UBUNTU-CVE-2024-35985
In the Linux kernel, the following vulnerability has been resolved: sched/eevdf: Prevent vlag from going out of bounds in reweight_eevdf() It was possible to have pick_eevdf() return NULL, which then causes a NULL-deref. This turned out to be due to entity_eligible() returning falsely negative because of a s64 multiplcation overflow. Specifically, reweight_eevdf() computes the vlag without considering the limit placed upon vlag as update_entity_lag() does, and then the scaling multiplication (remember that weight is 20bit fixed point) can overflow. This then leads to the new vruntime being weird which then causes the above entity_eligible() to go side-ways and claim nothing is eligible. Thus limit the range of vlag accordingly. All this was quite rare, but fatal when it does happen.
02 / AFFECTED SOFTWARE
Affected packages
29 explicit affected versions
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26 explicit affected versions
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6 explicit affected versions
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16 explicit affected versions
43 explicit affected versions
9 explicit affected versions
2 explicit affected versions
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6 explicit affected versions
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50 explicit affected versions
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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: sched/eevdf: Prevent vlag from going out of bounds in reweight_eevdf() It was possible to have pick_eevdf() return NULL, which then causes a NULL-deref. This turned out to be due to entity_eligible() returning falsely negative because of a s64 multiplcation overflow. Specifically, reweight_eevdf() computes the vlag without considering the limit placed upon vlag as update_entity_lag() does, and then the scaling multiplication (remember that weight is 20bit fixed point) can overflow. This then leads to the new vruntime being weird which then causes the above entity_eligible() to go side-ways and claim nothing is eligible. Thus limit the range of vlag accordingly. All this was quite rare, but fatal when it does happen.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/1560d1f6eb6b398bddd80c16676776c0325fe5fe
- https://git.kernel.org/stable/c/06f27e6d7bf0abf54488259ef36bbf0e1fccb35c
- https://git.kernel.org/stable/c/1560d1f6eb6b398bddd80c16676776c0325fe5fe
- https://git.kernel.org/stable/c/470d347b14b0ecffa9b39cf8f644fa2351db3efb
- https://ubuntu.com/security/CVE-2024-35985
- https://ubuntu.com/security/notices/USN-6893-1
- https://ubuntu.com/security/notices/USN-6893-2
- https://ubuntu.com/security/notices/USN-6893-3
- https://ubuntu.com/security/notices/USN-6918-1
- https://www.cve.org/CVERecord?id=CVE-2024-35985