Subject: bug#17455: [PATCH] shred: fix overflow checking of command-line options

From: Jim Meyering <[email-masked]>
Date: Sat, 10 May 2014 12:39:44 -0700

On Sat, May 10, 2014 at 11:42 AM, Paul Eggert <[email-masked]> wrote:
> * src/shred.c (main): Limit -n (number of passes) value to
> ULONG_MAX, not to UINT32_MAX, since the vars are unsigned long.
> Limit the -s (file size) value to OFF_T_MAX.
> ---
>  src/shred.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/src/shred.c b/src/shred.c
> index 607c6be..f4347e0 100644
> --- a/src/shred.c
> +++ b/src/shred.c
...
> @@ -1256,9 +1256,10 @@ main (int argc, char **argv)
>
>          case 's':
>            {
> -            uintmax_t tmp;
> -            if (xstrtoumax (optarg, NULL, 0, &tmp, "cbBkKMGTPEZY0")
> -                != LONGINT_OK)
> +            intmax_t tmp;
> +            if ((xstrtoimax (optarg, NULL, 0, &tmp, "cbBkKMGTPEZY0")
> +                 != LONGINT_OK)
> +                || OFF_T_MAX < tmp)

Hi Paul,
The above makes it so shred now accepts a negative size.
Before, that would be diagnosed as invalid:

   $ shred -s-1 k
   shred: -1: invalid file size

With a size of -2, shred will write 64KB blocks forever -- or until it
runs out of space.

Here's a patch to fix that and to add a test covering that case: