From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga07.intel.com ([134.134.136.100]:7859 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752211AbdJTIQb (ORCPT ); Fri, 20 Oct 2017 04:16:31 -0400 From: Elena Reshetova To: axboe@kernel.dk Cc: james.bottomley@hansenpartnership.com, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-btrfs@vger.kernel.org, peterz@infradead.org, gregkh@linuxfoundation.org, fujita.tomonori@lab.ntt.co.jp, mingo@redhat.com, clm@fb.com, jbacik@fb.com, dsterba@suse.com, keescook@chromium.org, Elena Reshetova Subject: [PATCH 6/6] drivers, block: convert xen_blkif.refcnt from atomic_t to refcount_t Date: Fri, 20 Oct 2017 11:16:02 +0300 Message-Id: <1508487362-26663-7-git-send-email-elena.reshetova@intel.com> In-Reply-To: <1508487362-26663-1-git-send-email-elena.reshetova@intel.com> References: <1508487362-26663-1-git-send-email-elena.reshetova@intel.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: 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 xen_blkif.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 --- drivers/block/xen-blkback/common.h | 7 ++++--- drivers/block/xen-blkback/xenbus.c | 2 +- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index ecb35fe..0c3320d 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -35,6 +35,7 @@ #include #include #include +#include #include #include #include @@ -319,7 +320,7 @@ struct xen_blkif { struct xen_vbd vbd; /* Back pointer to the backend_info. */ struct backend_info *be; - atomic_t refcnt; + refcount_t refcnt; /* for barrier (drain) requests */ struct completion drain_complete; atomic_t drain; @@ -372,10 +373,10 @@ struct pending_req { (_v)->bdev->bd_part->nr_sects : \ get_capacity((_v)->bdev->bd_disk)) -#define xen_blkif_get(_b) (atomic_inc(&(_b)->refcnt)) +#define xen_blkif_get(_b) (refcount_inc(&(_b)->refcnt)) #define xen_blkif_put(_b) \ do { \ - if (atomic_dec_and_test(&(_b)->refcnt)) \ + if (refcount_dec_and_test(&(_b)->refcnt)) \ schedule_work(&(_b)->free_work);\ } while (0) diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 21c1be1..5955b61 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -176,7 +176,7 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid) return ERR_PTR(-ENOMEM); blkif->domid = domid; - atomic_set(&blkif->refcnt, 1); + refcount_set(&blkif->refcnt, 1); init_completion(&blkif->drain_complete); INIT_WORK(&blkif->free_work, xen_blkif_deferred_free); -- 2.7.4