linux-kernel - Re: [RFC PATCH v3 1/8] Use refcount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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