// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2018 Facebook

#include <string.h>

#include <linux/stddef.h>
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/in6.h>
#include <linux/tcp.h>
#include <linux/if.h>
#include <errno.h>

#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

#define SRC_REWRITE_IP4         0x7f000004U
#define DST_REWRITE_IP4         0x7f000001U
#define DST_REWRITE_PORT4       4444

#ifndef TCP_CA_NAME_MAX
#define TCP_CA_NAME_MAX 16
#endif

#ifndef TCP_NOTSENT_LOWAT
#define TCP_NOTSENT_LOWAT 25
#endif

#ifndef IFNAMSIZ
#define IFNAMSIZ 16
#endif

#ifndef SOL_TCP
#define SOL_TCP 6
#endif

const char reno[] = "reno";
const char cubic[] = "cubic";

__attribute__ ((noinline)) __weak
int do_bind(struct bpf_sock_addr *ctx)
{
        struct sockaddr_in sa = {};

        sa.sin_family = AF_INET;
        sa.sin_port = bpf_htons(0);
        sa.sin_addr.s_addr = bpf_htonl(SRC_REWRITE_IP4);

        if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
                return 0;

        return 1;
}

static __inline int verify_cc(struct bpf_sock_addr *ctx,
                              const char expected[])
{
        char buf[TCP_CA_NAME_MAX];

        if (bpf_getsockopt(ctx, SOL_TCP, TCP_CONGESTION, &buf, sizeof(buf)))
                return 1;

        if (bpf_strncmp(buf, TCP_CA_NAME_MAX, expected))
                return 1;

        return 0;
}

static __inline int set_cc(struct bpf_sock_addr *ctx)
{
        if (bpf_setsockopt(ctx, SOL_TCP, TCP_CONGESTION, (void *)reno, sizeof(reno)))
                return 1;
        if (verify_cc(ctx, reno))
                return 1;

        if (bpf_setsockopt(ctx, SOL_TCP, TCP_CONGESTION, (void *)cubic, sizeof(cubic)))
                return 1;
        if (verify_cc(ctx, cubic))
                return 1;

        return 0;
}

static __inline int bind_to_device(struct bpf_sock_addr *ctx)
{
        char veth1[IFNAMSIZ] = "test_sock_addr1";
        char veth2[IFNAMSIZ] = "test_sock_addr2";
        char missing[IFNAMSIZ] = "nonexistent_dev";
        char del_bind[IFNAMSIZ] = "";

        if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
                                &veth1, sizeof(veth1)))
                return 1;
        if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
                                &veth2, sizeof(veth2)))
                return 1;
        if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
                                &missing, sizeof(missing)) != -ENODEV)
                return 1;
        if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
                                &del_bind, sizeof(del_bind)))
                return 1;

        return 0;
}

static __inline int set_keepalive(struct bpf_sock_addr *ctx)
{
        int zero = 0, one = 1;

        if (bpf_setsockopt(ctx, SOL_SOCKET, SO_KEEPALIVE, &one, sizeof(one)))
                return 1;
        if (ctx->type == SOCK_STREAM) {
                if (bpf_setsockopt(ctx, SOL_TCP, TCP_KEEPIDLE, &one, sizeof(one)))
                        return 1;
                if (bpf_setsockopt(ctx, SOL_TCP, TCP_KEEPINTVL, &one, sizeof(one)))
                        return 1;
                if (bpf_setsockopt(ctx, SOL_TCP, TCP_KEEPCNT, &one, sizeof(one)))
                        return 1;
                if (bpf_setsockopt(ctx, SOL_TCP, TCP_SYNCNT, &one, sizeof(one)))
                        return 1;
                if (bpf_setsockopt(ctx, SOL_TCP, TCP_USER_TIMEOUT, &one, sizeof(one)))
                        return 1;
        }
        if (bpf_setsockopt(ctx, SOL_SOCKET, SO_KEEPALIVE, &zero, sizeof(zero)))
                return 1;

        return 0;
}

static __inline int set_notsent_lowat(struct bpf_sock_addr *ctx)
{
        int lowat = 65535;

        if (ctx->type == SOCK_STREAM) {
                if (bpf_setsockopt(ctx, SOL_TCP, TCP_NOTSENT_LOWAT, &lowat, sizeof(lowat)))
                        return 1;
        }

        return 0;
}

SEC("cgroup/connect4")
int connect_v4_prog(struct bpf_sock_addr *ctx)
{
        struct bpf_sock_tuple tuple = {};
        struct bpf_sock *sk;

        /* Verify that new destination is available. */
        memset(&tuple.ipv4.saddr, 0, sizeof(tuple.ipv4.saddr));
        memset(&tuple.ipv4.sport, 0, sizeof(tuple.ipv4.sport));

        tuple.ipv4.daddr = bpf_htonl(DST_REWRITE_IP4);
        tuple.ipv4.dport = bpf_htons(DST_REWRITE_PORT4);

        /* Bind to device and unbind it. */
        if (bind_to_device(ctx))
                return 0;

        if (set_keepalive(ctx))
                return 0;

        if (set_notsent_lowat(ctx))
                return 0;

        if (ctx->type != SOCK_STREAM && ctx->type != SOCK_DGRAM)
                return 0;
        else if (ctx->type == SOCK_STREAM)
                sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof(tuple.ipv4),
                                       BPF_F_CURRENT_NETNS, 0);
        else
                sk = bpf_sk_lookup_udp(ctx, &tuple, sizeof(tuple.ipv4),
                                       BPF_F_CURRENT_NETNS, 0);

        if (!sk)
                return 0;

        if (sk->src_ip4 != tuple.ipv4.daddr ||
            sk->src_port != DST_REWRITE_PORT4) {
                bpf_sk_release(sk);
                return 0;
        }

        bpf_sk_release(sk);

        /* Rewrite congestion control. */
        if (ctx->type == SOCK_STREAM && set_cc(ctx))
                return 0;

        /* Rewrite destination. */
        ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
        ctx->user_port = bpf_htons(DST_REWRITE_PORT4);

        return do_bind(ctx) ? 1 : 0;
}

SEC("cgroup/connect4")
int connect_v4_deny_prog(struct bpf_sock_addr *ctx)
{
        return 0;
}

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