Debian ISOs on USB stick, was: SOLVED

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

David Christensen wrote:
> It's a relatively simple experiment to confirm that a USB flash drive with
> d-i changes after the first boot.

This could still be
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1056998
where Lenovo BIOS and/or MS-Windows altered the USB stick.


> Same for finding which bytes change.

I fail to find this particular info in
  Date: Tue, 2 Apr 2024 14:46:42 -0700
  From: David Christensen <dpchrist@holgerdanske.com>
  Message-ID: <[🔎] fbeae732-04c7-457d-911b-4686c2466ebd@holgerdanske.com>

If we have the exact ISO name (i.e. URL from where it stems) and the
byte address of the alteration, xorriso can find the affected file, if
any.

In case of bug #1056998 it was the EFI partition image /boot/grub/efi.img.
Mounting the altered and unaltered image files showed changes in the
FAT filesystem which point to the culprits Lenovo and Microsoft.


The other plausible way of altering the ISO image on the stick would be
adding a new partition.
The MBR partition table is part of the Debian ISO and thus part of the
checksummed area. Even if all other alterations happen after the end
of the checksummed ISO image, the changed partition table will cause the
Debian checksum to become invalid.

(I am not aware that Debian installer changes the table. If it does indeed
then this might be worth a new bug discussion.)


Have a nice day :)

Thomas