From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga07.intel.com ([134.134.136.100]:27837 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752414AbdJTIQV (ORCPT ); Fri, 20 Oct 2017 04:16:21 -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 3/6] block: convert blkcg_gq.refcnt from atomic_t to refcount_t Date: Fri, 20 Oct 2017 11:15:59 +0300 Message-Id: <1508487362-26663-4-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 blkcg_gq.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 --- block/blk-cgroup.c | 2 +- include/linux/blk-cgroup.h | 11 ++++++----- 2 files changed, 7 insertions(+), 6 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index d3f56ba..1e7cedc 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -107,7 +107,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q, blkg->q = q; INIT_LIST_HEAD(&blkg->q_node); blkg->blkcg = blkcg; - atomic_set(&blkg->refcnt, 1); + refcount_set(&blkg->refcnt, 1); /* root blkg uses @q->root_rl, init rl only for !root blkgs */ if (blkcg != &blkcg_root) { diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 9d92153..c95d29d 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -19,6 +19,7 @@ #include #include #include +#include /* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */ #define BLKG_STAT_CPU_BATCH (INT_MAX / 2) @@ -122,7 +123,7 @@ struct blkcg_gq { struct request_list rl; /* reference count */ - atomic_t refcnt; + refcount_t refcnt; /* is this blkg online? protected by both blkcg and q locks */ bool online; @@ -354,8 +355,8 @@ static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen) */ static inline void blkg_get(struct blkcg_gq *blkg) { - WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0); - atomic_inc(&blkg->refcnt); + WARN_ON_ONCE(refcount_read(&blkg->refcnt) == 0); + refcount_inc(&blkg->refcnt); } void __blkg_release_rcu(struct rcu_head *rcu); @@ -366,8 +367,8 @@ void __blkg_release_rcu(struct rcu_head *rcu); */ static inline void blkg_put(struct blkcg_gq *blkg) { - WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0); - if (atomic_dec_and_test(&blkg->refcnt)) + WARN_ON_ONCE(refcount_read(&blkg->refcnt) == 0); + if (refcount_dec_and_test(&blkg->refcnt)) call_rcu(&blkg->rcu_head, __blkg_release_rcu); } -- 2.7.4