linux-kernel - Re: [patch 1/9] sys: Fix missing rcu protection for __task

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Message-Id: <200912100229.nBA2TfTH008226@www262.sakura.ne.jp>
Date:	Thu, 10 Dec 2009 11:29:41 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, tglx@...utronix.de
Subject: Re: [patch 1/9] sys: Fix missing rcu protection for __task_cred() access

> As a rough rule of thumb, any dereference of an RCU-protected
> pointer must be covered by rcu_read_lock() or rcu_read_lock_bh()
> or by the appropriate update-side lock.

Does this mean that we need both rcu_read_lock() *and*
read_lock(&tasklist_lock) when calling find_task_by_vpid() because pid_task()
uses rcu_dereference() and find_pid_ns() uses hlist_for_each_entry_rcu ?

378 /*
379  * Must be called under rcu_read_lock() or with tasklist_lock read-held.
380  */
381 struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
382 {
383         return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
384 }
385 
386 struct task_struct *find_task_by_vpid(pid_t vnr)
387 {
388         return find_task_by_pid_ns(vnr, current->nsproxy->pid_ns);
389 }
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