Status changed to 'Confirmed' because the bug affects multiple users.
** Changed in: chromium-browser (Ubuntu)
Status: New => Confirmed
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https://bugs.launchpad.net/bugs/1905458
Title:
[snap] Chromium USB enumeration fails when usbmon module is loaded
Status in chromium-browser package in Ubuntu:
Confirmed
Bug description:
Version:
chromium 87.0.4280.66 1411
Steps to reproduce:
1. Have Chromium snap, with raw-usb plug connected.
2. sudo modprobe usbmon.
3. Open Chromium and try to use a webpage that has webusb.
Result:
Chromium cannot see any USB devices on the system, regardless of
whether it has raw-usb or not.
The following errors are printed on dmesg:
```
[3701471.283584] audit: type=1400 audit(1606101844.664:6015):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:4" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283636] audit: type=1400 audit(1606101844.664:6016):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:2" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283700] audit: type=1400 audit(1606101844.664:6017):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:0" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283786] audit: type=1400 audit(1606101844.664:6018):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:7" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283869] audit: type=1400 audit(1606101844.664:6019):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:5" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283982] audit: type=1400 audit(1606101844.664:6020):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:3" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
```
Chromium will then print this on stderr:
```
[3121487:3121626:1123/032552.888385:ERROR:udev_watcher.cc(97)] Failed to
begin udev enumeration.
```
Why this happens:
Chromium enumerates USB devices by querying udev. Specifically by
using udev_enumerate_scan_devices. When usbmon module is loaded, some
new device nodes are created for the monitor endpoints. They are only
readable by root. When Chromium scans for normal USB devices, it finds
the monitors and tries to probe them. Apparmor blocks it, which causes
udev_enumerate_scan_devices to fail.
Impact:
There is no way for the user to know this error has occurred unless
they happen to be watching dmesg or the stderr of Chromium (which
requires they ran it from a terminal). Unless they check both of these
places and realize that the error messages are connected, Chromium
will just appear to behave as if there are no USB devices connected to
the system at all. If the user does realize that usbmon is causing a
problem, they must restart Chromium after unloading it, because it
will not retry if enumeration ever fails.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/chromium-browser/+bug/1905458/+subscriptions
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