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 16:48:14 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: Martin Kepplinger-Novakovic <martink@...teo.de>, Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>, <stable@...r.kernel.org>
CC: <patches@...ts.linux.dev>, ZhaoLong Wang <wangzhaolong1@...wei.com>,
	Richard Weinberger <richard@....at>, Miquel Raynal
	<miquel.raynal@...tlin.com>, Sasha Levin <sashal@...nel.org>,
	<linux-mtd@...ts.infradead.org>, <vigneshr@...com>,
	<dpervushin@...eddedalley.com>, <Artem.Bityutskiy@...ia.com>,
	<linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>,
	<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

在 2024/2/9 15:09, Martin Kepplinger-Novakovic 写道:
> Am Montag, dem 22.01.2024 um 15:56 -0800 schrieb Greg Kroah-Hartman:
>> 5.4-stable review patch.  If anyone has any objections, please let me
>> know.
>>
>> ------------------
>>
>> From: ZhaoLong Wang <wangzhaolong1@...wei.com>
>>
>> [ Upstream commit a43bdc376deab5fff1ceb93dca55bcab8dbdc1d6 ]
>>

[...]

>> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
>> index 0c05f77f9b21..dd0d0bf5f57f 100644
>> --- a/drivers/mtd/mtd_blkdevs.c
>> +++ b/drivers/mtd/mtd_blkdevs.c
>> @@ -533,7 +533,7 @@ static void blktrans_notify_add(struct mtd_info
>> *mtd)
>>   {
>>          struct mtd_blktrans_ops *tr;
>>   
>> -       if (mtd->type == MTD_ABSENT)
>> +       if (mtd->type == MTD_ABSENT || mtd->type == MTD_UBIVOLUME)
>>                  return;
>>   
>>          list_for_each_entry(tr, &blktrans_majors, list)
>> @@ -576,7 +576,7 @@ int register_mtd_blktrans(struct mtd_blktrans_ops
>> *tr)
>>          list_add(&tr->list, &blktrans_majors);
>>   
>>          mtd_for_each_device(mtd)
>> -               if (mtd->type != MTD_ABSENT)
>> +               if (mtd->type != MTD_ABSENT && mtd->type !=
>> MTD_UBIVOLUME)
>>                          tr->add_mtd(tr, mtd);
>>   
>>          mutex_unlock(&mtd_table_mutex);
> 
> 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