droppacket_unsafe.c

// Copyright (c) eBPF for Windows contributors
// SPDX-License-Identifier: MIT

// clang -O2 -Werror -c droppacket_unsafe.c -o droppacket_unsafe_jit.o
//
// For bpf code: clang -target bpf -O2 -Werror -c droppacket_unsafe.c -o droppacket_unsafe.o
// this passes the checker

// Whenever this sample program changes, bpf2c_tests will fail unless the
// expected files in tests\bpf2c_tests\expected are updated. The following
// script can be used to regenerate the expected files:
//     generate_expected_bpf2c_output.ps1
//
// Usage:
// .\scripts\generate_expected_bpf2c_output.ps1 <build_output_path>
// Example:
// .\scripts\generate_expected_bpf2c_output.ps1 .\x64\Debug\

#include "bpf_endian.h"
#include "bpf_helpers.h"
#include "net/ip.h"
#include "net/udp.h"
#include "net_ebpf_ext_xdp_hooks.h"

struct
{
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __type(key, uint32_t);
    __type(value, uint64_t);
    __uint(max_entries, 1);
} port_map SEC(".maps");

SEC("xdp")
int
DropPacket(xdp_md_t* ctx)
{
    IPV4_HEADER* ip_header = (IPV4_HEADER*)ctx->data;
    UDP_HEADER* udp_header = (UDP_HEADER*)(ip_header + 1);
    int rc = XDP_PASS;

    // udp
    if (ip_header->Protocol == IPPROTO_UDP) {
        if (ntohs(udp_header->length) <= sizeof(UDP_HEADER)) {
            long key = 0;
            long* count = bpf_map_lookup_elem(&port_map, &key);
            if (count) {
                *count = (*count + 1);
            }
            rc = XDP_DROP;
        }
    }
    return rc;
}