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From: Jann Horn <jannh@google.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kees Cook <keescook@chromium.org>,
	David Howells <dhowells@redhat.com>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access()
Date: Wed, 29 May 2019 23:02:37 +0200	[thread overview]
Message-ID: <CAG48ez3PCoZTqKeUJ-jLu8HtiXRf_mOcnC6AtgTc0QM0Q6VrSA@mail.gmail.com> (raw)
In-Reply-To: <20190529162120.GB27659@redhat.com>

On Wed, May 29, 2019 at 6:21 PM Oleg Nesterov <oleg@redhat.com> wrote:
> On 05/29, Jann Horn wrote:
> > --- a/kernel/ptrace.c
> > +++ b/kernel/ptrace.c
> > @@ -324,6 +324,16 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
[...]
> >       mm = task->mm;
>
> while at it, could you also change this into mm = READ_ONCE(task->mm) ?

Actually, that shouldn't be necessary. The caller of
__ptrace_may_access() holds the task_lock() on the task, and that
should prevent concurrent updates of ->mm. If concurrent updates of
->mm *were* possible, we'd probably be in deep trouble here (and by
that I mean use-after-free).

  parent reply	other threads:[~2019-05-29 21:03 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 11:31 Jann Horn
2019-05-29 15:59 ` Eric W. Biederman
2019-05-29 16:01   ` Jann Horn
2019-05-29 16:21 ` Oleg Nesterov
2019-05-29 17:38   ` Jann Horn
2019-05-30  1:41     ` Eric W. Biederman
2019-05-31 15:04       ` Jann Horn
2019-05-30 10:34     ` Andrea Parri
2019-05-31  9:08       ` Peter Zijlstra
2019-05-30 12:05     ` Oleg Nesterov
2019-05-31  9:12       ` Peter Zijlstra
2019-05-31  9:55         ` Oleg Nesterov
2019-05-29 21:02   ` Jann Horn [this message]
2019-05-29 18:55 ` Kees Cook
2019-05-30 12:34 ` Oleg Nesterov
2019-05-31 11:56   ` Jann Horn
2019-05-31 13:35     ` Oleg Nesterov
2019-05-31 19:37       ` Jann Horn

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