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Date:   Mon, 18 Jan 2021 20:45:51 +0100
From:   Alexey Gladkov <gladkov.alexey@gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     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>,
        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>,
        Kees Cook <keescook@chromium.org>,
        Oleg Nesterov <oleg@redhat.com>
Subject: Re: [RFC PATCH v3 1/8] Use refcount_t for ucounts reference counting
Message-ID: <20210118194551.h2hrwof7b3q5vgoi@example.org>
References: <cover.1610722473.git.gladkov.alexey@gmail.com>
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 <CAHk-=wjsg0Lgf1Mh2UiJE4sqBDDo0VhFVBUbhed47ot2CQQwfQ@mail.gmail.com>
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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@gmail.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