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

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Message-ID: <87h9l8skoe.fsf@vitty.brq.redhat.com>
Date:	Fri, 30 Oct 2015 11:41:21 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	James Bottomley <jbottomley@...n.com>
Cc:	"andy.shevchenko\@gmail.com" <andy.shevchenko@...il.com>,
	"ulf.hansson\@linaro.org" <ulf.hansson@...aro.org>,
	"linux\@rasmusvillemoes.dk" <linux@...musvillemoes.dk>,
	"andriy.shevchenko\@linux.intel.com" 
	<andriy.shevchenko@...ux.intel.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm\@linux-foundation.org" <akpm@...ux-foundation.org>,
	"keescook\@chromium.org" <keescook@...omium.org>
Subject: Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

James Bottomley <jbottomley@...n.com> writes:

> On Fri, 2015-10-30 at 01:32 +0200, Andy Shevchenko wrote:
>> On Fri, Oct 30, 2015 at 1:00 AM, James Bottomley <jbottomley@...n.com> wrote:
>> > 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.
>> 
>> For *block* size? It will crash the kernel. I've checked, it wasn't
>> changed from the beginning (b9f28d863594).
>
> The standard signal for a drive error in capacity is zero size and zero
> block size.  We have to take that case as standard without emitting
> scary warnings.

Ok, but what if size != 0? Is WARN_ON() justified in this case?

-- 
  Vitaly
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