Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752081AbdGRKgv (ORCPT ); Tue, 18 Jul 2017 06:36:51 -0400 Received: from mga04.intel.com ([192.55.52.120]:57036 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752014AbdGRKgs (ORCPT ); Tue, 18 Jul 2017 06:36:48 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,377,1496127600"; d="scan'208";a="994241057" 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 06/15] sched/task_struct: convert task_struct.stack_refcount to refcount_t Date: Tue, 18 Jul 2017 13:29:59 +0300 Message-Id: <1500373808-8089-7-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: 3786 Lines: 108 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.stack_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 --- include/linux/init_task.h | 3 ++- include/linux/sched.h | 2 +- include/linux/sched/task_stack.h | 2 +- kernel/fork.c | 6 +++--- 4 files changed, 7 insertions(+), 6 deletions(-) diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 7ba3fca..8be9369 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -214,7 +215,7 @@ extern struct cred init_cred; #ifdef CONFIG_THREAD_INFO_IN_TASK # define INIT_TASK_TI(tsk) \ .thread_info = INIT_THREAD_INFO(tsk), \ - .stack_refcount = ATOMIC_INIT(1), + .stack_refcount = REFCOUNT_INIT(1), #else # define INIT_TASK_TI(tsk) #endif diff --git a/include/linux/sched.h b/include/linux/sched.h index 9380e44..bd49917 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1078,7 +1078,7 @@ struct task_struct { #endif #ifdef CONFIG_THREAD_INFO_IN_TASK /* A live task holds one reference: */ - atomic_t stack_refcount; + refcount_t stack_refcount; #endif #ifdef CONFIG_LIVEPATCH int patch_state; diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h index df6ea66..aab3809 100644 --- a/include/linux/sched/task_stack.h +++ b/include/linux/sched/task_stack.h @@ -60,7 +60,7 @@ static inline unsigned long *end_of_stack(struct task_struct *p) #ifdef CONFIG_THREAD_INFO_IN_TASK static inline void *try_get_task_stack(struct task_struct *tsk) { - return atomic_inc_not_zero(&tsk->stack_refcount) ? + return refcount_inc_not_zero(&tsk->stack_refcount) ? task_stack_page(tsk) : NULL; } diff --git a/kernel/fork.c b/kernel/fork.c index cfd8a42..6fd6be0 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -354,7 +354,7 @@ static void release_task_stack(struct task_struct *tsk) #ifdef CONFIG_THREAD_INFO_IN_TASK void put_task_stack(struct task_struct *tsk) { - if (atomic_dec_and_test(&tsk->stack_refcount)) + if (refcount_dec_and_test(&tsk->stack_refcount)) release_task_stack(tsk); } #endif @@ -372,7 +372,7 @@ void free_task(struct task_struct *tsk) * If the task had a separate stack allocation, it should be gone * by now. */ - WARN_ON_ONCE(atomic_read(&tsk->stack_refcount) != 0); + WARN_ON_ONCE(refcount_read(&tsk->stack_refcount) != 0); #endif rt_mutex_debug_task_free(tsk); ftrace_graph_exit_task(tsk); @@ -532,7 +532,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) tsk->stack_vm_area = stack_vm_area; #endif #ifdef CONFIG_THREAD_INFO_IN_TASK - atomic_set(&tsk->stack_refcount, 1); + refcount_set(&tsk->stack_refcount, 1); #endif if (err) -- 2.7.4