testprogs/fuzz/fuzz_filter.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <pcap/pcap.h>

void fuzz_openFile(const char * name){
    //do nothing
}

int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
    pcap_t * pkts;
    struct bpf_program bpf;
    char * filter;

    //we need at least 1 byte for linktype
    if (Size < 1) {
        return 0;
    }

    //initialize structure snaplen = 65535
    pkts = pcap_open_dead(Data[Size-1], 0xFFFF);
    if (pkts == NULL) {
        printf("pcap_open_dead failed\n");
        return 0;
    }
    filter = malloc(Size);
    memcpy(filter, Data, Size);
    //null terminate string
    filter[Size-1] = 0;

    if (pcap_compile(pkts, &bpf, filter, 1, PCAP_NETMASK_UNKNOWN) == 0) {
        pcap_setfilter(pkts, &bpf);
        pcap_close(pkts);
        pcap_freecode(&bpf);
    }
    else {
        pcap_close(pkts);
    }
    free(filter);

    return 0;
}