UBUNTU-CVE-2024-42245
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.
02 / AFFECTED SOFTWARE
Affected packages
9 explicit affected versions
15 explicit affected versions
29 explicit affected versions
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11 explicit affected versions
1 explicit affected versions
15 explicit affected versions
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7 explicit affected versions
26 explicit affected versions
37 explicit affected versions
10 explicit affected versions
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7 explicit affected versions
37 explicit affected versions
8 explicit affected versions
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23 explicit affected versions
7 explicit affected versions
10 explicit affected versions
1 explicit affected versions
33 explicit affected versions
15 explicit affected versions
12 explicit affected versions
16 explicit affected versions
13 explicit affected versions
12 explicit affected versions
12 explicit affected versions
38 explicit affected versions
51 explicit affected versions
13 explicit affected versions
10 explicit affected versions
10 explicit affected versions
13 explicit affected versions
12 explicit affected versions
1 explicit affected versions
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5 explicit affected versions
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10 explicit affected versions
13 explicit affected versions
21 explicit affected versions
6 explicit affected versions
13 explicit affected versions
12 explicit affected versions
11 explicit affected versions
14 explicit affected versions
7 explicit affected versions
14 explicit affected versions
6 explicit affected versions
8 explicit affected versions
12 explicit affected versions
26 explicit affected versions
7 explicit affected versions
23 explicit affected versions
14 explicit affected versions
5 explicit affected versions
3 explicit affected versions
26 explicit affected versions
12 explicit affected versions
44 explicit affected versions
4 explicit affected versions
4 explicit affected versions
16 explicit affected versions
9 explicit affected versions
12 explicit affected versions
13 explicit affected versions
7 explicit affected versions
6 explicit affected versions
13 explicit affected versions
7 explicit affected versions
10 explicit affected versions
14 explicit affected versions
18 explicit affected versions
3 explicit affected versions
16 explicit affected versions
43 explicit affected versions
14 explicit affected versions
5 explicit affected versions
7 explicit affected versions
11 explicit affected versions
35 explicit affected versions
12 explicit affected versions
13 explicit affected versions
6 explicit affected versions
12 explicit affected versions
50 explicit affected versions
14 explicit affected versions
11 explicit affected versions
12 explicit affected versions
27 explicit affected versions
12 explicit affected versions
7 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/2feab2492deb2f14f9675dd6388e9e2bf669c27a
- https://git.kernel.org/stable/c/0fa6dcbfa2e2b97c1e6febbea561badf0931a38b
- https://git.kernel.org/stable/c/1e116c18e32b035a2d1bd460800072c8bf96bc44
- https://git.kernel.org/stable/c/2feab2492deb2f14f9675dd6388e9e2bf669c27a
- https://git.kernel.org/stable/c/d467194018dd536fe6c65a2fd3aedfcdb1424903
- https://ubuntu.com/security/CVE-2024-42245
- https://ubuntu.com/security/notices/USN-7089-1
- https://ubuntu.com/security/notices/USN-7089-2
- https://ubuntu.com/security/notices/USN-7089-3
- https://ubuntu.com/security/notices/USN-7089-4
- https://ubuntu.com/security/notices/USN-7089-5
- https://ubuntu.com/security/notices/USN-7089-6
- https://ubuntu.com/security/notices/USN-7089-7
- https://ubuntu.com/security/notices/USN-7090-1
- https://ubuntu.com/security/notices/USN-7095-1
- https://ubuntu.com/security/notices/USN-7156-1
- https://www.cve.org/CVERecord?id=CVE-2024-42245