kernel-hardening - Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances

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Message-ID: <CAHk-=wi+1CPShMFvJNPfnrJ8DD8uVKUOQ5TQzQUNGLUkeoahkg@mail.gmail.com>
Date: Wed, 12 Feb 2020 12:35:04 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, LKML <linux-kernel@...r.kernel.org>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux API <linux-api@...r.kernel.org>, 
	Linux FS Devel <linux-fsdevel@...r.kernel.org>, 
	Linux Security Module <linux-security-module@...r.kernel.org>, 
	Akinobu Mita <akinobu.mita@...il.com>, Alexey Dobriyan <adobriyan@...il.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, 
	Daniel Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>, 
	"Dmitry V . Levin" <ldv@...linux.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Ingo Molnar <mingo@...nel.org>, "J . Bruce Fields" <bfields@...ldses.org>, 
	Jeff Layton <jlayton@...chiereds.net>, Jonathan Corbet <corbet@....net>, 
	Kees Cook <keescook@...omium.org>, Oleg Nesterov <oleg@...hat.com>, 
	Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances

On Wed, Feb 12, 2020 at 12:03 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> What's to prevent racing with fs shutdown while you are doing the second part?

I was thinking that only the proc_flush_task() code would do this.

And that holds a ref to the vfsmount through upid->ns.

So I wasn't suggesting doing this in general - just splitting up the
implementation of d_invalidate() so that proc_flush_task_mnt() could
delay the complex part to after having traversed the RCU-protected
list.

But hey - I missed this part of the problem originally, so maybe I'm
just missing something else this time. Wouldn't be the first time.

               Linus

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