linux-kernel - Re: [PATCH 4.4 03/26] lib/cmdline.c: fix get_options() overflow while parsing ranges

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Date:   Wed, 27 Sep 2017 11:36:21 +0100
From:   Ilya Matveychikov <matvejchikov@...il.com>
To:     Ben Hutchings <ben.hutchings@...ethink.co.uk>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 4.4 03/26] lib/cmdline.c: fix get_options() overflow while
 parsing ranges


> On Jun 29, 2017, at 7:24 PM, Ben Hutchings <ben.hutchings@...ethink.co.uk> wrote:
> 
> 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@...il.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*.)
> 

Please review the approach of fixing that:
https://lkml.org/lkml/2017/9/19/105

> Ben.
> 
> -- 
> Ben Hutchings
> Software Developer, Codethink Ltd.
> 
>