Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 20 Feb 2020 23:03:09 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux Security Module <linux-security-module@vger.kernel.org>,
        Akinobu Mita <akinobu.mita@gmail.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Daniel Micay <danielmicay@gmail.com>,
        Djalal Harouni <tixxdz@gmail.com>,
        "Dmitry V . Levin" <ldv@altlinux.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@poochiereds.net>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Solar Designer <solar@openwall.com>
Subject: Re: [PATCH 4/7] proc: Use d_invalidate in proc_prune_siblings_dcache
Message-ID: <20200220230309.GS23230@ZenIV.linux.org.uk>
References: <CAHk-=wi+1CPShMFvJNPfnrJ8DD8uVKUOQ5TQzQUNGLUkeoahkg@mail.gmail.com>
 <20200212203833.GQ23230@ZenIV.linux.org.uk>
 <20200212204124.GR23230@ZenIV.linux.org.uk>
 <CAHk-=wi5FOGV_3tALK3n6E2fK3Oa_yCYkYQtCSaXLSEm2DUCKg@mail.gmail.com>
 <87lfp7h422.fsf@x220.int.ebiederm.org>
 <CAHk-=wgmn9Qds0VznyphouSZW6e42GWDT5H1dpZg8pyGDGN+=w@mail.gmail.com>
 <87pnejf6fz.fsf@x220.int.ebiederm.org>
 <871rqpaswu.fsf_-_@x220.int.ebiederm.org>
 <87blpt9e6m.fsf_-_@x220.int.ebiederm.org>
 <20200220225420.GR23230@ZenIV.linux.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200220225420.GR23230@ZenIV.linux.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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