From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752963AbdJTQVP (ORCPT ); Fri, 20 Oct 2017 12:21:15 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:41236 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752322AbdJTQVN (ORCPT ); Fri, 20 Oct 2017 12:21:13 -0400 Subject: Re: [PATCH] sparc64: convert mdesc_handle.refcnt from atomic_t to refcount_t To: Elena Reshetova , davem@davemloft.net Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, jag.raman@oracle.com, peterz@infradead.org, keescook@chromium.org References: <1508486277-24913-1-git-send-email-elena.reshetova@intel.com> From: Shannon Nelson Organization: Oracle Corporation Message-ID: <519f48f1-3145-6bf4-469f-0c6059681287@oracle.com> Date: Fri, 20 Oct 2017 09:20:26 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1508486277-24913-1-git-send-email-elena.reshetova@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/20/2017 12:57 AM, Elena Reshetova wrote: > atomic_t variables are currently used to implement reference > counters with the following properties: > - counter is initialized to 1 using atomic_set() > - a resource is freed upon counter reaching zero > - once counter reaches zero, its further > increments aren't allowed > - counter schema uses basic atomic operations > (set, inc, inc_not_zero, dec_and_test, etc.) > > Such atomic variables should be converted to a newly provided > refcount_t type and API that prevents accidental counter overflows > and underflows. This is important since overflows and underflows > can lead to use-after-free situation and be exploitable. > > The variable mdesc_handle.refcnt is used as pure reference counter. > Convert it to refcount_t and fix up the operations. > > Suggested-by: Kees Cook > Reviewed-by: David Windsor > Reviewed-by: Hans Liljestrand > Signed-off-by: Elena Reshetova Acked-by: Shannon Nelson > --- > arch/sparc/kernel/mdesc.c | 17 +++++++++-------- > 1 file changed, 9 insertions(+), 8 deletions(-) > > diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c > index fa466ce..821a724 100644 > --- a/arch/sparc/kernel/mdesc.c > +++ b/arch/sparc/kernel/mdesc.c > @@ -12,6 +12,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -70,7 +71,7 @@ struct mdesc_handle { > struct list_head list; > struct mdesc_mem_ops *mops; > void *self_base; > - atomic_t refcnt; > + refcount_t refcnt; > unsigned int handle_size; > struct mdesc_hdr mdesc; > }; > @@ -152,7 +153,7 @@ static void mdesc_handle_init(struct mdesc_handle *hp, > memset(hp, 0, handle_size); > INIT_LIST_HEAD(&hp->list); > hp->self_base = base; > - atomic_set(&hp->refcnt, 1); > + refcount_set(&hp->refcnt, 1); > hp->handle_size = handle_size; > } > > @@ -182,7 +183,7 @@ static void __init mdesc_memblock_free(struct mdesc_handle *hp) > unsigned int alloc_size; > unsigned long start; > > - BUG_ON(atomic_read(&hp->refcnt) != 0); > + BUG_ON(refcount_read(&hp->refcnt) != 0); > BUG_ON(!list_empty(&hp->list)); > > alloc_size = PAGE_ALIGN(hp->handle_size); > @@ -220,7 +221,7 @@ static struct mdesc_handle *mdesc_kmalloc(unsigned int mdesc_size) > > static void mdesc_kfree(struct mdesc_handle *hp) > { > - BUG_ON(atomic_read(&hp->refcnt) != 0); > + BUG_ON(refcount_read(&hp->refcnt) != 0); > BUG_ON(!list_empty(&hp->list)); > > kfree(hp->self_base); > @@ -259,7 +260,7 @@ struct mdesc_handle *mdesc_grab(void) > spin_lock_irqsave(&mdesc_lock, flags); > hp = cur_mdesc; > if (hp) > - atomic_inc(&hp->refcnt); > + refcount_inc(&hp->refcnt); > spin_unlock_irqrestore(&mdesc_lock, flags); > > return hp; > @@ -271,7 +272,7 @@ void mdesc_release(struct mdesc_handle *hp) > unsigned long flags; > > spin_lock_irqsave(&mdesc_lock, flags); > - if (atomic_dec_and_test(&hp->refcnt)) { > + if (refcount_dec_and_test(&hp->refcnt)) { > list_del_init(&hp->list); > hp->mops->free(hp); > } > @@ -513,7 +514,7 @@ void mdesc_update(void) > if (status != HV_EOK || real_len > len) { > printk(KERN_ERR "MD: mdesc reread fails with %lu\n", > status); > - atomic_dec(&hp->refcnt); > + refcount_dec(&hp->refcnt); > mdesc_free(hp); > goto out; > } > @@ -526,7 +527,7 @@ void mdesc_update(void) > mdesc_notify_clients(orig_hp, hp); > > spin_lock_irqsave(&mdesc_lock, flags); > - if (atomic_dec_and_test(&orig_hp->refcnt)) > + if (refcount_dec_and_test(&orig_hp->refcnt)) > mdesc_free(orig_hp); > else > list_add(&orig_hp->list, &mdesc_zombie_list); >