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From: Kees Cook <keescook@chromium.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Linux Containers <containers@lists.linux-foundation.org>,
	Jann Horn <jannh@google.com>, LKML <linux-kernel@vger.kernel.org>,
	Oleg Nesterov <oleg@redhat.com>, Linux-MM <linux-mm@kvack.org>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexey Gladkov <legion@kernel.org>,
	io-uring <io-uring@vger.kernel.org>
Subject: Re: [PATCH v8 3/8] Use atomic_t for ucounts reference counting
Date: Tue, 16 Mar 2021 11:49:20 -0700	[thread overview]
Message-ID: <202103161146.E118DE5@keescook> (raw)
In-Reply-To: <CAHk-=wjYOCgM+mKzwTZwkDDg12DdYjFFkmoFKYLim7NFmR9HBg@mail.gmail.com>

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
> more expensive, THEY LITERALLY DO THE WRONG THING.

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
_______________________________________________
Containers mailing list
Containers@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/containers

WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexey Gladkov <gladkov.alexey@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	io-uring <io-uring@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Linux Containers <containers@lists.linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>, Alexey Gladkov <legion@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Jann Horn <jannh@google.com>, Jens Axboe <axboe@kernel.dk>,
	Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH v8 3/8] Use atomic_t for ucounts reference counting
Date: Tue, 16 Mar 2021 11:49:20 -0700	[thread overview]
Message-ID: <202103161146.E118DE5@keescook> (raw)
In-Reply-To: <CAHk-=wjYOCgM+mKzwTZwkDDg12DdYjFFkmoFKYLim7NFmR9HBg@mail.gmail.com>

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
> more expensive, THEY LITERALLY DO THE WRONG THING.

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

  reply	other threads:[~2021-03-16 18:49 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-10 12:01 [PATCH v8 0/8] Count rlimits in each user namespace Alexey Gladkov
2021-03-10 12:01 ` Alexey Gladkov
2021-03-10 12:01 ` [PATCH v8 1/8] Increase size of ucounts to atomic_long_t Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov
2021-03-10 12:01 ` [PATCH v8 2/8] Add a reference to ucounts for each cred Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov
2021-03-10 12:01 ` [PATCH v8 3/8] Use atomic_t for ucounts reference counting Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov
2021-03-10 21:14   ` Linus Torvalds
2021-03-10 21:14     ` Linus Torvalds
2021-03-15 22:02   ` Kees Cook
2021-03-15 22:02     ` Kees Cook
2021-03-15 22:19     ` Linus Torvalds
2021-03-15 22:19       ` Linus Torvalds
2021-03-16 18:49       ` Kees Cook [this message]
2021-03-16 18:49         ` Kees Cook
2021-03-16 19:26         ` Linus Torvalds
2021-03-16 19:26           ` Linus Torvalds
2021-03-16 19:32           ` Kees Cook
2021-03-16 19:32             ` Kees Cook
2021-03-10 12:01 ` [PATCH v8 4/8] Reimplement RLIMIT_NPROC on top of ucounts Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov
2021-03-10 12:01 ` [PATCH v8 5/8] Reimplement RLIMIT_MSGQUEUE " Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov
2021-03-10 12:01 ` [PATCH v8 6/8] Reimplement RLIMIT_SIGPENDING " Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov
2021-03-10 12:01 ` [PATCH v8 7/8] Reimplement RLIMIT_MEMLOCK " Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov
2021-03-10 12:01 ` [PATCH v8 8/8] kselftests: Add test to check for rlimit changes in different user namespaces Alexey Gladkov
2021-03-10 12:01   ` Alexey Gladkov

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