CVE-2026-64418

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.

Weakness

The product contains a concurrent code sequence that 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 operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

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