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Date: Mon, 18 Jan 2021 20:45:51 +0100
From: Alexey Gladkov <gladkov.alexey@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
io-uring <io-uring@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux Containers <containers@...ts.linux-foundation.org>,
Linux-MM <linux-mm@...ck.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Christian Brauner <christian.brauner@...ntu.com>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
Kees Cook <keescook@...omium.org>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC PATCH v3 1/8] Use refcount_t for ucounts reference counting
On Mon, Jan 18, 2021 at 11:14:48AM -0800, Linus Torvalds wrote:
> On Fri, Jan 15, 2021 at 6:59 AM Alexey Gladkov <gladkov.alexey@...il.com> wrote:
> >
> > @@ -152,10 +153,7 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
> > ucounts = new;
> > }
> > }
> > - if (ucounts->count == INT_MAX)
> > - ucounts = NULL;
> > - else
> > - ucounts->count += 1;
> > + refcount_inc(&ucounts->count);
> > spin_unlock_irq(&ucounts_lock);
> > return ucounts;
> > }
>
> This is wrong.
>
> It used to return NULL when the count saturated.
>
> Now it just silently saturates.
>
> I'm not sure how many people care, but that NULL return ends up being
> returned quite widely (through "inc_uncount()" and friends).
>
> The fact that this has no commit message at all to explain what it is
> doing and why is also a grounds for just NAK.
Sorry about that. I thought that this code is not needed when switching
from int to refcount_t. I was wrong. I'll think about how best to check
it.
--
Rgrds, legion
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