CVE-2026-89985

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().