linux-kernel - Re: [PATCH v4 2/6] string_helpers: add kstrdup_quotable

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Date:	Tue, 12 Apr 2016 16:19:42 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	James Morris <jmorris@...ei.org>, Joe Perches <joe@...ches.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Jonathan Corbet <corbet@....net>,
	Kalle Valo <kvalo@...eaurora.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Jiri Slaby <jslaby@...e.com>, Paul Moore <pmoore@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	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, linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 2/6] string_helpers: add kstrdup_quotable_cmdline

Quoting Kees Cook (keescook@...omium.org):
> Provide an escaped (but readable: no inter-argument NULLs) commandline
> safe for logging.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Acked-by: Serge Hallyn <serge.hallyn@...onical.com>

> ---
>  include/linux/string_helpers.h |  1 +
>  lib/string_helpers.c           | 34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
> index 9de228af00c1..684d2695fc36 100644
> --- a/include/linux/string_helpers.h
> +++ b/include/linux/string_helpers.h
> @@ -69,5 +69,6 @@ static inline int string_escape_str_any_np(const char *src, char *dst,
>  }
>  
>  char *kstrdup_quotable(const char *src, gfp_t gfp);
> +char *kstrdup_quotable_cmdline(struct task_struct *task, gfp_t gfp);
>  
>  #endif
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index aa00c9f989ee..b16ee85aaf87 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -10,6 +10,7 @@
>  #include <linux/export.h>
>  #include <linux/ctype.h>
>  #include <linux/errno.h>
> +#include <linux/mm.h>
>  #include <linux/slab.h>
>  #include <linux/string.h>
>  #include <linux/string_helpers.h>
> @@ -562,3 +563,36 @@ char *kstrdup_quotable(const char *src, gfp_t gfp)
>  	return dst;
>  }
>  EXPORT_SYMBOL_GPL(kstrdup_quotable);
> +
> +/*
> + * 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, gfp_t gfp)
> +{
> +	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, leave res pointing to last non-NULL. */
> +	while (--res >= 0 && buffer[res] == '\0')
> +		;
> +
> +	/* 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, gfp);
> +	kfree(buffer);
> +	return quoted;
> +}
> +EXPORT_SYMBOL_GPL(kstrdup_quotable_cmdline);
> -- 
> 2.6.3