Message-Id: <200912100229.nBA2TfTH008226@www262.sakura.ne.jp>
Subject: Re: [patch 1/9] sys: Fix missing rcu protection for __task_cred() access
From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: paulmck@linux.vnet.ibm.com
Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org,
       tglx@linutronix.de
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Date: Thu, 10 Dec 2009 11:29:41 +0900
References: <20091210001308.247025548@linutronix.de> <20091210004703.029784964@linutronix.de> <20091210012517.GF6938@linux.vnet.ibm.com>
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> 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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