linux-kernel - Re: [PATCH][next] driver core: platform: fix u32 greater or equal to zero comparison

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Message-ID: <20200117050609.GD19765@kadam>
Date:   Fri, 17 Jan 2020 08:06:09 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Simon Schwartz <kern.simon@...schwartz.xyz>,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] driver core: platform: fix u32 greater or equal to
 zero comparison

On Fri, Jan 17, 2020 at 07:42:16AM +0300, Dan Carpenter wrote:
> On Thu, Jan 16, 2020 at 05:57:58PM +0000, Colin King wrote:
> > From: Colin Ian King <colin.king@...onical.com>
> > 
> > Currently the check that a u32 variable i is >= 0 is always true because
> > the unsigned variable will never be negative, causing the loop to run
> > forever.  Fix this by changing the pre-decrement check to a zero check on
> > i followed by a decrement of i.
> > 
> > Addresses-Coverity: ("Unsigned compared against 0")
> > Fixes: 39cc539f90d0 ("driver core: platform: Prevent resouce overflow from causing infinite loops")
> 

Also by the way say you have:

	unsigned int limit = (unsigned)INT_MAX + 4;
	int i;

	for (i = 0; i < limit; i++)
		;
	printf("%d\n", i);


The loop will work the same way regardless of if int is signed or not
because of type promotion.

regards,
dan carpenter