From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0F53C282D7 for ; Mon, 4 Feb 2019 08:54:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 710BA20820 for ; Mon, 4 Feb 2019 08:54:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728560AbfBDIyT (ORCPT ); Mon, 4 Feb 2019 03:54:19 -0500 Received: from terminus.zytor.com ([198.137.202.136]:45295 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728359AbfBDIyT (ORCPT ); Mon, 4 Feb 2019 03:54:19 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x148rntG357613 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Mon, 4 Feb 2019 00:53:49 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x148rlvw357608; Mon, 4 Feb 2019 00:53:47 -0800 Date: Mon, 4 Feb 2019 00:53:47 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Elena Reshetova Message-ID: Cc: andrea.parri@amarulasolutions.com, efault@gmx.de, mingo@kernel.org, dwindsor@gmail.com, tglx@linutronix.de, keescook@chromium.org, ishkamiel@gmail.com, peterz@infradead.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, elena.reshetova@intel.com, oleg@redhat.com, hpa@zytor.com Reply-To: andrea.parri@amarulasolutions.com, linux-kernel@vger.kernel.org, efault@gmx.de, torvalds@linux-foundation.org, elena.reshetova@intel.com, oleg@redhat.com, mingo@kernel.org, dwindsor@gmail.com, keescook@chromium.org, tglx@linutronix.de, ishkamiel@gmail.com, peterz@infradead.org, hpa@zytor.com In-Reply-To: <1547814450-18902-2-git-send-email-elena.reshetova@intel.com> References: <1547814450-18902-2-git-send-email-elena.reshetova@intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/core: Convert sighand_struct.count to refcount_t Git-Commit-ID: d036bda7d0e7269c2982eb979acfef855f5d7977 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: d036bda7d0e7269c2982eb979acfef855f5d7977 Gitweb: https://git.kernel.org/tip/d036bda7d0e7269c2982eb979acfef855f5d7977 Author: Elena Reshetova AuthorDate: Fri, 18 Jan 2019 14:27:26 +0200 Committer: Ingo Molnar CommitDate: Mon, 4 Feb 2019 08:53:52 +0100 sched/core: Convert sighand_struct.count to refcount_t 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 Signed-off-by: Elena Reshetova Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Reviewed-by: Andrea Parri Reviewed-by: Oleg Nesterov Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: akpm@linux-foundation.org Cc: viro@zeniv.linux.org.uk Link: https://lkml.kernel.org/r/1547814450-18902-2-git-send-email-elena.reshetova@intel.com Signed-off-by: Ingo Molnar --- fs/exec.c | 4 ++-- fs/proc/task_nommu.c | 2 +- include/linux/sched/signal.h | 3 ++- kernel/fork.c | 8 ++++---- 4 files changed, 9 insertions(+), 8 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index fb72d36f7823..966cd98a2ce2 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1189,7 +1189,7 @@ no_thread_group: 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 @@ -1199,7 +1199,7 @@ no_thread_group: 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 0b63d68dedb2..f912872fbf91 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/sched/signal.h b/include/linux/sched/signal.h index 13789d10a50e..37eeb1a28eba 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 b69248e6f0e0..370856d4c0b3 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1463,7 +1463,7 @@ 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); @@ -1471,7 +1471,7 @@ 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); spin_lock_irq(¤t->sighand->siglock); memcpy(sig->action, current->sighand->action, sizeof(sig->action)); spin_unlock_irq(¤t->sighand->siglock); @@ -1480,7 +1480,7 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) 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 @@ -2439,7 +2439,7 @@ 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) {