CVE-2024-47660: fsnotify: clear PARENT_WATCHED flags lazily

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-10-09 · updated 2026-10-15
Weakness: CWE-362

Description

In the Linux kernel, the following vulnerability has been resolved: fsnotify: clear PARENT_WATCHED flags lazily In some setups directories can have many (usually negative) dentries. Hence __fsnotify_update_child_dentry_flags() function can take a significant amount of time. Since the bulk of this function happens under inode->i_lock this causes a significant contention on the lock when we remove the watch from the directory as the __fsnotify_update_child_dentry_flags() call from fsnotify_recalc_mask() races with __fsnotify_update_child_dentry_flags() calls from __fsnotify_parent() happening on children. This can lead upto softlockup reports reported by users. Fix the problem by calling fsnotify_update_children_dentry_flags() to set PARENT_WATCHED flags only when parent starts watching children. When parent stops watching children, clear false positive PARENT_WATCHED flags lazily in __fsnotify_parent() for each accessed child.

Affected products

Linux kernel: before 5.10.226; from 5.11 before 5.15.167; from 5.16 before 6.1.109; from 6.2 before 6.6.50; from 6.7 before 6.10.9 — fixed in 5.10.226, 5.15.167, 6.1.109, 6.10.9, 6.6.50

How to fix

Upgrade to a fixed version: Linux kernel 5.10.226, 5.15.167, 6.1.109, 6.10.9. Check the vendor advisory for mitigations.

References

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