CVE-2024-47660

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.