linux-kernel - Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk

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Date:	Thu, 29 Oct 2015 23:00:39 +0000
From:	James Bottomley <jbottomley@...n.com>
To:	"vkuznets@...hat.com" <vkuznets@...hat.com>
CC:	"ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
	"linux@...musvillemoes.dk" <linux@...musvillemoes.dk>,
	"andriy.shevchenko@...ux.intel.com" 
	<andriy.shevchenko@...ux.intel.com>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size()
 against blk_size=0

On Thu, 2015-10-29 at 17:30 +0100, Vitaly Kuznetsov wrote:
> Division by zero happens if blk_size=0 is supplied to string_get_size().
> Add WARN_ON() and set size to 0 to report '0 B'.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  lib/string_helpers.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index f6c27dc..ff3575b 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -50,6 +50,11 @@ void string_get_size(u64 size, u32 blk_size, const enum string_size_units units,
>  
>  	tmp[0] = '\0';
>  	i = 0;
> +
> +	/* Calling string_get_size() with blk_size=0 is wrong! */
> +	if (WARN_ON(!blk_size))

Get rid of the WARN_ON; it's the standard thing to do for a partially
connected device.  Seeing zero is standard in a whole variety of
situations.  SCSI shims the zero but most other drivers don't.

James