From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [patch 2/2] proc_fork_connector: a lockless ->real_parent usage is not safe Date: Thu, 28 Jul 2011 13:54:25 -0700 Message-ID: <201107282054.p6SKsPtJ007979@imap1.linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ASCII Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org, akpm@linux-foundation.org, oleg@redhat.com, johnpol@2ka.mipt.ru, vzapolskiy@gmail.com, zbr@ioremap.net To: davem@davemloft.net Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:48773 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755177Ab1G1Uyl (ORCPT ); Thu, 28 Jul 2011 16:54:41 -0400 Sender: netdev-owner@vger.kernel.org List-ID: From: Oleg Nesterov proc_fork_connector() uses ->real_parent lockless. This is not safe if copy_process() was called with CLONE_THREAD or CLONE_PARENT, in this case the parent != current can go away at any moment. Signed-off-by: Oleg Nesterov Cc: Vladimir Zapolskiy Cc: "David S. Miller" Cc: Evgeniy Polyakov Cc: Evgeniy Polyakov Signed-off-by: Andrew Morton --- drivers/connector/cn_proc.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff -puN drivers/connector/cn_proc.c~proc_fork_connector-a-lockless-real_parent-usage-is-not-safe drivers/connector/cn_proc.c --- a/drivers/connector/cn_proc.c~proc_fork_connector-a-lockless-real_parent-usage-is-not-safe +++ a/drivers/connector/cn_proc.c @@ -57,6 +57,7 @@ void proc_fork_connector(struct task_str struct proc_event *ev; __u8 buffer[CN_PROC_MSG_SIZE]; struct timespec ts; + struct task_struct *parent; if (atomic_read(&proc_event_num_listeners) < 1) return; @@ -67,8 +68,11 @@ void proc_fork_connector(struct task_str ktime_get_ts(&ts); /* get high res monotonic timestamp */ put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns); ev->what = PROC_EVENT_FORK; - ev->event_data.fork.parent_pid = task->real_parent->pid; - ev->event_data.fork.parent_tgid = task->real_parent->tgid; + rcu_read_lock(); + parent = rcu_dereference(task->real_parent); + ev->event_data.fork.parent_pid = parent->pid; + ev->event_data.fork.parent_tgid = parent->tgid; + rcu_read_unlock(); ev->event_data.fork.child_pid = task->pid; ev->event_data.fork.child_tgid = task->tgid; _