linux-kernel - Re: [PATCH 6/9] x86/intel_rdt: Add support for cache bit mask management

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Message-ID: <20150728163742.GT25159@twins.programming.kicks-ass.net>
Date:	Tue, 28 Jul 2015 18:37:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, vikas.shivappa@...el.com,
	x86@...nel.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...nel.org, tj@...nel.org, matt.fleming@...el.com,
	will.auld@...el.com, glenn.p.williamson@...el.com,
	kanaka.d.juvva@...el.com
Subject: Re: [PATCH 6/9] x86/intel_rdt: Add support for cache bit mask
 management

On Wed, Jul 01, 2015 at 03:21:07PM -0700, Vikas Shivappa wrote:
> +static int cbm_validate(struct intel_rdt *ir, unsigned long cbmvalue)
> +{
> +	struct cgroup_subsys_state *css;
> +	struct intel_rdt *par, *c;
> +	unsigned long *cbm_tmp;
> +	int err = 0;
> +
> +	if (!cbm_is_contiguous(cbmvalue)) {
> +		pr_err("bitmask should have >= 1 bit and be contiguous\n");
> +		err = -EINVAL;
> +		goto out_err;
> +	}

> +static struct cftype rdt_files[] = {
> +	{
> +		.name		= "l3_cache_mask",
> +		.seq_show	= intel_cache_alloc_cbm_read,
> +		.write_u64	= intel_cache_alloc_cbm_write,
> +		.mode		= 0666,

So this file is world writable? How is the above pr_err() not a DoS ?

> +	},
> +	{ }	/* terminate */
> +};
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