linux-kernel - Re: [PATCH] refcount: Report UAF for refcount_sub_and

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Message-Id: <172123456264.2736908.1565336371503980585.b4-ty@kernel.org>
Date: Wed, 17 Jul 2024 09:42:45 -0700
From: Kees Cook <kees@...nel.org>
To: Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	Petr Pavlu <petr.pavlu@...e.com>
Cc: Kees Cook <kees@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] refcount: Report UAF for refcount_sub_and_test(0) when counter==0

On Wed, 17 Jul 2024 15:00:23 +0200, Petr Pavlu wrote:
> When a reference counter is at zero and refcount_sub_and_test() is invoked
> to subtract zero, the function accepts this request without any warning and
> returns true. This behavior does not seem ideal because the counter being
> already at zero indicates a use-after-free. Furthermore, returning true by
> refcount_sub_and_test() in this case potentially results in a double-free
> done by its caller.
> 
> [...]

(Peter, let me know if you'd rather this went via a different tree...)

Applied to for-linus/hardening, thanks!

[1/1] refcount: Report UAF for refcount_sub_and_test(0) when counter==0
      https://git.kernel.org/kees/c/cee1fb1bb8bd

Take care,

-- 
Kees Cook