linux-kernel - Re: [PATCH] pids: make task_tgid_nr

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Message-ID: <20170821200520.GB32112@worktop.programming.kicks-ass.net>
Date:   Mon, 21 Aug 2017 22:05:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Troy Kensinger <tkensinger@...gle.com>,
        "security@...nel.org" <security@...nel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Josh Triplett <josh@...htriplett.org>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] pids: make task_tgid_nr_ns() safe

On Mon, Aug 21, 2017 at 05:35:02PM +0200, Oleg Nesterov wrote:
> This was reported many times, and this was even mentioned in commit
> 52ee2dfdd4f5 "pids: refactor vnr/nr_ns helpers to make them safe" but
> somehow nobody bothered to fix the obvious problem: task_tgid_nr_ns()
> is not safe because task->group_leader points to nowhere after the
> exiting task passes exit_notify(), rcu_read_lock() can not help.
> 
> We really need to change __unhash_process() to nullify group_leader,
> parent, and real_parent, but this needs some cleanups. Until then we
> can turn task_tgid_nr_ns() into another user of __task_pid_nr_ns() and
> fix the problem.
> 
> Reported-by: Troy Kensinger <tkensinger@...gle.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>