Re: [PATCH] mtd: require write permissions for locking and badblock ioctls

From: Michael Walle <michael@walle.cc>
To: Richard Weinberger <richard@nod.at>
Cc: linux-mtd <linux-mtd@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] mtd: require write permissions for locking and badblock ioctls
Date: Wed, 03 Mar 2021 17:25:48 +0100	[thread overview]
Message-ID: <040cf2058fe4cf5e63dbff534582881a@walle.cc> (raw)
In-Reply-To: <689194005.42755.1614788236355.JavaMail.zimbra@nod.at>

Am 2021-03-03 17:17, schrieb Richard Weinberger:
> Michael,
> 
> ----- Ursprüngliche Mail -----
>> Von: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
>> An: "Michael Walle" <michael@walle.cc>
>> CC: "linux-mtd" <linux-mtd@lists.infradead.org>, "linux-kernel" 
>> <linux-kernel@vger.kernel.org>, "Miquel Raynal"
>> <miquel.raynal@bootlin.com>, "richard" <richard@nod.at>, "Vignesh 
>> Raghavendra" <vigneshr@ti.com>
>> Gesendet: Mittwoch, 3. März 2021 17:08:56
>> Betreff: Re: [PATCH] mtd: require write permissions for locking and 
>> badblock ioctls
> 
>> On Wed, Mar 03, 2021 at 04:57:35PM +0100, Michael Walle wrote:
>>> MEMLOCK, MEMUNLOCK and OTPLOCK modify protection bits. Thus require
>>> write permission. Depending on the hardware MEMLOCK might even be
>>> write-once, e.g. for SPI-NOR flashes with their WP# tied to GND. 
>>> OTPLOCK
>>> is always write-once.
>>> 
>>> MEMSETBADBLOCK modifies the bad block table.
>>> 
>>> Fixes: f7e6b19bc764 ("mtd: properly check all write ioctls for 
>>> permissions")
>>> Signed-off-by: Michael Walle <michael@walle.cc>
>>> ---
>>>  drivers/mtd/mtdchar.c | 8 ++++----
>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>> 
>> Thanks for auditing the rest of these from my original patch.  If this
>> is ok with userspace tools, it's fine with me, but I don't even have
>> this hardware to test with :)
> 
> That's my fear. Michael, did you verify?

I don't know any tools except the mtd-utils. So no.

> In general you need to be root to open these device files.
> So, I don't see a security problem here.

Then this begs the question, why is this check there in
the first place?

This come up because I was adding a OTPERASE which
was suggested that is was a "dangerous" command. So I
was puzzled why the ones above are considered "safe" ;)

-michael