Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751511AbdH3MXK (ORCPT ); Wed, 30 Aug 2017 08:23:10 -0400 Received: from mga02.intel.com ([134.134.136.20]:15882 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751302AbdH3MXG (ORCPT ); Wed, 30 Aug 2017 08:23:06 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.41,448,1498546800"; d="scan'208";a="895512072" 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 01/15] sched: convert sighand_struct.count to refcount_t Date: Wed, 30 Aug 2017 15:22:39 +0300 Message-Id: <1504095773-22895-2-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1504095773-22895-1-git-send-email-elena.reshetova@intel.com> References: <1504095773-22895-1-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: 4750 Lines: 138 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. 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 daa19d8..5c8960d 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1200,7 +1200,7 @@ 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 @@ -1210,7 +1210,7 @@ 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 8652209..5038b6b 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -63,7 +63,7 @@ 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 3c07ace..6c6f520 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -85,7 +85,7 @@ 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 2a0dd40..4d5cdf1 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -7,13 +7,14 @@ #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 8004fc7..43bcd20 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1320,7 +1320,7 @@ 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); @@ -1328,14 +1328,14 @@ 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 @@ -2236,7 +2236,7 @@ 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) { -- 2.7.4