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Re: How to secure access to SD cards a la USBGuard?

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On Fri 10 Dec 2021 at 17:20:52 (+0100), Andrei POPESCU wrote:
> On Lu, 06 dec 21, 10:18:49, David Wright wrote:
> > On Sun 05 Dec 2021 at 13:33:41 (+0100), Andrei POPESCU wrote:
> > > On Vi, 12 nov 21, 12:27:59, Stefan Monnier wrote:
> > > > 
> > > > As mentioned, the way to control it will depend on the specific tool
> > > > used to mount.  E.g. if it's mounted by hand via a rule in /etc/fstab,
> > > > then you can rules that specify the device via /etc/disk/by-uuid.
> > > > 
> > > > Do note that partition UUIDs are not designed to be reliable w.r.t
> > > > malicious uses (it's easy to create a partition with the same UUID as
> > > > some other).
> > > 
> > > /dev/disk/by-id/ should be device specific.
> > 
> > It certainly is, but specific to the card reader reading it,
> > not the card. And that's whether the card is plugged into a
> > slot on the computer, or into a discrete SD/USB adapter.
> 
> At least with the built-in reader on an Acer Chromebook R13 the ID 
> changes with every card I tested, but you are indeed right about USB 
> adapters (at least for the two I could test).

I did some comparisons between machines, and it would appear that
when the link starts with /dev/disk/by-id/mmc- then the ID is
that of the card, whereas when it starts with /dev/disk/by-id/usb-
then the ID is that of the card reader. Note that I did all the
comparisons using fullsize SD cards pushed into slots in the PCs,
so there were no separate adapters involved, neither SD→USB, nor µSD→SD.

As one might expect, googling mmc and usb is swamped with stuff about
MMC and SD /cards/, so I haven't read anything about the differences
between these slots on different computers. But I guess that if you
want to distinguish SD cards by their identification/serial number,
rather than strings that you write onto them (UUID/LABEL), you need
to use a PC with an mmc-style slot.

Cheers,
David.

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How to secure access to SD cards a la USBGuard? "hdv@gmail" <hdv.jadev@gmail.com> - 2021-11-11 18:50 +0100
  Re: How to secure access to SD cards a la USBGuard? Stefan Monnier <monnier@iro.umontreal.ca> - 2021-11-12 17:20 +0100
    Re: How to secure access to SD cards a la USBGuard? "hdv@gmail" <hdv.jadev@gmail.com> - 2021-11-12 18:10 +0100
      Re: How to secure access to SD cards a la USBGuard? Stefan Monnier <monnier@iro.umontreal.ca> - 2021-11-12 18:30 +0100
        Re: How to secure access to SD cards a la USBGuard? Andrei POPESCU <andreimpopescu@gmail.com> - 2021-12-05 13:40 +0100
          Re: How to secure access to SD cards a la USBGuard? "hdv@gmail" <hdv.jadev@gmail.com> - 2021-12-05 14:20 +0100
            Re: How to secure access to SD cards a la USBGuard? David Wright <deblis@lionunicorn.co.uk> - 2021-12-06 17:20 +0100
          Re: How to secure access to SD cards a la USBGuard? David Wright <deblis@lionunicorn.co.uk> - 2021-12-06 17:20 +0100
            Re: How to secure access to SD cards a la USBGuard? Andrei POPESCU <andreimpopescu@gmail.com> - 2021-12-10 17:30 +0100
              Re: How to secure access to SD cards a la USBGuard? David Wright <deblis@lionunicorn.co.uk> - 2022-01-03 04:00 +0100
                Re: How to secure access to SD cards a la USBGuard? Andrei POPESCU <andreimpopescu@gmail.com> - 2022-01-11 12:50 +0100
                Re: How to secure access to SD cards a la USBGuard? "hdv@gmail" <hdv.jadev@gmail.com> - 2022-01-11 17:50 +0100

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