acc_ctx_cont(OM_uint32 *minstat,
	     gss_buffer_t buf,
	     gss_ctx_id_t *ctx,
	     gss_buffer_t *responseToken,
	     gss_buffer_t *mechListMIC,
	     OM_uint32 *negState,
	     send_token_flag *return_token)
{
	OM_uint32 ret, tmpmin;
	gss_OID supportedMech;
	spnego_gss_ctx_id_t sc;
	unsigned int len;
	unsigned char *ptr, *bufstart;

	sc = (spnego_gss_ctx_id_t)*ctx;
	ret = GSS_S_DEFECTIVE_TOKEN;
	*negState = REJECT;
	*minstat = 0;
	supportedMech = GSS_C_NO_OID;
	*return_token = ERROR_TOKEN_SEND;
	*responseToken = *mechListMIC = GSS_C_NO_BUFFER;

	ptr = bufstart = buf->value;
#define REMAIN (buf->length - (ptr - bufstart))
	if (REMAIN > INT_MAX)
		return GSS_S_DEFECTIVE_TOKEN;

	/*
	 * Attempt to work with old Sun SPNEGO.
	 */
	if (*ptr == HEADER_ID) {
		ret = g_verify_token_header(gss_mech_spnego,
					    &len, &ptr, 0, REMAIN);
		if (ret) {
			*minstat = ret;
			return GSS_S_DEFECTIVE_TOKEN;
		}
	}
	if (*ptr != (CONTEXT | 0x01)) {
		return GSS_S_DEFECTIVE_TOKEN;
	}
	ret = get_negTokenResp(minstat, ptr, REMAIN,
			       negState, &supportedMech,
			       responseToken, mechListMIC);
	if (ret != GSS_S_COMPLETE)
		goto cleanup;

	if (*responseToken == GSS_C_NO_BUFFER &&
	    *mechListMIC == GSS_C_NO_BUFFER) {

		ret = GSS_S_DEFECTIVE_TOKEN;
		goto cleanup;
	}
	if (supportedMech != GSS_C_NO_OID) {
		ret = GSS_S_DEFECTIVE_TOKEN;
		goto cleanup;
	}
	sc->firstpass = 0;
	*negState = ACCEPT_INCOMPLETE;
	*return_token = CONT_TOKEN_SEND;
cleanup:
	if (supportedMech != GSS_C_NO_OID) {
		generic_gss_release_oid(&tmpmin, &supportedMech);
	}
	return ret;
#undef REMAIN
}
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.