linux-kernel - Re: [PATCH][next] media: atomisp: Fix incorrect snprintf format specifiers for signed integers

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Message-ID: <934c7ffa-1386-45a0-a4e7-f2b93cca6370@suswa.mountain>
Date: Sat, 2 Aug 2025 12:02:35 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Colin Ian King <colin.i.king@...il.com>,
	Andy Shevchenko <andy@...nel.org>, Hans de Goede <hansg@...nel.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] media: atomisp: Fix incorrect snprintf format
 specifiers for signed integers

On Sat, Aug 02, 2025 at 10:45:49AM +0200, Andy Shevchenko wrote:
> On Sat, Aug 2, 2025 at 9:32 AM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > On Fri, Aug 01, 2025 at 11:57:43PM +0200, Andy Shevchenko wrote:
> > > On Fri, Aug 1, 2025 at 6:01 PM Colin Ian King <colin.i.king@...il.com> wrote:
> > > >
> > > > There are incorrect %u format specifiers being used to for signed integers,
> > > > fix this by using %d instead.
> > >
> > > Both of them sound to me like the fix of the symptom and not the
> > > cause. Can we simply make types of the iterators to be unsigned
> > > instead?
> >
> > Making iterator unsigned by default only increases the rate of bugs.
> 
> How? Please, make sure this is relevant to this case.

You're suggesting that he should change:

-	int i, j;
+	unsigned int i, j;

It's just bad advice.  Making iterators unsigned makes the code less
safe.  It leads underflow bugs when we do subtraction:

	for (i = num - 1; i < limit; i++) {

Now i starts at UINT_MAX.  Which I guess is fine in this example...

But it also leads to endless loops in the error handling:

	while (i-- >= 0) {

Making iterators unsigned is a bad habbit and it's bad advice in terms
of the data that we have with regards to bugs.

regards,
dan carpenter