From patchwork Wed Nov 15 14:03:26 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Reshetova, Elena" X-Patchwork-Id: 10059441 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 42DED60231 for ; Wed, 15 Nov 2017 14:08:24 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3650E2A03B for ; Wed, 15 Nov 2017 14:08:24 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 2B3522A03D; Wed, 15 Nov 2017 14:08:24 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A19512A03B for ; Wed, 15 Nov 2017 14:08:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758019AbdKOOII (ORCPT ); Wed, 15 Nov 2017 09:08:08 -0500 Received: from mga11.intel.com ([192.55.52.93]:3897 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757983AbdKOOIA (ORCPT ); Wed, 15 Nov 2017 09:08:00 -0500 Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 15 Nov 2017 06:07:59 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,399,1505804400"; d="scan'208";a="2130959" Received: from elena-thinkpad-x230.fi.intel.com ([10.237.72.87]) by FMSMGA003.fm.intel.com with ESMTP; 15 Nov 2017 06:07:54 -0800 From: Elena Reshetova To: mingo@redhat.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, peterz@infradead.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, tj@kernel.org, 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, linux-mm@kvack.org, axboe@kernel.dk, Elena Reshetova Subject: [PATCH 02/16] sched: convert sighand_struct.count to refcount_t Date: Wed, 15 Nov 2017 16:03:26 +0200 Message-Id: <1510754620-27088-3-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1510754620-27088-1-git-send-email-elena.reshetova@intel.com> References: <1510754620-27088-1-git-send-email-elena.reshetova@intel.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 sighand_struct.count is used as pure reference counter. Convert it to refcount_t and fix up the operations. **Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. The full comparison can be seen in https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon in state to be merged to the documentation tree. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the sighand_struct.count it might make a difference in following places: - __cleanup_sighand: decrement in refcount_dec_and_test() only provides RELEASE ordering and control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Signed-off-by: Elena Reshetova --- fs/exec.c | 4 ++-- fs/proc/task_nommu.c | 2 +- include/linux/init_task.h | 2 +- include/linux/sched/signal.h | 3 ++- kernel/fork.c | 8 ++++---- 5 files changed, 10 insertions(+), 9 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 19e6325..09d99b5 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1181,7 +1181,7 @@ static int de_thread(struct task_struct *tsk) flush_itimer_signals(); #endif - if (atomic_read(&oldsighand->count) != 1) { + if (refcount_read(&oldsighand->count) != 1) { struct sighand_struct *newsighand; /* * This ->sighand is shared with the CLONE_SIGHAND @@ -1191,7 +1191,7 @@ static int de_thread(struct task_struct *tsk) if (!newsighand) return -ENOMEM; - atomic_set(&newsighand->count, 1); + refcount_set(&newsighand->count, 1); memcpy(newsighand->action, oldsighand->action, sizeof(newsighand->action)); diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c index 0b60ac6..684f808 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -64,7 +64,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm) else bytes += kobjsize(current->files); - if (current->sighand && atomic_read(¤t->sighand->count) > 1) + if (current->sighand && refcount_read(¤t->sighand->count) > 1) sbytes += kobjsize(current->sighand); else bytes += kobjsize(current->sighand); diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 6a53262..9eb2ce8 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -86,7 +86,7 @@ extern struct fs_struct init_fs; extern struct nsproxy init_nsproxy; #define INIT_SIGHAND(sighand) { \ - .count = ATOMIC_INIT(1), \ + .count = REFCOUNT_INIT(1), \ .action = { { { .sa_handler = SIG_DFL, } }, }, \ .siglock = __SPIN_LOCK_UNLOCKED(sighand.siglock), \ .signalfd_wqh = __WAIT_QUEUE_HEAD_INITIALIZER(sighand.signalfd_wqh), \ diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 64d85fc..4a0e2d8 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -8,13 +8,14 @@ #include #include #include +#include /* * Types defining task->signal and task->sighand and APIs using them: */ struct sighand_struct { - atomic_t count; + refcount_t count; struct k_sigaction action[_NSIG]; spinlock_t siglock; wait_queue_head_t signalfd_wqh; diff --git a/kernel/fork.c b/kernel/fork.c index a1db74e..be451af 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1381,7 +1381,7 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) struct sighand_struct *sig; if (clone_flags & CLONE_SIGHAND) { - atomic_inc(¤t->sighand->count); + refcount_inc(¤t->sighand->count); return 0; } sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL); @@ -1389,14 +1389,14 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) if (!sig) return -ENOMEM; - atomic_set(&sig->count, 1); + refcount_set(&sig->count, 1); memcpy(sig->action, current->sighand->action, sizeof(sig->action)); return 0; } void __cleanup_sighand(struct sighand_struct *sighand) { - if (atomic_dec_and_test(&sighand->count)) { + if (refcount_dec_and_test(&sighand->count)) { signalfd_cleanup(sighand); /* * sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it @@ -2303,7 +2303,7 @@ static int check_unshare_flags(unsigned long unshare_flags) return -EINVAL; } if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) { - if (atomic_read(¤t->sighand->count) > 1) + if (refcount_read(¤t->sighand->count) > 1) return -EINVAL; } if (unshare_flags & CLONE_VM) {