From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Jan Kratochvil <jan.kratochvil@redhat.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Pedro Alves <palves@redhat.com>,
Simon Marchi <simon.marchi@efficios.com>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RESEND2] ptrace: make ptrace() fail if the tracee changed its pid unexpectedly
Date: Wed, 12 May 2021 09:56:49 -0400 (EDT) [thread overview]
Message-ID: <1879292286.40455.1620827809948.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20210512133615.GA19594@redhat.com>
----- On May 12, 2021, at 9:36 AM, Oleg Nesterov oleg@redhat.com wrote:
> On 05/11, Oleg Nesterov wrote:
>>
>> On 05/11, Oleg Nesterov wrote:
>> >
>> > On 05/11, Linus Torvalds wrote:
>> >
>> > > That said, why this:
>> > >
>> > > > + rcu_read_lock();
>> > > > + pid = task_pid_nr_ns(task, task_active_pid_ns(task->parent));
>> > > > + rcu_read_unlock();
>> > >
>> > > I don't see why the RCU read lock would be needed? task_pid_nr_ns()
>> > > does any required locking itself, afaik.
>> > >
>> > > And even if it wasn't, this all happens with siglock held, can
>> > > anything actually change.
>> >
>> > ... and with tasklist_lock held.
>> >
>> > Hmm. Linus, I am shy to admit I can't answer immediately, I'll recheck
>> > tomorrow after sleep. But it seems you are right.
>>
>> most probably to protect task->parent, not sure, this was 6 month ago...
>> but in this case we can use "current". I'll recheck.
>
> Of course you are right, rcu_read_lock() is not needed. Plus we can use
> task_pid_vnr() rather than task_pid_nr_ns(). I've sent v2.
Out of curiosity: what makes it OK to use either the current task or its
parent's pid namespace in this specific case ? What happens if they are
in different pid namespaces ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2021-05-12 13:56 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 16:56 [PATCH RESEND2] ptrace: make ptrace() fail if the tracee changed its pid unexpectedly Oleg Nesterov
2021-05-11 17:28 ` Linus Torvalds
2021-05-11 17:53 ` Oleg Nesterov
2021-05-11 18:06 ` Oleg Nesterov
2021-05-12 13:36 ` Oleg Nesterov
2021-05-12 13:56 ` Mathieu Desnoyers [this message]
2021-05-12 14:38 ` Oleg Nesterov
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