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

#include <linux/stddef.h>
#include <linux/bpf.h>
#include <sys/socket.h>

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

#include <bpf_sockopt_helpers.h>

#define SRC_REWRITE_IP6_0       0
#define SRC_REWRITE_IP6_1       0
#define SRC_REWRITE_IP6_2       0
#define SRC_REWRITE_IP6_3       6

#define DST_REWRITE_IP6_0       0
#define DST_REWRITE_IP6_1       0
#define DST_REWRITE_IP6_2       0
#define DST_REWRITE_IP6_3       1

#define DST_REWRITE_IP6_V4_MAPPED_0     0
#define DST_REWRITE_IP6_V4_MAPPED_1     0
#define DST_REWRITE_IP6_V4_MAPPED_2     0x0000FFFF
#define DST_REWRITE_IP6_V4_MAPPED_3     0xc0a80004 // 192.168.0.4

#define DST_REWRITE_PORT6       6666

SEC("cgroup/sendmsg6")
int sendmsg_v6_prog(struct bpf_sock_addr *ctx)
{
        if (ctx->type != SOCK_DGRAM)
                return 0;

        if (!get_set_sk_priority(ctx))
                return 0;

        /* Rewrite source. */
        if (ctx->msg_src_ip6[3] == bpf_htonl(1) ||
            ctx->msg_src_ip6[3] == bpf_htonl(0)) {
                ctx->msg_src_ip6[0] = bpf_htonl(SRC_REWRITE_IP6_0);
                ctx->msg_src_ip6[1] = bpf_htonl(SRC_REWRITE_IP6_1);
                ctx->msg_src_ip6[2] = bpf_htonl(SRC_REWRITE_IP6_2);
                ctx->msg_src_ip6[3] = bpf_htonl(SRC_REWRITE_IP6_3);
        } else {
                /* Unexpected source. Reject sendmsg. */
                return 0;
        }

        /* Rewrite destination. */
        if (ctx->user_ip6[0] == bpf_htonl(0xFACEB00C)) {
                ctx->user_ip6[0] = bpf_htonl(DST_REWRITE_IP6_0);
                ctx->user_ip6[1] = bpf_htonl(DST_REWRITE_IP6_1);
                ctx->user_ip6[2] = bpf_htonl(DST_REWRITE_IP6_2);
                ctx->user_ip6[3] = bpf_htonl(DST_REWRITE_IP6_3);

                ctx->user_port = bpf_htons(DST_REWRITE_PORT6);
        } else {
                /* Unexpected destination. Reject sendmsg. */
                return 0;
        }

        return 1;
}

SEC("cgroup/sendmsg6")
int sendmsg_v6_v4mapped_prog(struct bpf_sock_addr *ctx)
{
        /* Rewrite source. */
        ctx->msg_src_ip6[0] = bpf_htonl(SRC_REWRITE_IP6_0);
        ctx->msg_src_ip6[1] = bpf_htonl(SRC_REWRITE_IP6_1);
        ctx->msg_src_ip6[2] = bpf_htonl(SRC_REWRITE_IP6_2);
        ctx->msg_src_ip6[3] = bpf_htonl(SRC_REWRITE_IP6_3);

        /* Rewrite destination. */
        ctx->user_ip6[0] = bpf_htonl(DST_REWRITE_IP6_V4_MAPPED_0);
        ctx->user_ip6[1] = bpf_htonl(DST_REWRITE_IP6_V4_MAPPED_1);
        ctx->user_ip6[2] = bpf_htonl(DST_REWRITE_IP6_V4_MAPPED_2);
        ctx->user_ip6[3] = bpf_htonl(DST_REWRITE_IP6_V4_MAPPED_3);

        ctx->user_port = bpf_htons(DST_REWRITE_PORT6);

        return 1;
}

SEC("cgroup/sendmsg6")
int sendmsg_v6_wildcard_prog(struct bpf_sock_addr *ctx)
{
        /* Rewrite source. */
        ctx->msg_src_ip6[0] = bpf_htonl(SRC_REWRITE_IP6_0);
        ctx->msg_src_ip6[1] = bpf_htonl(SRC_REWRITE_IP6_1);
        ctx->msg_src_ip6[2] = bpf_htonl(SRC_REWRITE_IP6_2);
        ctx->msg_src_ip6[3] = bpf_htonl(SRC_REWRITE_IP6_3);

        /* Rewrite destination. */
        ctx->user_ip6[0] = bpf_htonl(0);
        ctx->user_ip6[1] = bpf_htonl(0);
        ctx->user_ip6[2] = bpf_htonl(0);
        ctx->user_ip6[3] = bpf_htonl(0);

        ctx->user_port = bpf_htons(DST_REWRITE_PORT6);

        return 1;
}

SEC("cgroup/sendmsg6")
int sendmsg_v6_preserve_dst_prog(struct bpf_sock_addr *ctx)
{
        return 1;
}

SEC("cgroup/sendmsg6")
int sendmsg_v6_deny_prog(struct bpf_sock_addr *ctx)
{
        return 0;
}

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