Re: Fw: [PATCH] lib/kstrtox.c Stop parsing integer on overflow

[Alexey Dobriyan]

On Tue, Feb 17, 2015 at 04:17:24PM -0800, Andrew Morton wrote:
> ?
> 
> Begin forwarded message:
> 
> Date: Mon, 16 Feb 2015 10:48:50 -0800
> From: Anshul Garg <aksgarg1989@xxxxxxxxx>
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: aksgarg1989@xxxxxxxxx, anshul.g@xxxxxxxxxxx, torvalds@xxxxxxxxxxxxxxxxxxxx
> Subject: [PATCH] lib/kstrtox.c Stop parsing integer on overflow
> 
> 
> From: Anshul Garg <aksgarg1989@xxxxxxxxx>
> 
> While converting string representation to integer
> break the loop if overflow is detected.
> 
> Signed-off-by: Anshul Garg <aksgarg1989@xxxxxxxxx>
> ---
>  lib/kstrtox.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/kstrtox.c b/lib/kstrtox.c
> index ec8da78..6f30209 100644
> --- a/lib/kstrtox.c
> +++ b/lib/kstrtox.c
> @@ -70,8 +70,10 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
>  		 * it in the max base we support (16)
>  		 */
>  		if (unlikely(res & (~0ull << 60))) {
> -			if (res > div_u64(ULLONG_MAX - val, base))
> +			if (res > div_u64(ULLONG_MAX - val, base)) {
>  				overflow = 1;
> +				break;
> +			}
>  		}
>  		res = res * base + val;
>  		rv++;

The _notion_ of a patch is OK if you want EVERY simple_strtoull() call
to stop parsing past overflow right now. It SHOULD have done so from day 1,
but it doesn't do that.

When I wrote kstrto*() code I deliberatedly didn't break this bug
because of the sheer number of call sites.

If you are OK with changing bug-for-bug compatibility,
then patch simply need to delete overflow detection code.

	Alexey
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