Re: BUG: divide error in ubi_attach_mtd_dev

From: Lee Jones <lee@kernel.org>
To: Zhihao Cheng <chengzhihao1@huawei.com>
Cc: Richard Weinberger <richard@nod.at>, Yu Hao <yhao016@ucr.edu>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: BUG: divide error in ubi_attach_mtd_dev
Date: Mon, 2 Oct 2023 11:11:17 +0100	[thread overview]
Message-ID: <20231002101117.GA175828@google.com> (raw)
In-Reply-To: <951e4cf7-a0ea-b3ec-931d-e6a394ddc2ab@huawei.com>

On Sun, 23 Apr 2023, Zhihao Cheng wrote:

> 在 2023/4/23 16:02, Richard Weinberger 写道:
> > ----- Ursprüngliche Mail -----
> > > Von: "chengzhihao1" <chengzhihao1@huawei.com>
> > > > > root@syzkaller:~# cat /proc/mtd
> > > > > dev:    size   erasesize  name
> > > > > mtd0: 00020000 00001000 “mtdram test device”
> > > > 
> > > > Hmm, mtdram should be fine, erasesize is not zero.
> > > > 
> > > 
> > > I guess the zero-erasesize mtd device is dynamically generated in
> > > runtime, after looking through the code, I find erasesize is
> > > initiallized in specific flash driver and it won't be updated later(eg.
> > > ioctl\sysctl). And some mtd devices may have zero erasesize, eg.
> > > drivers/mtd/devices/mchp23k256.c[1]. Unfortunately, I don't know how to
> > > load/simulate this mtd, maybe it requires a real device? If we load this
> > > mtd device as ubi, it will trigger the problem?
> > 
> > Indeed. I guess qemu can emulate such chips.
> > So better fix UBI to reject attaching of mtd's with erasesize being 0.
> > (Please note, we cannot test for MTD_NO_ERASE, this one means there is no
> > erase method).
> 
> Phram is an exception, it has erase function but is set flag 'MTD_CAP_RAM'.
> May I interpret 'MTD_NO_ERASE' as erase function is not necessary?

For better or worse, someone has applied to have this report associated
with a CVE which means a bunch of companies and individuals are going to
be tracking it.

What is the current status please?

Is this deemed to be a real issue?

Did the report culminate in a posted patch?

Any help would be gratefully received.

-- 
Lee Jones [李琼斯]

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