linux-kernel - Re: [PATCH v6 06/20] liveupdate: luo_file: implement file systems callbacks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aR9N14KWaz6SdFcw@kernel.org>
Date: Thu, 20 Nov 2025 19:20:23 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: pratyush@...nel.org, jasonmiu@...gle.com, graf@...zon.com,
	dmatlack@...gle.com, rientjes@...gle.com, corbet@....net,
	rdunlap@...radead.org, ilpo.jarvinen@...ux.intel.com,
	kanie@...ux.alibaba.com, ojeda@...nel.org, aliceryhl@...gle.com,
	masahiroy@...nel.org, akpm@...ux-foundation.org, tj@...nel.org,
	yoann.congal@...le.fr, mmaurer@...gle.com, roman.gushchin@...ux.dev,
	chenridong@...wei.com, axboe@...nel.dk, mark.rutland@....com,
	jannh@...gle.com, vincent.guittot@...aro.org, hannes@...xchg.org,
	dan.j.williams@...el.com, david@...hat.com,
	joel.granados@...nel.org, rostedt@...dmis.org,
	anna.schumaker@...cle.com, song@...nel.org, linux@...ssschuh.net,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-mm@...ck.org, gregkh@...uxfoundation.org, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	x86@...nel.org, hpa@...or.com, rafael@...nel.org, dakr@...nel.org,
	bartosz.golaszewski@...aro.org, cw00.choi@...sung.com,
	myungjoo.ham@...sung.com, yesanishhere@...il.com,
	Jonathan.Cameron@...wei.com, quic_zijuhu@...cinc.com,
	aleksander.lobakin@...el.com, ira.weiny@...el.com,
	andriy.shevchenko@...ux.intel.com, leon@...nel.org, lukas@...ner.de,
	bhelgaas@...gle.com, wagi@...nel.org, djeffery@...hat.com,
	stuart.w.hayes@...il.com, ptyadav@...zon.de, lennart@...ttering.net,
	brauner@...nel.org, linux-api@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, saeedm@...dia.com,
	ajayachandra@...dia.com, jgg@...dia.com, parav@...dia.com,
	leonro@...dia.com, witu@...dia.com, hughd@...gle.com,
	skhawaja@...gle.com, chrisl@...nel.org
Subject: Re: [PATCH v6 06/20] liveupdate: luo_file: implement file systems
 callbacks

On Mon, Nov 17, 2025 at 12:50:56PM -0500, Pasha Tatashin wrote:
> > > +struct liveupdate_file_handler;
> > > +struct liveupdate_session;
> >
> > Why struct liveupdate_session is a part of public LUO API?
> 
> It is an obscure version of private "struct luo_session", in order to
> give subsystem access to:
> liveupdate_get_file_incoming(s, token, filep)
> liveupdate_get_token_outgoing(s, file, tokenp)
> 
> For example, if your FD depends on another FD within a session, you
> can check if another FD is already preserved via
> liveupdate_get_token_outgoing(), and during retrieval time you can
> retrieve the "struct file" for your dependency.
 
And it's essentially unused right now.

> > > +     }
> > > +
> > > +     return 0;
> > > +
> > > +exit_err:
> > > +     fput(file);
> > > +     luo_session_free_files_mem(session);
> >
> > The error handling in this function is a mess. Pasha, please, please, use
> > goto consistently.
> 
> How is this a mess? There is a single exit_err destination, no
> exception, no early returns except at the very top of the function
> where we do early returns before fget() which makes total sense.
> 
> Do you want to add a separate destination for
> luo_session_free_files_mem() ? But that is not necessary, in many
> places it is considered totally reasonable for free(NULL) to work
> correctly...

You have a mix of releasing resources with goto or inside if (err).
And while basic free() primitives like kfree() and vfree() work correctly
with NULL as a parameter, luo_session_free_files_mem() is already not a
basic primitive and it may grow with a time. It already has two conditions
that essentially prevent anything from freeing and this will grow with the
time.

So yes, I want a separate goto destination for freeing each resource and a
goto for 

	err = fh->ops->preserve(&args);
	if (err)

case.

> > > +             luo_file = kzalloc(sizeof(*luo_file), GFP_KERNEL);
> > > +             if (!luo_file)
> > > +                     return -ENOMEM;
> >
> > Shouldn't we free files allocated on the previous iterations?
> 
> No, for the same reason explained in luo_session.c :-)

A comment here as well please :)

> > > +int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
> > > +                              struct file **filep)
> > > +{
> >
> > Ditto.
> 
> These two functions are part of the public API allowing dependency
> tracking for vfio->iommu->memfd during preservation.

So like with FLB, until we get actual users for them they are dead code. 
And until it's clear how exactly dependency tracking for vfio->iommu->memfd
will work, we won't know if this API is useful at all or we'll need
something else in the end.

-- 
Sincerely yours,
Mike.