Re: /proc/sys/vm/drop_caches: add error handling

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> 
> Document that drop_caches is unsafe, and add error checking so that it
> bails out on invalid inputs. [Note that this was triggered by Android
> trying to use it in production, and incidentally writing invalid
> value...]

Yup. good patch.

> -	return 0;
> +	int res;
> +	res = proc_dointvec_minmax(table, write, file, buffer, length, ppos);
> +	if (res)
> +		return res;
> +	if (!write)
> +		return res;
> +	if (sysctl_drop_caches & ~3)
> +		return -EINVAL;
> +	if (sysctl_drop_caches & 1)
> +		drop_pagecache();
> +	if (sysctl_drop_caches & 2)
> +		drop_slab();
> +	return res;
>  }

I think following is clarify more.

	res = proc_dointvec_minmax(table, write, file, buffer, length, ppos);
	if (res)
		return res;
	if (!write)
		return 0;
	if (sysctl_drop_caches & ~3)
		return -EINVAL;
	if (sysctl_drop_caches & 1)
		drop_pagecache();
	if (sysctl_drop_caches & 2)
		drop_slab();
	return 0;


otherthings, _very_ looks good to me. :)



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