linux-kernel - Re: [PATCH v2 2/5] string_helpers: add kstrdup_quotable

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Date:	Wed, 30 Mar 2016 14:07:19 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Kees Cook <keescook@...omium.org>, James Morris <jmorris@...ei.org>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kalle Valo <kvalo@...eaurora.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Joe Perches <joe@...ches.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Jiri Slaby <jslaby@...e.com>, Paul Moore <pmoore@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Andreas Gruenbacher <agruenba@...hat.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] string_helpers: add kstrdup_quotable_cmdline

On Mon, 2016-03-28 at 14:14 -0700, Kees Cook wrote:
> Provide an escaped (but readable: no inter-argument NULLs)
> commandline
> safe for logging.

> +/*
> + * Returns allocated NULL-terminated string containing process
> + * command line, with inter-argument NULLs replaced with spaces,
> + * and other special characters escaped.
> + */
> +char *kstrdup_quotable_cmdline(struct task_struct *task)
> +{
> +	char *buffer, *quoted;
> +	int i, res;
> +
> +	buffer = kmalloc(PAGE_SIZE, GFP_TEMPORARY);
> +	if (!buffer)
> +		return NULL;
> +
> +	res = get_cmdline(task, buffer, PAGE_SIZE - 1);
> +	buffer[res] = '\0';
> +
> +	/* Collapse trailing NULLs. */
> +	for (; res > 0; res--)
> +		if (buffer[res-1] != '\0')
> +			break;

/* buffer[res] is '\0', so, predecrement is safe here */
while (buffer[--res] == '\0')
 /* nothing */;

?

> +
> +	/* Replace inter-argument NULLs. */
> +	for (i = 0; i < res; i++)
> +		if (buffer[i] == '\0')
> +			buffer[i] = ' ';
> +
> +	/* Make sure result is printable. */
> +	quoted = kstrdup_quotable(buffer);
> +	kfree(buffer);
> +	return quoted;
> +}
> +EXPORT_SYMBOL_GPL(kstrdup_quotable_cmdline);

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy