CVE-2025-68780 (GCVE-0-2025-68780)

Vulnerability from cvelistv5 – Published: 2026-01-13 15:28 – Updated: 2026-05-11 21:53
VLAI
Title
sched/deadline: only set free_cpus for online runqueues
Summary
In the Linux kernel, the following vulnerability has been resolved: sched/deadline: only set free_cpus for online runqueues Commit 16b269436b72 ("sched/deadline: Modify cpudl::free_cpus to reflect rd->online") introduced the cpudl_set/clear_freecpu functions to allow the cpu_dl::free_cpus mask to be manipulated by the deadline scheduler class rq_on/offline callbacks so the mask would also reflect this state. Commit 9659e1eeee28 ("sched/deadline: Remove cpu_active_mask from cpudl_find()") removed the check of the cpu_active_mask to save some processing on the premise that the cpudl::free_cpus mask already reflected the runqueue online state. Unfortunately, there are cases where it is possible for the cpudl_clear function to set the free_cpus bit for a CPU when the deadline runqueue is offline. When this occurs while a CPU is connected to the default root domain the flag may retain the bad state after the CPU has been unplugged. Later, a different CPU that is transitioning through the default root domain may push a deadline task to the powered down CPU when cpudl_find sees its free_cpus bit is set. If this happens the task will not have the opportunity to run. One example is outlined here: https://lore.kernel.org/lkml/20250110233010.2339521-1-opendmb@gmail.com Another occurs when the last deadline task is migrated from a CPU that has an offlined runqueue. The dequeue_task member of the deadline scheduler class will eventually call cpudl_clear and set the free_cpus bit for the CPU. This commit modifies the cpudl_clear function to be aware of the online state of the deadline runqueue so that the free_cpus mask can be updated appropriately. It is no longer necessary to manage the mask outside of the cpudl_set/clear functions so the cpudl_set/clear_freecpu functions are removed. In addition, since the free_cpus mask is now only updated under the cpudl lock the code was changed to use the non-atomic __cpumask functions.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 9659e1eeee28f7025b6545934d644d19e9c6e603 , < 9019e399684e3cc68c4a3f050e268f74d69c1317 (git)
Affected: 9659e1eeee28f7025b6545934d644d19e9c6e603 , < fb36846cbcc936954f2ad2bffdff13d16c0be08a (git)
Affected: 9659e1eeee28f7025b6545934d644d19e9c6e603 , < 91e448e69aca4bb0ba2e998eb3e555644db7322b (git)
Affected: 9659e1eeee28f7025b6545934d644d19e9c6e603 , < dbc61834b0412435df21c71410562d933e4eba49 (git)
Affected: 9659e1eeee28f7025b6545934d644d19e9c6e603 , < 3ed049fbfb4d75b4e0b8ab54c934f485129d5dc8 (git)
Affected: 9659e1eeee28f7025b6545934d644d19e9c6e603 , < 382748c05e58a9f1935f5a653c352422375566ea (git)
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Linux Linux Affected: 4.0
Unaffected: 0 , < 4.0 (semver)
Unaffected: 5.15.198 , ≤ 5.15.* (semver)
Unaffected: 6.1.160 , ≤ 6.1.* (semver)
Unaffected: 6.6.120 , ≤ 6.6.* (semver)
Unaffected: 6.12.64 , ≤ 6.12.* (semver)
Unaffected: 6.18.3 , ≤ 6.18.* (semver)
Unaffected: 6.19 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched/deadline: only set free_cpus for online runqueues\n\nCommit 16b269436b72 (\"sched/deadline: Modify cpudl::free_cpus\nto reflect rd-\u003eonline\") introduced the cpudl_set/clear_freecpu\nfunctions to allow the cpu_dl::free_cpus mask to be manipulated\nby the deadline scheduler class rq_on/offline callbacks so the\nmask would also reflect this state.\n\nCommit 9659e1eeee28 (\"sched/deadline: Remove cpu_active_mask\nfrom cpudl_find()\") removed the check of the cpu_active_mask to\nsave some processing on the premise that the cpudl::free_cpus\nmask already reflected the runqueue online state.\n\nUnfortunately, there are cases where it is possible for the\ncpudl_clear function to set the free_cpus bit for a CPU when the\ndeadline runqueue is offline. When this occurs while a CPU is\nconnected to the default root domain the flag may retain the bad\nstate after the CPU has been unplugged. Later, a different CPU\nthat is transitioning through the default root domain may push a\ndeadline task to the powered down CPU when cpudl_find sees its\nfree_cpus bit is set. If this happens the task will not have the\nopportunity to run.\n\nOne example is outlined here:\nhttps://lore.kernel.org/lkml/20250110233010.2339521-1-opendmb@gmail.com\n\nAnother occurs when the last deadline task is migrated from a\nCPU that has an offlined runqueue. The dequeue_task member of\nthe deadline scheduler class will eventually call cpudl_clear\nand set the free_cpus bit for the CPU.\n\nThis commit modifies the cpudl_clear function to be aware of the\nonline state of the deadline runqueue so that the free_cpus mask\ncan be updated appropriately.\n\nIt is no longer necessary to manage the mask outside of the\ncpudl_set/clear functions so the cpudl_set/clear_freecpu\nfunctions are removed. In addition, since the free_cpus mask is\nnow only updated under the cpudl lock the code was changed to\nuse the non-atomic __cpumask functions."
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