linux-kernel - Re: [PATCH v4 27/30] fs: Add iput() cleanup helper

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Message-ID: <CAG48ez25VjcbUUkJiPru42LEX9AbUp0tfVrAcujo15ebozb0ew@mail.gmail.com>
Date: Mon, 13 Jan 2025 15:00:20 +0100
From: Jann Horn <jannh@...gle.com>
To: Mickaël Salaün <mic@...ikod.net>, 
	Christian Brauner <brauner@...nel.org>, Al Viro <viro@...iv.linux.org.uk>
Cc: Eric Paris <eparis@...hat.com>, Paul Moore <paul@...l-moore.com>, 
	Günther Noack <gnoack@...gle.com>, 
	"Serge E . Hallyn" <serge@...lyn.com>, Ben Scarlato <akhna@...gle.com>, 
	Casey Schaufler <casey@...aufler-ca.com>, Charles Zaffery <czaffery@...lox.com>, 
	Daniel Burgener <dburgener@...ux.microsoft.com>, 
	Francis Laniel <flaniel@...ux.microsoft.com>, James Morris <jmorris@...ei.org>, 
	Jeff Xu <jeffxu@...gle.com>, Jorge Lucangeli Obes <jorgelo@...gle.com>, Kees Cook <kees@...nel.org>, 
	Konstantin Meskhidze <konstantin.meskhidze@...wei.com>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Mikhail Ivanov <ivanov.mikhail1@...wei-partners.com>, Phil Sutter <phil@....cc>, 
	Praveen K Paladugu <prapal@...ux.microsoft.com>, Robert Salvet <robert.salvet@...lox.com>, 
	Shervin Oloumi <enlightened@...gle.com>, Song Liu <song@...nel.org>, 
	Tahera Fahimi <fahimitahera@...il.com>, Tyler Hicks <code@...icks.com>, audit@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org, 
	Jeff Layton <jlayton@...nel.org>, Josef Bacik <josef@...icpanda.com>
Subject: Re: [PATCH v4 27/30] fs: Add iput() cleanup helper

On Wed, Jan 8, 2025 at 4:44 PM Mickaël Salaün <mic@...ikod.net> wrote:
> Add a simple scope-based helper to put an inode reference, similar to
> the fput() helper.

Cleaning up inode references with scope-based cleanup seems dangerous
to me because, unlike most resources, holding a reference to an inode
beyond the lifetime of the associated superblock can actually cause
memory corruption; and scope-based cleanup is designed based on the
idea that the order and precise location of dropping a reference don't
matter so much.

So I would prefer to either not do this, or at least have some big
warning comment about usage requirements of scope-based inode
references.