// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2020 Jesper Dangaard Brouer */

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <linux/if_ether.h>

#include <stddef.h>
#include <stdint.h>
#include <errno.h>

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

/* Userspace will update with MTU it can see on device */
volatile const int GLOBAL_USER_MTU;
volatile const __u32 GLOBAL_USER_IFINDEX;

/* BPF-prog will update these with MTU values it can see */
__u32 global_bpf_mtu_xdp = 0;
__u32 global_bpf_mtu_tc  = 0;

SEC("xdp")
int xdp_use_helper_basic(struct xdp_md *ctx)
{
        __u32 mtu_len = 0;

        if (bpf_check_mtu(ctx, 0, &mtu_len, 0, 0))
                return XDP_ABORTED;

        return XDP_PASS;
}

SEC("xdp")
int xdp_use_helper(struct xdp_md *ctx)
{
        int retval = XDP_PASS; /* Expected retval on successful test */
        __u32 mtu_len = 0;
        __u32 ifindex = 0;
        int delta = 0;

        /* When ifindex is zero, save net_device lookup and use ctx netdev */
        if (GLOBAL_USER_IFINDEX > 0)
                ifindex = GLOBAL_USER_IFINDEX;

        if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0)) {
                /* mtu_len is also valid when check fail */
                retval = XDP_ABORTED;
                goto out;
        }

        if (mtu_len != GLOBAL_USER_MTU)
                retval = XDP_DROP;

out:
        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("xdp")
int xdp_exceed_mtu(struct xdp_md *ctx)
{
        void *data_end = (void *)(long)ctx->data_end;
        void *data = (void *)(long)ctx->data;
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        __u32 data_len = data_end - data;
        int retval = XDP_ABORTED; /* Fail */
        __u32 mtu_len = 0;
        int delta;
        int err;

        /* Exceed MTU with 1 via delta adjust */
        delta = GLOBAL_USER_MTU - (data_len - ETH_HLEN) + 1;

        err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0);
        if (err) {
                retval = XDP_PASS; /* Success in exceeding MTU check */
                if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
                        retval = XDP_DROP;
        }

        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("xdp")
int xdp_minus_delta(struct xdp_md *ctx)
{
        int retval = XDP_PASS; /* Expected retval on successful test */
        void *data_end = (void *)(long)ctx->data_end;
        void *data = (void *)(long)ctx->data;
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        __u32 data_len = data_end - data;
        __u32 mtu_len = 0;
        int delta;

        /* Borderline test case: Minus delta exceeding packet length allowed */
        delta = -((data_len - ETH_HLEN) + 1);

        /* Minus length (adjusted via delta) still pass MTU check, other helpers
         * are responsible for catching this, when doing actual size adjust
         */
        if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))
                retval = XDP_ABORTED;

        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("xdp")
int xdp_input_len(struct xdp_md *ctx)
{
        int retval = XDP_PASS; /* Expected retval on successful test */
        void *data_end = (void *)(long)ctx->data_end;
        void *data = (void *)(long)ctx->data;
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        __u32 data_len = data_end - data;

        /* API allow user give length to check as input via mtu_len param,
         * resulting MTU value is still output in mtu_len param after call.
         *
         * Input len is L3, like MTU and iph->tot_len.
         * Remember XDP data_len is L2.
         */
        __u32 mtu_len = data_len - ETH_HLEN;

        if (bpf_check_mtu(ctx, ifindex, &mtu_len, 0, 0))
                retval = XDP_ABORTED;

        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("xdp")
int xdp_input_len_exceed(struct xdp_md *ctx)
{
        int retval = XDP_ABORTED; /* Fail */
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        int err;

        /* API allow user give length to check as input via mtu_len param,
         * resulting MTU value is still output in mtu_len param after call.
         *
         * Input length value is L3 size like MTU.
         */
        __u32 mtu_len = GLOBAL_USER_MTU;

        mtu_len += 1; /* Exceed with 1 */

        err = bpf_check_mtu(ctx, ifindex, &mtu_len, 0, 0);
        if (err == BPF_MTU_CHK_RET_FRAG_NEEDED)
                retval = XDP_PASS ; /* Success in exceeding MTU check */

