linux-kernel - RE: [PATCH 0/1] Slightly relax the type checking done by min() and max().

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Message-ID: <7e594ad64e444d448c747688b8f28249@AcuMS.aculab.com>
Date:   Fri, 25 Nov 2022 15:27:07 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "'Joe Perches'" <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: RE: [PATCH 0/1] Slightly relax the type checking done by min() and
 max().

From: Andy Shevchenko
> Sent: 25 November 2022 15:21
> 
> On Fri, Nov 25, 2022 at 03:00:40PM +0000, David Laight wrote:
> > The min() and max() defines include a type check to avoid the unexpected
> >   behaviour when a negative value is compared against and unsigned value.
> > However a lot of code hits this check and uses min_t() to avoid the error.
> > Many of these are just plain wrong.
> >
> > Those casting to u8 or u16 are particularly suspect, eg:
> > drivers/usb/misc/usb251xb.c:528:
> > 		hub->max_current_sp = min_t(u8, property_u32 / 2000, 50);
> 
> I don't buy this. What's exactly wrong with this code?

Consider what happens if propery_u32 is 512000.
The returned value is 0 not 50.

	David

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