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

Ben Hutchings
2017-06-29T18:24:43Z

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.