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Date: Thu, 20 Feb 2020 23:03:09 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	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 4/7] proc: Use d_invalidate in proc_prune_siblings_dcache

On Thu, Feb 20, 2020 at 10:54:20PM +0000, Al Viro wrote:
> On Thu, Feb 20, 2020 at 02:49:53PM -0600, Eric W. Biederman wrote:
> > 
> > The function d_prune_aliases has the problem that it will only prune
> > aliases thare are completely unused.  It will not remove aliases for
> > the dcache or even think of removing mounts from the dcache.  For that
> > behavior d_invalidate is needed.
> > 
> > To use d_invalidate replace d_prune_aliases with d_find_alias
> > followed by d_invalidate and dput.  This is safe and complete
> > because no inode in proc has any hardlinks or aliases.
> 
> s/no inode.*/it's a fucking directory inode./

Wait... You are using it for sysctls as well?  Ho-hum...  The thing is,
for sysctls you are likely to run into consequent entries with the
same superblock, making for a big pile of useless playing with
->s_active...  And yes, that applied to mainline as well

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