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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 1B663C43387 for ; Fri, 18 Jan 2019 12:28:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7DF32087E for ; Fri, 18 Jan 2019 12:27:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727755AbfARM16 (ORCPT ); Fri, 18 Jan 2019 07:27:58 -0500 Received: from mga05.intel.com ([192.55.52.43]:2175 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727679AbfARM15 (ORCPT ); Fri, 18 Jan 2019 07:27:57 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Jan 2019 04:27:56 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,491,1539673200"; d="scan'208";a="268136120" Received: from elena-thinkpad-x230.fi.intel.com ([10.237.68.34]) by orsmga004.jf.intel.com with ESMTP; 18 Jan 2019 04:27:53 -0800 From: Elena Reshetova To: mingo@redhat.com Cc: peterz@infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, keescook@chromium.org, tglx@linutronix.de, Elena Reshetova Subject: [PATCH 4/5] sched/task_struct: convert task_struct.usage to refcount_t Date: Fri, 18 Jan 2019 14:27:29 +0200 Message-Id: <1547814450-18902-5-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1547814450-18902-1-git-send-email-elena.reshetova@intel.com> References: <1547814450-18902-1-git-send-email-elena.reshetova@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 task_struct.usage 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 task_struct.usage it might make a difference in following places: - put_task_struct(): 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 --- include/linux/sched.h | 3 ++- include/linux/sched/task.h | 4 ++-- init/init_task.c | 2 +- kernel/fork.c | 4 ++-- 4 files changed, 7 insertions(+), 6 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 5e66900..bead0c7 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -21,6 +21,7 @@ #include #include #include +#include #include #include #include @@ -608,7 +609,7 @@ struct task_struct { randomized_struct_fields_start void *stack; - atomic_t usage; + refcount_t usage; /* Per task flags (PF_*), defined further below: */ unsigned int flags; unsigned int ptrace; diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index 44c6f15..2e97a22 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -88,13 +88,13 @@ extern void sched_exec(void); #define sched_exec() {} #endif -#define get_task_struct(tsk) do { atomic_inc(&(tsk)->usage); } while(0) +#define get_task_struct(tsk) do { refcount_inc(&(tsk)->usage); } while(0) extern void __put_task_struct(struct task_struct *t); static inline void put_task_struct(struct task_struct *t) { - if (atomic_dec_and_test(&t->usage)) + if (refcount_dec_and_test(&t->usage)) __put_task_struct(t); } diff --git a/init/init_task.c b/init/init_task.c index 756be60..0ad9772 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -66,7 +66,7 @@ struct task_struct init_task #endif .state = 0, .stack = init_stack, - .usage = ATOMIC_INIT(2), + .usage = REFCOUNT_INIT(2), .flags = PF_KTHREAD, .prio = MAX_PRIO - 20, .static_prio = MAX_PRIO - 20, diff --git a/kernel/fork.c b/kernel/fork.c index 504324c..a4ac220 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -716,7 +716,7 @@ static inline void put_signal_struct(struct signal_struct *sig) void __put_task_struct(struct task_struct *tsk) { WARN_ON(!tsk->exit_state); - WARN_ON(atomic_read(&tsk->usage)); + WARN_ON(refcount_read(&tsk->usage)); WARN_ON(tsk == current); cgroup_free(tsk); @@ -895,7 +895,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) * One for us, one for whoever does the "release_task()" (usually * parent) */ - atomic_set(&tsk->usage, 2); + refcount_set(&tsk->usage, 2); #ifdef CONFIG_BLK_DEV_IO_TRACE tsk->btrace_seq = 0; #endif -- 2.7.4