CVE-2026-64419
Low risk· EPSS 7%Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
In the Linux kernel, the shrinker mechanism has a bug where RCU lock is held while calling the ->count_objects() callback in shrinker_debugfs_count_show(). The zswap_shrinker_count() function may sleep via css_rstat_flush(), which is not allowed in an RCU critical section. The fix removes rcu_read_lock()/rcu_read_unlock(), as they are unnecessary.
Risk Assessment
The organization may experience critical errors or system hangs when reading the shrinker debugfs file, especially with zswap, which can hinder diagnostics.
Recommendation
It is recommended to update the Linux kernel to a version containing the fix for CVE-2026-64419 to avoid synchronization issues in shrinker debugfs.
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Original NVD description (English source)
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().