CVE-2026-64418

Summary

In the Linux kernel, the following vulnerability has been resolved:

mm: shrinker: fix shrinker_info teardown race with expansion

expand_shrinker_info() iterates all visible memcgs under shrinker_mutex, including memcgs that have not finished ->css_online() yet.

Once pn->shrinker_info has been published, teardown must stay serialized with expand_shrinker_info() until that memcg is either fully online or no longer visible to iteration. Today alloc_shrinker_info() breaks that rule by dropping shrinker_mutex before freeing a partially initialized shrinker_info array, which may cause the following race:

CPU0 CPU1 ==== ====

css_create –> list_add_tail_rcu(&css->sibling, &parent_css->children); online_css –> mem_cgroup_css_online –> alloc_shrinker_info –> alloc node0 info rcu_assign_pointer(C->node0->shrinker_info, old0) alloc node1 info -> FAIL -> goto err mutex_unlock(shrinker_mutex)

                   shrinker_alloc()
                   --> shrinker_memcg_alloc
                       --> mutex_lock(shrinker_mutex)
                           expand_shrinker_info
                           --> mem_cgroup_iter see the memcg
                               expand_one_shrinker_info
                               --> old0 = C->node0->shrinker_info
                                   memcpy(new->unit, old0->unit, ...);

            free_shrinker_info
            --> kvfree(old0);

                                   /* double free !! */
                                   kvfree_rcu(old0, rcu);

The same problem exists later in mem_cgroup_css_online(). If alloc_shrinker_info() succeeds but a subsequent objcg allocation fails, the free_objcg -> free_shrinker_info() unwind path tears down the already published pn->shrinker_info arrays without shrinker_mutex. The expand_one_shrinker_info() can race with that teardown in the same way, leading to use-after-free or double-free of the old shrinker_info.

Fix this by serializing shrinker_info teardown with shrinker_mutex, and by keeping alloc_shrinker_info() error cleanup inside the locked section.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/b9a280a9a454ed514636351d53fe2a233dc5054b
• https://git.kernel.org/stable/c/6465ff3ce65131c774a312d450abe10f4b9f3875
• https://git.kernel.org/stable/c/284c267f013e45d8c89d9fb9373105dc8e6c0947
• https://git.kernel.org/stable/c/65476d31d8056e859c48580f82295ce159196ffe

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