linux-kernel - Re: [PATCH] lib/string_helpers.c: fix infinite loop in string_get

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Date:	Fri, 11 Sep 2015 18:31:07 +0000
From:	James Bottomley <jbottomley@...n.com>
To:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:	"linux@...musvillemoes.dk" <linux@...musvillemoes.dk>,
	"andriy.shevchenko@...ux.intel.com" 
	<andriy.shevchenko@...ux.intel.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kys@...rosoft.com" <kys@...rosoft.com>
Subject: Re: [PATCH] lib/string_helpers.c: fix infinite loop in
 string_get_size()

On Thu, 2015-09-10 at 16:08 -0700, Andrew Morton wrote:
> On Fri,  4 Sep 2015 14:56:33 +0200 Vitaly Kuznetsov <vkuznets@...hat.com> 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.
> 
> When fixing bugs, please provide enough info for others to be able to
> understand which kernel version(s) need the fix.  In this case: what
> end-user action triggers this bug?  (iow, how does sdkp->capacity
> become zero?)

Any more details.  The attached programme, which is cut straight out of
the algorithm in string_helpers.c and modified for a C environment
slightly (only in do_div and the typedefs) produces this

hello
STRING IS 512 B

With your input, so I don't think the problem is where you think it is.

James


View attachment "test.c" of type "text/x-csrc" (2502 bytes)