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Date: Tue, 16 Mar 2021 11:49:20 -0700
From: Kees Cook <>
To: Linus Torvalds <>
Cc: Alexey Gladkov <>,
	LKML <>,
	io-uring <>,
	Kernel Hardening <>,
	Linux Containers <>,
	Linux-MM <>, Alexey Gladkov <>,
	Andrew Morton <>,
	Christian Brauner <>,
	"Eric W . Biederman" <>,
	Jann Horn <>, Jens Axboe <>,
	Oleg Nesterov <>
Subject: Re: [PATCH v8 3/8] Use atomic_t for ucounts reference counting

On Mon, Mar 15, 2021 at 03:19:17PM -0700, Linus Torvalds wrote:
> It just saturates, and doesn't have the "don't do this" case, which
> the ucounts case *DOES* have.

Right -- I saw that when digging through the thread. I'm honestly
curious, though, why did the 0-day bot find a boot crash? (I can't
imagine ucounts wrapped in 0.4 seconds.) So it looked like an
increment-from-zero case, which seems like it would be a bug?

> I know you are attached to refcounts, but really: they are not only

Heh, right -- I'm not arguing that refcount_t MUST be used, I just didn't
see the code path that made them unsuitable: hitting INT_MAX - 128 seems
very hard to do. Anyway, I'll go study it more to try to understand what
I'm missing.

Kees Cook

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