** Also affects: linux-oem (Ubuntu)
Importance: Undecided
Status: New
** No longer affects: linux-oem (Ubuntu Xenial)
** No longer affects: linux-oem (Ubuntu Disco)
** No longer affects: linux-oem (Ubuntu Eoan)
** No longer affects: linux-oem (Ubuntu Focal)
** Changed in: linux-oem (Ubuntu Bionic)
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/1861238
Title:
Root can lift kernel lockdown via USB/IP
Status in linux package in Ubuntu:
In Progress
Status in linux-oem package in Ubuntu:
New
Status in linux source package in Xenial:
Invalid
Status in linux source package in Bionic:
Fix Committed
Status in linux-oem source package in Bionic:
Fix Committed
Status in linux source package in Disco:
Fix Committed
Status in linux source package in Eoan:
Fix Committed
Status in linux source package in Focal:
In Progress
Bug description:
[Impact]
It's possible to turn off kernel lockdown by emulating a USB keyboard
via USB/IP and sending an Alt+SysRq+X key combination through it.
Ubuntu's kernels have USB/IP enabled (CONFIG_USBIP_VHCI_HCD=m and
CONFIG_USBIP_CORE=m) with signed usbip_core and vhci_hcd modules
provided in the linux-extra-modules-* package.
See the PoC here: https://github.com/xairy/unlockdown#method-1-usbip
[Test Case]
$ git clone https://github.com/xairy/unlockdown.git
$ cd unlockdown/01-usbip/
$ sudo ./run.sh
$ dmesg
# Ensure there are no log entries talking about lifting lockdown:
sysrq: SysRq : Disabling Secure Boot restrictions
Lifting lockdown
# You should see a SysRq help log entry because the Alt+SysRq+X
# combination should be disabled
sysrq: SysRq : HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e)
memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k)
show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n)
poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s)
show-task-states(t) unmount(u) force-fb(V) show-blocked-tasks(w)
dump-ftrace-buffer(z)
[Regression Potential]
Some users may see a usability regression due to the Lockdown lift
sysrq combination being removed. Some users are known to disable
lockdown, using the sysrq combination, in order to perform some
"dangerous" operation such as writing to an MSR. It is believed that
this is a small number of users but it is impossible to know for sure.
Users that rely on this functionality may need to permanently disable
secure boot using 'mokutil --disable-validation'.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1861238/+subscriptions
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