CVSS3
Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
AI Score
Confidence
Low
In the Linux kernel, the following vulnerability has been resolved:
Revert “sched/fair: Make sure to try to detach at least one movable task”
This reverts commit b0defa7ae03ecf91b8bfd10ede430cff12fcbd06.
b0defa7ae03ec changed the load balancing logic to ignore env.max_loop if
all tasks examined to that point were pinned. The goal of the patch was
to make it more likely to be able to detach a task buried in a long list
of pinned tasks. However, this has the unfortunate side effect of
creating an O(n) iteration in detach_tasks(), as we now must fully
iterate every task on a cpu if all or most are pinned. Since this load
balance code is done with rq lock held, and often in softirq context, it
is very easy to trigger hard lockups. We observed such hard lockups with
a user who affined O(10k) threads to a single cpu.
When I discussed this with Vincent he initially suggested that we keep
the limit on the number of tasks to detach, but increase the number of
tasks we can search. However, after some back and forth on the mailing
list, he recommended we instead revert the original patch, as it seems
likely no one was actually getting hit by the original issue.
git.kernel.org/stable/c/0fa6dcbfa2e2b97c1e6febbea561badf0931a38b
git.kernel.org/stable/c/1e116c18e32b035a2d1bd460800072c8bf96bc44
git.kernel.org/stable/c/2feab2492deb2f14f9675dd6388e9e2bf669c27a
git.kernel.org/stable/c/d467194018dd536fe6c65a2fd3aedfcdb1424903
security-tracker.debian.org/tracker/CVE-2024-42245