Re: [dm-crypt] Recover from Spontaneous Ejection

[Arno Wagner <arno@wagner.name>]

You may run into the issue where that SD cards (like SSDs) may
actually use larger block-sizes than exposed at the interface.
Hence interrupting a write may damage parts that were not 
requested to be written.

SSDs have that mostly under control now, I think, probably by
adding some more complex commit schemes. But SD cards have 
far less comuting power and may not do that.

Regards,
Arno



On Wed, Jan 20, 2021 at 12:06:24 CET, Frederick Gotham wrote:
> 
>    I'm developing a product running embedded Linux.
> 
>    We have an SDcard with one partition on it, and this partition is an
>    encrypted LUKS volume.
> 
>    While the SDcard is mounted, the user can spontaneously eject the
>    SDcard. I have successfully altered the UDEV script to handle this
>    eventuality, as follows:
> 
>        umount /mnt/sdcard
>        cryptsetup luksClose cryptocard
> 
>    Then when the user re-inserts the SDcard after a spontaneous ejection,
>    I try to re-mount it again. So the entire process from start to finish
>    goes as follows:
> 
>        echo -n password | cryptsetup luksOpen /dev/sdb1 cryptocard -
>        mount /dev/mapper/cryptocard /mnt/sdcard
>        [ User spontaneously ejects SDcard  ]
>        umount /mnt/sdcard
>        cryptsetup luksClose cryptocard
>        [ ... ... ... 1 minute goes by ... ... ... ]
>        [         User re-inserts SD card         ]
>        echo -n password | cryptsetup luksOpen /dev/sdb1 cryptocard -
>        mount /dev/mapper/cryptocard /mnt/sdcard
> 
>    This appears to work just fine, however when I try to do more complex
>    write operations, it starts to freak out a little (files that were
>    previously visible are no longer visible). When I reboot the machine,
>    everything's working fine again.
> 
>    So it seems that the system is not adequately recovering from the
>    spontaneous ejection of the SDcard. Do I need to somehow "flush out"
>    the LUKS system in order to successfully re-mount the volume? Is it
>    possible to 'restart' the LUKS subsystem to get this to work properly
>    again? I only ever have one LUKS volume open at a time so I don't have
>    to worry about closing other volumes before 'flushing out'.
> 
>    Frederick

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-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
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