linux-kernel - Re: [PATCH 5.4 058/194] mtd: Fix gluebi NULL pointer dereference caused by ftl notifier

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Date: Sun, 18 Feb 2024 11:25:55 +0100 (CET)
From: Richard Weinberger <richard@....at>
To: chengzhihao1 <chengzhihao1@...wei.com>
Cc: Martin Kepplinger-Novakovic <martink@...teo.de>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	stable <stable@...r.kernel.org>, patches@...ts.linux.dev, 
	ZhaoLong Wang <wangzhaolong1@...wei.com>, 
	Miquel Raynal <miquel.raynal@...tlin.com>, 
	Sasha Levin <sashal@...nel.org>, 
	linux-mtd <linux-mtd@...ts.infradead.org>, 
	Vignesh Raghavendra <vigneshr@...com>, 
	dpervushin <dpervushin@...eddedalley.com>, 
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>, 
	linux-kernel <linux-kernel@...r.kernel.org>, 
	yi zhang <yi.zhang@...wei.com>, yangerkun <yangerkun@...wei.com>, 
	Henri Roosen <Henri.Roosen@...zinger.com>, 
	Melchior Franz <Melchior.Franz@...zinger.com>
Subject: Re: [PATCH 5.4 058/194] mtd: Fix gluebi NULL pointer dereference
 caused by ftl notifier

----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1@...wei.com>
>> Hi Greg, hi patch-developers,
>> 
>> wait a second. this already went into v5.4.268 but still: Doesn't this
>> break userspace?
>> 
>> According to
>> https://lore.kernel.org/lkml/441107100.23734.1697904580252.JavaMail.zimbra@nod.at/
>> where this solution seems to come from, the behaviour changes: "no
>> mtdblock (hence, also no FTLs) on top of gluebi."
>> 
>> I fell accross this because of an out-of-tree module that does
>> sys_mount() an mtdblock, so I won't complain about my code specifically
>> :) But doesn't it break mounting, say, jffs2 inside an ubi via
>> mtdblock? If so, is this really something that you want to see
>> backported to old kernels?
>> 
>> Or differently put: Has this patch been picked up for old stable
>> kernels by scripts or by a human?
>> 
>> I just want to make sure, and who knows, it might help others too, who
>> would just do a (possibly dangerous?) revert in their trees.
>> 
> 
> This change does affect the mounting(mtdblock based on gluebi) behavior
> in userspace. It was picked into stable versions because the fixed
> problem is serious and easy to be reproduced, I guess.
> A temporary solution is that modify mounting source target in userspace,
> just replace mtdblock with mtd char device. For example, mount -t jffs2
> mtd0 /mnt

I don't think this needs backporting to stable. It's not serious because you
still need to be root to setup and trigger such a scenario.

Thanks,
//richard