From: Kees Cook <keescook@chromium.org>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Alexey Gladkov <gladkov.alexey@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux Containers <containers@lists.linux-foundation.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Alexey Gladkov <legion@kernel.org>,
Christian Brauner <christian@brauner.io>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC PATCH v2 1/8] Use atomic type for ucounts reference counting
Date: Wed, 13 Jan 2021 10:01:55 -0800 [thread overview]
Message-ID: <202101131001.BF1108F90@keescook> (raw)
In-Reply-To: <878s8wdcib.fsf@x220.int.ebiederm.org>
On Wed, Jan 13, 2021 at 10:31:40AM -0600, Eric W. Biederman wrote:
> Alexey Gladkov <gladkov.alexey@gmail.com> writes:
>
> We might want to use refcount_t instead of atomic_t. Not a big deal
> either way.
Yes, please use refcount_t, and don't use _read() since that introduces
races.
-Kees
>
> > Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
> > ---
> > include/linux/user_namespace.h | 2 +-
> > kernel/ucount.c | 10 +++++-----
> > 2 files changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> > index 64cf8ebdc4ec..84fefa9247c4 100644
> > --- a/include/linux/user_namespace.h
> > +++ b/include/linux/user_namespace.h
> > @@ -92,7 +92,7 @@ struct ucounts {
> > struct hlist_node node;
> > struct user_namespace *ns;
> > kuid_t uid;
> > - int count;
> > + atomic_t count;
> > atomic_t ucount[UCOUNT_COUNTS];
> > };
> >
> > diff --git a/kernel/ucount.c b/kernel/ucount.c
> > index 11b1596e2542..0f2c7c11df19 100644
> > --- a/kernel/ucount.c
> > +++ b/kernel/ucount.c
> > @@ -141,7 +141,8 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
> >
> > new->ns = ns;
> > new->uid = uid;
> > - new->count = 0;
> > +
> > + atomic_set(&new->count, 0);
> >
> > spin_lock_irq(&ucounts_lock);
> > ucounts = find_ucounts(ns, uid, hashent);
> > @@ -152,10 +153,10 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
> > ucounts = new;
> > }
> > }
> > - if (ucounts->count == INT_MAX)
> > + if (atomic_read(&ucounts->count) == INT_MAX)
> > ucounts = NULL;
> > else
> > - ucounts->count += 1;
> > + atomic_inc(&ucounts->count);
> > spin_unlock_irq(&ucounts_lock);
> > return ucounts;
> > }
> > @@ -165,8 +166,7 @@ static void put_ucounts(struct ucounts *ucounts)
> > unsigned long flags;
> >
> > spin_lock_irqsave(&ucounts_lock, flags);
> > - ucounts->count -= 1;
> > - if (!ucounts->count)
> > + if (atomic_dec_and_test(&ucounts->count))
> > hlist_del_init(&ucounts->node);
> > else
> > ucounts = NULL;
>
>
> This can become:
> static void put_ucounts(struct ucounts *ucounts)
> {
> unsigned long flags;
>
> if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) {
> hlist_del_init(&ucounts->node);
> spin_unlock_irqrestore(&ucounts_lock);
> kfree(ucounts);
> }
> }
>
--
Kees Cook
next prev parent reply other threads:[~2021-01-13 18:02 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-10 17:33 [RFC PATCH v2 0/8] Count rlimits in each user namespace Alexey Gladkov
2021-01-10 17:33 ` [RFC PATCH v2 1/8] Use atomic type for ucounts reference counting Alexey Gladkov
2021-01-13 16:31 ` Eric W. Biederman
2021-01-13 18:01 ` Kees Cook [this message]
2021-01-10 17:33 ` [RFC PATCH v2 2/8] Add a reference to ucounts for each user Alexey Gladkov
2021-01-13 6:33 ` 59ebc79722: kernel_BUG_at_kernel/cred.c kernel test robot
2021-01-13 16:25 ` [RFC PATCH v2 2/8] Add a reference to ucounts for each user Eric W. Biederman
2021-01-10 17:33 ` [RFC PATCH v2 3/8] Increase size of ucounts to atomic_long_t Alexey Gladkov
2021-01-10 17:33 ` [RFC PATCH v2 4/8] Move RLIMIT_NPROC counter to ucounts Alexey Gladkov
2021-01-10 17:33 ` [RFC PATCH v2 5/8] Move RLIMIT_MSGQUEUE " Alexey Gladkov
2021-01-10 17:33 ` [RFC PATCH v2 6/8] Move RLIMIT_SIGPENDING " Alexey Gladkov
2021-01-10 17:33 ` [RFC PATCH v2 7/8] Move RLIMIT_MEMLOCK " Alexey Gladkov
2021-01-10 17:33 ` [RFC PATCH v2 8/8] Move RLIMIT_NPROC check to the place where we increment the counter Alexey Gladkov
2021-01-10 18:46 ` [RFC PATCH v2 0/8] Count rlimits in each user namespace Linus Torvalds
2021-01-11 20:17 ` Eric W. Biederman
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