DRiKE

static __always_inline
int udp_dns_reply(struct cursor *c)
{
    struct udphdr  *udp;
    struct dnshdr  *dns;
 
    if (!(udp = parse_udphdr(c))|| udp->dest != __bpf_htons(DNS_PORT)
    ||  !(dns = parse_dnshdr(c)))
        return -1;
 

DRiKE

 // continuing:

    if (dns->arcount) {
        struct dns_rr  *opt_rr;
        uint8_t        *opt_owner = c->pos;
 
        opt_owner = c->pos;
        if (++c->pos > c->end || *opt_owner
        || !(opt_rr = parse_dns_rr(c))
        ||   opt_rr->type != __bpf_htons(RR_TYPE_OPT))

DRiKE

static __always_inline
void csum_remove_data(uint32_t *csum, struct cursor *c, uint16_t len)
{
    if (c->pos + len <= c->end) {
        *csum = bpf_csum_diff(c->pos, len, 0, 0, *csum);
        c->pos += len;
    }
}

int xdp_dns_says_no(struct xdp_md *ctx)