int dns_packet_read_uint8(DnsPacket *p, uint8_t *ret, size_t *start) {
        const void *d;
        int r;

        assert(p);

        r = dns_packet_read(p, sizeof(uint8_t), &d, start);
        if (r < 0)
                return r;

        *ret = ((uint8_t*) d)[0];
        return 0;
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.