From: Kees Cook <keescook@chromium.org>
To: Shuah Khan <skhan@linuxfoundation.org>
Cc: corbet@lwn.net, gregkh@linuxfoundation.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 01/11] counters: Introduce counter_atomic* counters
Date: Fri, 9 Oct 2020 11:00:54 -0700 [thread overview]
Message-ID: <202010091100.9327D918@keescook> (raw)
In-Reply-To: <baede266cc0c69da61142b467ff386c6b31a70b7.1602209970.git.skhan@linuxfoundation.org>
On Fri, Oct 09, 2020 at 09:55:56AM -0600, Shuah Khan wrote:
> Introduce Simple atomic counters.
>
> There are a number of atomic_t usages in the kernel where atomic_t api
> is used strictly for counting and not for managing object lifetime. In
> some cases, atomic_t might not even be needed.
>
> The purpose of these counters is to clearly differentiate atomic_t
> counters from atomic_t usages that guard object lifetimes, hence prone
> to overflow and underflow errors. It allows tools that scan for underflow
> and overflow on atomic_t usages to detect overflow and underflows to scan
> just the cases that are prone to errors.
>
> Simple atomic counters api provides interfaces for simple atomic counters
> that just count, and don't guard resource lifetimes. The interfaces are
> built on top of atomic_t api, providing a smaller subset of atomic_t
> interfaces necessary to support simple counters.
>
> Counter wraps around to INT_MIN when it overflows and should not be used
> to guard resource lifetimes, device usage and open counts that control
> state changes, and pm states. Overflowing to INT_MIN is consistent with
> the atomic_t api, which it is built on top of.
>
> Using counter_atomic* to guard lifetimes could lead to use-after free
> when it overflows and undefined behavior when used to manage state
> changes and device usage/open states.
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
next prev parent reply other threads:[~2020-10-09 18:00 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-09 15:55 [PATCH v3 00/11] Introduce Simple atomic counters Shuah Khan
2020-10-09 15:55 ` [PATCH v3 01/11] counters: Introduce counter_atomic* counters Shuah Khan
2020-10-09 18:00 ` Kees Cook [this message]
2020-10-09 19:49 ` Peter Zijlstra
2020-10-13 11:27 ` Mauro Carvalho Chehab
2020-10-15 1:11 ` Shuah Khan
2020-10-09 18:03 ` [PATCH v3 00/11] Introduce Simple atomic counters Kees Cook
2020-10-09 19:02 ` Shuah Khan
2020-10-09 19:37 ` Peter Zijlstra
2020-10-09 20:45 ` Kees Cook
2020-10-10 11:09 ` Peter Zijlstra
2020-10-14 2:12 ` Shuah Khan
2020-10-14 9:17 ` Peter Zijlstra
2020-10-14 23:31 ` Kees Cook
2020-10-16 10:53 ` Peter Zijlstra
2020-10-16 22:51 ` Kees Cook
2020-11-10 18:49 ` Dan Carpenter
2020-10-16 21:56 ` Shuah Khan
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