Linux Kernel up to 7.2.4 memcg memcg_reparent_objcgs race condition

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2.4. It has been rated as very critical. The impacted element is the function memcg_reparent_objcgs of the component memcg. The manipulation leads to race condition. This vulnerability is uniquely identified as CVE-2026-89985. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.2.4 and classified as very critical. This issue affects the function memcg_reparent_objcgs of the component memcg. The manipulation with an unknown input leads to a race condition vulnerability. Using CWE to declare the problem leads to CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: memcg: keep folio's objcg same as its node memcg_reparent_objcgs() has an inherent assumption that a folio's objcg is the objcg of the folio's node. Folio migration across nodes breaks that assumption: the new folio simply inherits the old folio's objcg while living on a different node. Once the assumption is broken, the reparenting of the folio's objcg and the reparenting of the folio's LRU list are no longer atomic. memcg_reparent_objcgs() handles one node per iteration and drops all the locks in between, so the objcg gets reparented in the iteration for the objcg's node while the LRU list gets spliced in the iteration for the folio's node. Any LRU operation on that folio in between resolves its lruvec through the objcg, and thus takes the lru_lock of the wrong memcg, not the lru_lock of the list the folio is actually on. Fix this by selecting the objcg by folio_nid() at charge time, and by re-deriving it for the destination node in mem_cgroup_migrate() and mem_cgroup_replace_folio().

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2026-89985 since 09/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/16/2026).

Upgrading to version 7.2.5 or 7.3-rc1 eliminates this vulnerability. Applying the patch 6165478eaa3094eaee1d5e33b12520064faf043d/bf4ade7dbd76d4ec8697840e4ebb15ed77c5ec26 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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