linux-kernel - RE: [PATCH next v3 0/5] minmax: Relax type checks in min() and max().

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Message-ID: <bcf2fcad28c048058c808ec9e749da80@AcuMS.aculab.com>
Date:   Thu, 24 Aug 2023 09:05:28 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>
CC:     Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: RE: [PATCH next v3 0/5] minmax: Relax type checks in min() and max().

From: Linus Torvalds
> Sent: Wednesday, August 23, 2023 4:32 PM
...
> That might get rid of a number of the more annoying cases.

The one it leaves is code like:

	int length = get_length(...);
	if (length <= 0)
		return error:
	do {
		frag_len = some_min_function(length, PAGE_SIZE);
		...
	} while ((length -= frag_len) != 0);

As written it is ok for all reasonable some_min_function().

But if the (length <= 0) test is missing it really doesn't
matter what some_min_function() returns because the code
isn't going to do anything sensible - and may just loop.

About the only thing you could do is add a run-time check
and then BUG() if negative.
But that is horrid...

	David

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