab_in.max_delack_ms) {
                err = set_rto_min(skops, active_estab_in.max_delack_ms);
                if (err)
                        RET_CG_ERR(err);
        }

        return CG_OK;
}

static int handle_passive_estab(struct bpf_sock_ops *skops)
{
        struct hdr_stg init_stg = {};
        struct tcphdr *th;
        int err;

        inherit_cb_flags = skops->bpf_sock_ops_cb_flags;

        err = load_option(skops, &passive_estab_in, true);
        if (err == -ENOENT) {
                /* saved_syn is not found. It was in syncookie mode.
                 * We have asked the active side to resend the options
                 * in ACK, so try to find the bpf_test_option from ACK now.
                 */
                err = load_option(skops, &passive_estab_in, false);
                init_stg.syncookie = true;
        }

        /* ENOMSG: The bpf_test_option is not found which is fine.
         * Bail out now for all other errors.
         */
        if (err && err != -ENOMSG)
                RET_CG_ERR(err);

        th = skops->skb_data;
        if (th + 1 > skops->skb_data_end)
                RET_CG_ERR(0);

        if (th->syn) {
                /* Fastopen */

                /* Cannot clear cb_flags to stop write_hdr cb.
                 * synack is not sent yet for fast open.
                 * Even it was, the synack may need to be retransmitted.
                 *
                 * PARSE_ALL_HDR cb flag is set to learn
                 * if synack has reached the peer.
                 * All cb_flags will be cleared in handle_parse_hdr().
                 */
                set_parse_all_hdr_cb_flags(skops);
                init_stg.fastopen = true;
        } else if (!passive_fin_out.flags) {
                /* No options will be written from now */
                clear_hdr_cb_flags(skops);
        }

        if (!skops->sk ||
            !bpf_sk_storage_get(&hdr_stg_map, skops->sk, &init_stg,
                                BPF_SK_STORAGE_GET_F_CREATE))
                RET_CG_ERR(0);

        if (passive_synack_out.max_delack_ms) {
                err = set_delack_max(skops, passive_synack_out.max_delack_ms);
                if (err)
                        RET_CG_ERR(err);
        }

        if (passive_estab_in.max_delack_ms) {
                err = set_rto_min(skops, passive_estab_in.max_delack_ms);
                if (err)
                        RET_CG_ERR(err);
        }

        return CG_OK;
}

static int handle_parse_hdr(struct bpf_sock_ops *skops)
{
        struct hdr_stg *hdr_stg;
        struct tcphdr *th;

        if (!skops->sk)
                RET_CG_ERR(0);

        th = skops->skb_data;
        if (th + 1 > skops->skb_data_end)
                RET_CG_ERR(0);

        hdr_stg = bpf_sk_storage_get(&hdr_stg_map, skops->sk, NULL, 0);
        if (!hdr_stg)
                RET_CG_ERR(0);

        if (hdr_stg->resend_syn || hdr_stg->fastopen)
                /* The PARSE_ALL_HDR cb flag was turned on
                 * to ensure that the previously written
                 * options have reached the peer.
                 * Those previously written option includes:
                 *     - Active side: resend_syn in ACK during syncookie
                 *      or
                 *     - Passive side: SYNACK during fastopen
                 *
                 * A valid packet has been received here after
                 * the 3WHS, so the PARSE_ALL_HDR cb flag
                 * can be cleared now.
                 */
                clear_parse_all_hdr_cb_flags(skops);

        if (hdr_stg->resend_syn && !active_fin_out.flags)
                /* Active side resent the syn option in ACK
                 * because the server was in syncookie mode.
                 * A valid packet has been received, so
                 * clear header cb flags if there is no
                 * more option to send.
                 */
                clear_hdr_cb_flags(skops);

        if (hdr_stg->fastopen && !passive_fin_out.flags)
                /* Passive side was in fastopen.
                 * A valid packet has been received, so
                 * the SYNACK has reached the peer.
                 * Clear header cb flags if there is no more
                 * option to send.
                 */
                clear_hdr_cb_flags(skops);

        if (th->fin) {
                struct bpf_test_option *fin_opt;
                int err;

                if (hdr_stg->active)
                        fin_opt = &active_fin_in;
                else
                        fin_opt = &passive_fin_in;

                err = load_option(skops, fin_opt, false);
                if (err && err != -ENOMSG)
                        RET_CG_ERR(err);
        }

        return CG_OK;
}

SEC("sockops")
int estab(struct bpf_sock_ops *skops)
{
        int true_val = 1;

        switch (skops->op) {
        case BPF_SOCK_OPS_TCP_LISTEN_CB:
                bpf_setsockopt(skops, SOL_TCP, TCP_SAVE_SYN,
                               &true_val, sizeof(true_val));
                set_hdr_cb_flags(skops, BPF_SOCK_OPS_STATE_CB_FLAG);
                break;
        case BPF_SOCK_OPS_TCP_CONNECT_CB:
                set_hdr_cb_flags(skops, 0);
                break;
        case BPF_SOCK_OPS_PARSE_HDR_OPT_CB:
                return handle_parse_hdr(skops);
        case BPF_SOCK_OPS_HDR_OPT_LEN_CB:
                return handle_hdr_opt_len(skops);
        case BPF_SOCK_OPS_WRITE_HDR_OPT_CB:
                return handle_write_hdr_opt(skops);
        case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
                return handle_passive_estab(skops);
        case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
                return handle_active_estab(skops);
        }

        return CG_OK;
}

char _license[] SEC("license") = "GPL";