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

From: Richard Weinberger <richard@nod.at>
To: chengzhihao1 <chengzhihao1@huawei.com>
Cc: Martin Kepplinger-Novakovic <martink@posteo.de>,
	 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	 stable <stable@vger.kernel.org>,
	patches@lists.linux.dev,
	 ZhaoLong Wang <wangzhaolong1@huawei.com>,
	 Miquel Raynal <miquel.raynal@bootlin.com>,
	 Sasha Levin <sashal@kernel.org>,
	 linux-mtd <linux-mtd@lists.infradead.org>,
	 Vignesh Raghavendra <vigneshr@ti.com>,
	 dpervushin <dpervushin@embeddedalley.com>,
	 Artem Bityutskiy <Artem.Bityutskiy@nokia.com>,
	 linux-kernel <linux-kernel@vger.kernel.org>,
	 yi zhang <yi.zhang@huawei.com>, yangerkun <yangerkun@huawei.com>,
	 Henri Roosen <Henri.Roosen@ginzinger.com>,
	 Melchior Franz <Melchior.Franz@ginzinger.com>
Subject: Re: [PATCH 5.4 058/194] mtd: Fix gluebi NULL pointer dereference caused by ftl notifier
Date: Sun, 18 Feb 2024 11:25:55 +0100 (CET)	[thread overview]
Message-ID: <1171523562.70108.1708251955853.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <a53aacd3-4270-2d80-f14c-8cfd763e4404@huawei.com>

----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1@huawei.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

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