Daan De Meyer
bce7b82268
The BPF kprobe that fires on user namespace destruction is the only thing that triggers registry cleanup, so any time it doesn't run — ring buffer overflow, kprobe missing, fdstore entry dropped outside our cleanup path — a registry entry is left behind forever. Stamp each registry entry with the kernel's unique namespace identifier (NS_GET_ID, kernel ≥ 6.13) at allocation time. At manager startup, after the existing fdstore→registry sweep, walk the registry and ask the kernel to look each namespace up by id via open_by_handle_at() on nsfs; if the lookup returns -ESTALE the namespace is gone and we release the entry. Old entries written before this change carry no identifier and are left alone. Add a namespace_open_by_id() helper for the lookup. The kernel restricts open_by_handle_at() on nsfs to processes in the initial user namespace, collapsing both permission denials and dead namespaces onto -ESTALE; the helper refuses early with -EPERM outside the initial user namespace so callers can tell the two apart.
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