From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0AC75C433DB for ; Wed, 13 Jan 2021 18:02:18 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 0B0E521534 for ; Wed, 13 Jan 2021 18:02:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0B0E521534 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-20640-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 11582 invoked by uid 550); 13 Jan 2021 18:02:10 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 11550 invoked from network); 13 Jan 2021 18:02:09 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=2yOASqLXCFmH8rHiDFY5aK5IF9dZ2OI5aQ21Vbh1eP8=; b=gHtUHzUPG5nr4qeM6RqXwHoa31eiMAo2G3XbBdMPhPetpWhM+8FxJcVQrQckAjJOts a+PuAK+iIngRm+Yp1MRDCVK0BKRkRO9ogHvQh8O/VHesI2z8n5+VeisZVKsjgEqjLV5k U3cHR0de4KgfDQBMl4Uj4g9/NyiGrIcwhViN8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=2yOASqLXCFmH8rHiDFY5aK5IF9dZ2OI5aQ21Vbh1eP8=; b=L5Xj8Mr0H0UHzm1fiK7JIBglX5yjWuxiDyQDWJKBReq+oVHHyAVG4rZYz/nrx6HAkX +zutx2gBIS7qbDS2Wkk8LuAhA4tEiFPjXSlWSgSdR9SzSMasmiWbdVAPewI65aBm7EEd VDmo5vr5mbZgdi39QIzgvag2Y1HnuGmgzwgPIhXhQ9+5ujUcT61V9bQQWl9BIgHZqoxA uemkh/bSm0tnUbD4Cz81TaWUY38xhSnzj4doHXuIhcpcpUmUU3GGKvMakAMMrqCYTPag IXLNjdfn0x7988uCkgulOT8qNNMZOtKbE4VMH+eSXgBz81LedSl7c7gDwtIaenDyzB+7 irfg== X-Gm-Message-State: AOAM533RHJM98ALhpcnm1fqWPruQpCvZ90S/q1B9ScEb6X6LyDwzgaF2 c3QcDSUKiszIDKBZFiHd39SGAg== X-Google-Smtp-Source: ABdhPJy/l5JCoFPdFR12hWOnKrP/lLjwYszhjP/WNJBh99XAQ0ifkW1xWHqHas6EDvPBSGX8HpJRMQ== X-Received: by 2002:a63:8f19:: with SMTP id n25mr3154262pgd.17.1610560917380; Wed, 13 Jan 2021 10:01:57 -0800 (PST) Date: Wed, 13 Jan 2021 10:01:55 -0800 From: Kees Cook To: "Eric W. Biederman" Cc: Alexey Gladkov , LKML , Linux Containers , Kernel Hardening , Alexey Gladkov , Christian Brauner , Linus Torvalds Subject: Re: [RFC PATCH v2 1/8] Use atomic type for ucounts reference counting Message-ID: <202101131001.BF1108F90@keescook> References: <447547b12bba1894d3f1f79d6408dfc60b219b0c.1610299857.git.gladkov.alexey@gmail.com> <878s8wdcib.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 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 > > --- > > 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