[PATCH 01/11] params: bound array element output to the caller's page buffer

[Andy Shevchenko]

On Thu, May 21, 2026 at 06:33:14AM -0700, Kees Cook wrote:
> 
> param_array_get() appends each element's string representation into the
> shared sysfs page buffer by passing buffer + off to the element getter.
> 
> That works for getters that only write a small bounded string, but
> param_get_charp() and similar helpers format against PAGE_SIZE from the
> pointer they receive. Once off is non-zero, an element getter can
> therefore write past the end of the original sysfs page buffer.
> 
> Collect each element into a temporary PAGE_SIZE buffer first and then
> copy only the remaining space into the caller's page buffer.

...

> +	elem_buf = kmalloc(PAGE_SIZE, GFP_KERNEL);

get_free_page() (or how it is called)?

> +	if (!elem_buf)
> +		return -ENOMEM;
> +
>  	for (i = off = 0; i < (arr->num ? *arr->num : arr->max); i++) {
> -		/* Replace \n with comma */
> -		if (i)
> -			buffer[off - 1] = ',';
>  		p.arg = arr->elem + arr->elemsize * i;
>  		check_kparam_locked(p.mod);
> -		ret = arr->ops->get(buffer + off, &p);
> +		ret = arr->ops->get(elem_buf, &p);
>  		if (ret < 0)
> -			return ret;
> +			goto out;
> +		ret = min(ret, (int)(PAGE_SIZE - 1 - off));

It's usually discouraged to use castings in min/max/clamp. Can we make ret long
or do something different here?

> +		if (!ret)
> +			break;

> +		/* Replace the previous element's trailing newline with a comma. */
> +		if (i)
> +			buffer[off - 1] = ',';

Can't we do this after with help of strreplace()?

> +		memcpy(buffer + off, elem_buf, ret);
>  		off += ret;
> +		if (off == PAGE_SIZE - 1)
> +			break;
>  	}
>  	buffer[off] = '\0';
> -	return off;
> +	ret = off;
> +out:
> +	kfree(elem_buf);
> +	return ret;

-- 
With Best Regards,
Andy Shevchenko