        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("tc")
int tc_use_helper(struct __sk_buff *ctx)
{
        int retval = BPF_OK; /* Expected retval on successful test */
        __u32 mtu_len = 0;
        int delta = 0;

        if (bpf_check_mtu(ctx, 0, &mtu_len, delta, 0)) {
                retval = BPF_DROP;
                goto out;
        }

        if (mtu_len != GLOBAL_USER_MTU)
                retval = BPF_REDIRECT;
out:
        global_bpf_mtu_tc = mtu_len;
        return retval;
}

SEC("tc")
int tc_exceed_mtu(struct __sk_buff *ctx)
{
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        int retval = BPF_DROP; /* Fail */
        __u32 skb_len = ctx->len;
        __u32 mtu_len = 0;
        int delta;
        int err;

        /* Exceed MTU with 1 via delta adjust */
        delta = GLOBAL_USER_MTU - (skb_len - ETH_HLEN) + 1;

        err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0);
        if (err) {
                retval = BPF_OK; /* Success in exceeding MTU check */
                if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
                        retval = BPF_DROP;
        }

        global_bpf_mtu_tc = mtu_len;
        return retval;
}

SEC("tc")
int tc_exceed_mtu_da(struct __sk_buff *ctx)
{
        /* SKB Direct-Access variant */
        void *data_end = (void *)(long)ctx->data_end;
        void *data = (void *)(long)ctx->data;
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        __u32 data_len = data_end - data;
        int retval = BPF_DROP; /* Fail */
        __u32 mtu_len = 0;
        int delta;
        int err;

        /* Exceed MTU with 1 via delta adjust */
        delta = GLOBAL_USER_MTU - (data_len - ETH_HLEN) + 1;

        err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0);
        if (err) {
                retval = BPF_OK; /* Success in exceeding MTU check */
                if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
                        retval = BPF_DROP;
        }

        global_bpf_mtu_tc = mtu_len;
        return retval;
}

SEC("tc")
int tc_minus_delta(struct __sk_buff *ctx)
{
        int retval = BPF_OK; /* Expected retval on successful test */
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        __u32 skb_len = ctx->len;
        __u32 mtu_len = 0;
        int delta;

        /* Borderline test case: Minus delta exceeding packet length allowed */
        delta = -((skb_len - ETH_HLEN) + 1);

        /* Minus length (adjusted via delta) still pass MTU check, other helpers
         * are responsible for catching this, when doing actual size adjust
         */
        if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))
                retval = BPF_DROP;

        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("tc")
int tc_input_len(struct __sk_buff *ctx)
{
        int retval = BPF_OK; /* Expected retval on successful test */
        __u32 ifindex = GLOBAL_USER_IFINDEX;

        /* API allow user give length to check as input via mtu_len param,
         * resulting MTU value is still output in mtu_len param after call.
         *
         * Input length value is L3 size.
         */
        __u32 mtu_len = GLOBAL_USER_MTU;

        if (bpf_check_mtu(ctx, ifindex, &mtu_len, 0, 0))
                retval = BPF_DROP;

        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("tc")
int tc_input_len_exceed(struct __sk_buff *ctx)
{
        int retval = BPF_DROP; /* Fail */
        __u32 ifindex = GLOBAL_USER_IFINDEX;
        int err;

        /* API allow user give length to check as input via mtu_len param,
         * resulting MTU value is still output in mtu_len param after call.
         *
         * Input length value is L3 size like MTU.
         */
        __u32 mtu_len = GLOBAL_USER_MTU;

        mtu_len += 1; /* Exceed with 1 */

        err = bpf_check_mtu(ctx, ifindex, &mtu_len, 0, 0);
        if (err == BPF_MTU_CHK_RET_FRAG_NEEDED)
                retval = BPF_OK; /* Success in exceeding MTU check */

        global_bpf_mtu_xdp = mtu_len;
        return retval;
}

SEC("tc")
int tc_chk_segs_flag(struct __sk_buff *ctx)
{
        __u32 mtu_len = 0;
        int err;

        err = bpf_check_mtu(ctx, GLOBAL_USER_IFINDEX, &mtu_len, 0, BPF_MTU_CHK_SEGS);

        return err == -EINVAL ? BPF_OK : BPF_DROP;
}