Re: [PATCH] lib/string_helpers.c: fix infinite loop in string_get_size()

James Bottomley
2015-09-11T01:22:54Z

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On Fri, 2015-09-04 at 14:56 +0200, Vitaly Kuznetsov wrote:
> string_get_size(1, 512, 0, ..., ...) call results in an infinite loop. The
> problem is that if size == 0 when we start calculating sf_cap this loop
> will never end.
>
> The caller causing the issue is sd_read_capacity(), the problem was noticed
> on Hyper-V.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> lib/string_helpers.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index c98ae81..a155c7b 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -76,7 +76,7 @@ void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
> i++;
> }
>
> - sf_cap = size;
> + sf_cap = size ? size : 1;

If size can become zero after the scale adjustment, then there's a fault
in the algorithm, and this probably isn't the right fix. However, I did
a brief calculation, and I can't see how size becomes zero ... it might
be that I haven't looked at this long enough (I am on holiday).

James

> for (j = 0; sf_cap*10 < 1000; j++)
> sf_cap *= 10;
>

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