linux-kernel - Re: [PATCH 5/5] ubi: Allow to use read-only UBI volume with not enough PEBs

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Message-ID: <0527d020-95aa-80e5-978c-fa9b6761a273@nod.at>
Date:   Sun, 6 Aug 2017 11:43:25 +0200
From:   Richard Weinberger <richard@....at>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Artem Bityutskiy <dedekind1@...il.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] ubi: Allow to use read-only UBI volume with not
 enough PEBs

Pali,

Am 25.07.2017 um 16:27 schrieb Pali Rohár:
>> I fear this is not correct, it will disable a legit self-check of UBI volumes.
>> If the read-only volume is corrupted/truncated and you miss PEBs, this
>> check will no longer
>> trigger.
>>
>> Especially when dealing with nanddumps, truncation is a common problem.
> 
> Any idea how to fix it? Or how to handle read-only images which are
> marked for auto-resize?

I'd vote for rejecting images that have auto-resize set when the MTD is read-only.
In fact, using UBI on top of a read-only MTD is very uncommon and not recommended (for NAND).
The auto-resize flag should be also only set when you just have created it using mkfs.ubifs.
Why would you inspect such an image with the kernel UBIFS unless you're hunting down a bug
in mkfs.ubifs?

Thanks,
//richard