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In the Linux kernel, the following vulnerability has been resolved: pid_namespace: prevent TIF_NOTIFY_SIGNAL from interrupting the reaper Since commit 7fea700e04bd ("zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING") zap_pid_ns_processes() clears TIF_NOTIFY_SIGNAL before every kernel_wait4() call. Otherwise kernel_wait4() doesn't sleep and returns -ERESTARTSYS if signal_pending() is true and the reaper busy-waits. But clearing TIF_NOTIFY_SIGNAL doesn't fix it. It can get raised again. For example, klp_send_signals() sets it raw against any task that hasn't transitioned yet. And it keeps sending it until the livepatch finishes. The sleep loop waiting for pid_allocated to drop has the same problem and it doesn't even clear anything. So a schedule() in TASK_INTERRUPTIBLE returns immediately. Use a no_notify_signal guard. signal_pending() will ignore TIF_NOTIFY_SIGNAL and the pid namespace reaper sleeps until a child exits or free_pid() wakes it.

• https://git.kernel.org/stable/c/2c20ace1698d03a23467351be1d281e89b36ade3
• https://git.kernel.org/stable/c/9ab0324f4868eeb20c63f063a1e5bc01d5539212
• https://git.kernel.org/stable/c/30b274508c743f243c82904954c4e416d7143d4c
• https://git.kernel.org/stable/c/70178691c467c8f9f722765299fd8524c3121a35
• https://git.kernel.org/stable/c/3d15ac36ce174477efa5365e424dbd47950fd2b9
• https://git.kernel.org/stable/c/f46cd8241d9b83f2279cc0db3e9d3e181b548a59
• https://git.kernel.org/stable/c/5c0985dd3c32fc2bbd0e8beaf13cf52cd97376a2