Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753414Ab3H0R2d (ORCPT ); Tue, 27 Aug 2013 13:28:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18171 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753309Ab3H0R2c (ORCPT ); Tue, 27 Aug 2013 13:28:32 -0400 Date: Tue, 27 Aug 2013 19:21:55 +0200 From: Oleg Nesterov To: Richard Guy Briggs Cc: linux-audit@redhat.com, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Eric Paris , Al Viro , Ingo Molnar , Peter Zijlstra , "Serge E. Hallyn" , John Johansen , James Morris , Andrew Morton , Kentaro Takeda , Tetsuo Handa , Greg Kroah-Hartman , Jiri Slaby Subject: Re: [PATCH 03/12] pid: get ppid pid_t of task in init_pid_ns safely Message-ID: <20130827172155.GC29147@redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1303 Lines: 47 On 08/20, Richard Guy Briggs wrote: > > Added the functions > task_ppid() > task_ppid_nr_ns() > task_ppid_nr_init_ns() > to safely abstract the lookup of the PPID but it is not safe. > +static inline struct pid *task_ppid(struct task_struct *task) > +{ > + return task_tgid(rcu_dereference(current->real_parent)); ^^^^^^^ task? > +static inline pid_t task_ppid_nr_ns(struct task_struct *tsk, > + struct pid_namespace *ns) > +{ > + pid_t pid; > + > + rcu_read_lock(); > + pid = pid_nr_ns(task_ppid(current), ns); ^^^^^^^ again. > + rcu_read_unlock(); And why this is safe? rcu_read_lock() can't help if tsk was already dead _before_ it takes the rcu lock. ->real_parent can point the already freed/reused/unmapped memory. This is safe if, for example, the caller alredy holds rcu_read_lock() and tsk was found by find_task_by*(), or tsk is current. Richard, just in case... I am going to vacation, I will be completely offline till Sep 10. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/