Message-ID: <1498760667.1935.69.camel@codethink.co.uk>
Subject: Re: [PATCH 4.4 03/26] lib/cmdline.c: fix get_options() overflow
 while parsing ranges
From: Ben Hutchings <ben.hutchings@codethink.co.uk>
To: "Ilya V. Matveychikov" <matvejchikov@gmail.com>
Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Thu, 29 Jun 2017 19:24:27 +0100
In-Reply-To: <20170627124529.091915723@linuxfoundation.org>
References: <20170627124528.581163327@linuxfoundation.org>
         <20170627124529.091915723@linuxfoundation.org>
Organization: Codethink Ltd.
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On Tue, 2017-06-27 at 14:49 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Ilya Matveychikov <matvejchikov@gmail.com>
> 
> commit a91e0f680bcd9e10c253ae8b62462a38bd48f09f upstream.
> 
> When using get_options() it's possible to specify a range of numbers,
> like 1-100500.  The problem is that it doesn't track array size while
> calling internally to get_range() which iterates over the range and
> fills the memory with numbers.
[...]
> --- a/lib/cmdline.c
> +++ b/lib/cmdline.c
> @@ -22,14 +22,14 @@
>   *	the values[M, M+1, ..., N] into the ints array in get_options.
>   */
>  
> -static int get_range(char **str, int *pint)
> +static int get_range(char **str, int *pint, int n)
>  {
>  	int x, inc_counter, upper_range;
>  
>  	(*str)++;
>  	upper_range = simple_strtol((*str), NULL, 0);
>  	inc_counter = upper_range - *pint;
> -	for (x = *pint; x < upper_range; x++)
> +	for (x = *pint; n && x < upper_range; x++, n--)
>  		*pint++ = x;
>  	return inc_counter;
>  }

But this still returns the number of integers in the range (minus 1)...

> @@ -96,7 +96,7 @@ char *get_options(const char *str, int n
>  			break;
>  		if (res == 3) {
>  			int range_nums;
> -			range_nums = get_range((char **)&str, ints + i);
> +			range_nums = get_range((char **)&str, ints + i, nints - i);
>  			if (range_nums < 0)
>  				break;
>  			/*

...so that get_options() may set i > nints and ints[0] > nints - 1.
That will presumably result in out-of-bounds reads in callers.

(This set of functions really deserves to be given a test suite and then
rewritten, because they are a *mess*.)

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.