Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752556AbdGRKj0 (ORCPT ); Tue, 18 Jul 2017 06:39:26 -0400 Received: from mga02.intel.com ([134.134.136.20]:47629 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752385AbdGRKha (ORCPT ); Tue, 18 Jul 2017 06:37:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,377,1496127600"; d="scan'208";a="994241259" From: Elena Reshetova To: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, peterz@infradead.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, tj@kernel.org, mingo@redhat.com, hannes@cmpxchg.org, lizefan@huawei.com, acme@kernel.org, alexander.shishkin@linux.intel.com, eparis@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, luto@kernel.org, keescook@chromium.org, tglx@linutronix.de, dvhart@infradead.org, ebiederm@xmission.com, Elena Reshetova Subject: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t Date: Tue, 18 Jul 2017 13:30:07 +0300 Message-Id: <1500373808-8089-15-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1500373808-8089-1-git-send-email-elena.reshetova@intel.com> References: <1500373808-8089-1-git-send-email-elena.reshetova@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2965 Lines: 94 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 futex_pi_state.refcount 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 --- kernel/futex.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 16dbe4c..1cc7641 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -67,6 +67,7 @@ #include #include #include +#include #include @@ -209,7 +210,7 @@ struct futex_pi_state { struct rt_mutex pi_mutex; struct task_struct *owner; - atomic_t refcount; + refcount_t refcount; union futex_key key; } __randomize_layout; @@ -794,7 +795,7 @@ static int refill_pi_state_cache(void) INIT_LIST_HEAD(&pi_state->list); /* pi_mutex gets initialized later */ pi_state->owner = NULL; - atomic_set(&pi_state->refcount, 1); + refcount_set(&pi_state->refcount, 1); pi_state->key = FUTEX_KEY_INIT; current->pi_state_cache = pi_state; @@ -814,7 +815,7 @@ static struct futex_pi_state *alloc_pi_state(void) static void get_pi_state(struct futex_pi_state *pi_state) { - WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount)); + refcount_inc(&pi_state->refcount); } /* @@ -828,7 +829,7 @@ static void put_pi_state(struct futex_pi_state *pi_state) if (!pi_state) return; - if (!atomic_dec_and_test(&pi_state->refcount)) + if (!refcount_dec_and_test(&pi_state->refcount)) return; /* @@ -852,7 +853,7 @@ static void put_pi_state(struct futex_pi_state *pi_state) * refcount is at 0 - put it back to 1. */ pi_state->owner = NULL; - atomic_set(&pi_state->refcount, 1); + refcount_set(&pi_state->refcount, 1); current->pi_state_cache = pi_state; } } @@ -1046,7 +1047,7 @@ static int attach_to_pi_state(u32 __user *uaddr, u32 uval, * and futex_wait_requeue_pi() as it cannot go to 0 and consequently * free pi_state before we can take a reference ourselves. */ - WARN_ON(!atomic_read(&pi_state->refcount)); + WARN_ON(!refcount_read(&pi_state->refcount)); /* * Now that we have a pi_state, we can acquire wait_lock -- 2.7.4