linux-kernel - Re: [RFC/RFT PATCH 5/6] random: Plug race in preceding patch

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Message-ID: <CAMj1kXFnfjGXwNZDSE1yhXhXyNdMP7DWa9es4VoHStF-g7pC7g@mail.gmail.com>
Date: Fri, 28 Nov 2025 12:18:38 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: david laight <david.laight@...box.com>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-hardening@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Kees Cook <kees@...nel.org>, Ryan Roberts <ryan.roberts@....com>, Will Deacon <will@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Jeremy Linton <jeremy.linton@....com>, 
	Catalin Marinas <Catalin.Marinas@....com>, Mark Rutland <mark.rutland@....com>, 
	"Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [RFC/RFT PATCH 5/6] random: Plug race in preceding patch

On Fri, 28 Nov 2025 at 12:13, david laight <david.laight@...box.com> wrote:
>
> On Thu, 27 Nov 2025 10:22:32 +0100
> Ard Biesheuvel <ardb+git@...gle.com> wrote:
>
> > From: Ard Biesheuvel <ardb@...nel.org>
> >
> > The lockless get_random_uXX() reads the next value from the linear
> > buffer and then overwrites it with a 0x0 value. This is racy, as the
> > code might be re-entered by an interrupt handler, and so the store might
> > redundantly wipe the location accessed by the interrupt context rather
> > than the interrupted context.
>
> Is overwriting the used value even useful?

That is an interesting question but it is orthogonal to this series.