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

[Michael Walle]

Am 2021-03-03 17:17, schrieb Richard Weinberger:
> Michael,
>
> ----- Ursprüngliche Mail -----
> > Von: "Greg Kroah-Hartman" <gregkh@xxxxxxxxxxxxxxxxxxx>
> > An: "Michael Walle" <michael@xxxxxxxx>
> > CC: "linux-mtd" <linux-mtd@xxxxxxxxxxxxxxxxxxx>, "linux-kernel" 
> > <linux-kernel@xxxxxxxxxxxxxxx>, "Miquel Raynal"
> > <miquel.raynal@xxxxxxxxxxx>, "richard" <richard@xxxxxx>, "Vignesh 
> > Raghavendra" <vigneshr@xxxxxx>
> > 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@xxxxxxxx>
> > > ---
> > >  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