static int dns_resolver_cmp(const struct key *key,
			    const struct key_match_data *match_data)
{
	int slen, dlen, ret = 0;
	const char *src = key->description, *dsp = match_data->raw_data;

	kenter("%s,%s", src, dsp);

	if (!src || !dsp)
		goto no_match;

	if (strcasecmp(src, dsp) == 0)
		goto matched;

	slen = strlen(src);
	dlen = strlen(dsp);
	if (slen <= 0 || dlen <= 0)
		goto no_match;
	if (src[slen - 1] == '.')
		slen--;
	if (dsp[dlen - 1] == '.')
		dlen--;
	if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
		goto no_match;

matched:
	ret = 1;
no_match:
	kleave(" = %d", ret);
	return ret;
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.