CVE-2026-64419 mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show()

What is CVE-2026-64419?

CVE-2026-64419 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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

mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show()

Reading the debugfs "count" file of a memcg-aware shrinker can sleep inside an RCU read-side critical section:

BUG: sleeping function called from invalid context at kernel/cgroup/rstat.c:421 RCU nest depth: 1, expected: 0 css_rstat_flush mem_cgroup_flush_stats zswap_shrinker_count shrinker_debugfs_count_show

shrinker_debugfs_count_show() invokes the ->count_objects() callback under rcu_read_lock(). The zswap callback flushes memcg stats via css_rstat_flush(), which may sleep, so it must not run under RCU.

The RCU lock is not needed here. mem_cgroup_iter() takes RCU internally and returns a memcg holding a css reference (dropped on the next iteration or by mem_cgroup_iter_break()), so the memcg stays alive without it. The shrinker is kept alive by the open debugfs file: shrinker_free() removes the debugfs entries via debugfs_remove_recursive(), which waits for in-flight readers to drain, before call_rcu(..., shrinker_free_rcu_cb). The sibling "scan" handler already invokes the sleeping ->scan_objects() callback with no RCU section.

Drop the rcu_read_lock()/rcu_read_unlock().

Which versions are affected by CVE-2026-64419?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-64419?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-64419 being exploited?

There is no known exploitation of CVE-2026-64419 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2026-64419, DEBIAN-CVE-2026-64419, GHSA-h85j-5g9p-ppj5, ROOT-OS-UBUNTU-2204-CVE-2026-64419, UBUNTU-CVE-2026-64419.