Date: Wed, 16 Aug 2006 22:19:50 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       containers@lists.osdl.org
Subject: Re: [PATCH 5/7] pid: Implement pid_nr
Message-ID: <20060816181950.GA472@oleg>
References: <m1k65997xk.fsf@ebiederm.dsl.xmission.com> <1155666193751-git-send-email-ebiederm@xmission.com>
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On 08/15, Eric W. Biederman wrote:
>
> +static inline pid_t pid_nr(struct pid *pid)
> +{
> +	pid_t nr = 0;
> +	if (pid)
> +		nr = pid->nr;
> +	return nr;
> +}

I think this is not safe, you need rcu locks here or the caller should
do some locking.

Let's look at f_getown() (PATCH 7/7). What if original task which was
pointed by ->f_owner.pid has gone, another thread does fcntl(F_SETOWN),
and pid_nr() takes a preemtion after 'if (pid)'? In this case 'pid->nr'
may follow a freed memory.

Oleg.

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