[Bug 1863239] Re: /dev/bus/usb/*/* device file of HP multi-function printer assigned to "audio" group

[Till Kamppeter]

There was already a measure against wrongly identifying HP printers as
media players, but it is a rather dirty workaround which does not work
any more (therefore this bug). The rule in the end of 69-libmtp.rules
checks the absence of the env variable libsane_matched and this variable
is set for all HP printers by HPLIP. First, this rule fails miserably if
HPLIP is not installed, and I cannot imagine that the libmtp package
depends on HPLIP only to identify unsupported devices. Also the libmtp
rules are applied for both "add" and "bind" actions, whereas the rules
of HPLIP (56-hpmud.rules) are only applied for "add" and so the bug
happens on a "bind" action, here the HPLIP rules do not set said env
variable and so the libmtp rules probe the HP printers.

One can theoretically work around this problem by mucking with the UDEV
rules of HPLIP, but this is a REALLY DIRTY workaround, so please DO NOT
add an hplip task to this bug report.

In addition, HPLIP will not be installed by default any more in the not
too far future, as prnting and scanning will get snapped. Also we want
printer driver Snaps (Printer Applications) not to run as root if
possible, so we need to be sure that USB printer device files always
belong to the group "lp" for all printer manufacturers and without
HPLIP.

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https://bugs.launchpad.net/bugs/1863239

Title:
  /dev/bus/usb/*/* device file of HP multi-function printer assigned to
  "audio" group

Status in libmtp package in Ubuntu:
  Confirmed
Status in pulseaudio package in Ubuntu:
  Invalid
Status in systemd package in Ubuntu:
  Invalid
Status in udev package in Ubuntu:
  Invalid

Bug description:
  When testing HPLIP I found out that CUPS backends can access my
  printer only when they are running as root, when they are running as
  the special user lp, as it is usually the case, they cannot access the
  printer.

  So I tried to find out why and saw that the /dev/bus/usb/*/* device
  file for the printer has group ownership "audio" and not "lp":

  till at till-x1yoga:~/ubuntu/hplip/focal/debian/hplip-3.19.12+dfsg0$ ll /dev/bus/usb/*/*
  crw-rw-r--  1 root root    189,   0 Feb 11 14:17 /dev/bus/usb/001/001
  crw-rw-r--  1 root root    189,   2 Feb 11 14:17 /dev/bus/usb/001/003
  crw-rw-r--  1 root root    189,   3 Feb 11 14:17 /dev/bus/usb/001/004
  crw-rw-r--  1 root plugdev 189,   4 Feb 14 12:23 /dev/bus/usb/001/005
  crw-rw-r--  1 root root    189,   5 Feb 11 14:17 /dev/bus/usb/001/006
  crw-rw----+ 1 root audio   189,  62 Feb 14 12:37 /dev/bus/usb/001/063
  crw-rw-r--  1 root root    189, 128 Feb 11 14:17 /dev/bus/usb/002/001
  crw-rw-r--  1 root root    189, 130 Feb 13 09:38 /dev/bus/usb/002/003
  till at till-x1yoga:~/ubuntu/hplip/focal/debian/hplip-3.19.12+dfsg0$

  The printer is the device /dev/bus/usb/001/063:

  till at till-x1yoga:~/ubuntu/hplip/focal/debian/hplip-3.19.12+dfsg0$ lsusb
  Bus 002 Device 003: ID 0b95:1790 ASIX Electronics Corp. AX88179 Gigabit Ethernet
  Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
  Bus 001 Device 005: ID 138a:0097 Validity Sensors, Inc. 
  Bus 001 Device 004: ID 04f2:b5ce Chicony Electronics Co., Ltd Integrated Camera
  Bus 001 Device 003: ID 8087:0a2b Intel Corp. 
  Bus 001 Device 006: ID 056a:50b7 Wacom Co., Ltd Pen and multitouch sensor
  Bus 001 Device 063: ID 03f0:7a12 HP, Inc HP OfficeJet Pro 8730
  Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
  till at till-x1yoga:~/ubuntu/hplip/focal/debian/hplip-3.19.12+dfsg0$ 

  There must be a bug somewhere in the UDEV rules.

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