coredump: hold RCU while releasing parked threads

Overview

In the Linux kernel, the following vulnerability has been resolved:

coredump: hold RCU while releasing parked threads

coredump_finish() releases the parked threads by clearing ->task in their core_thread entry and calling wake_up_process() on each of them. It does that without holding a reference on the task and without being inside rcu.

But calling wake_up_process(task) without rcu here isn't safe. A parked thread doesn't need that wakeup to leave. A spurious wakeup or a preemption after the store is enough for the task to go away.

So if the coredump client is preempted between the store and wake_up_process() the thread can exit and be freed in the meantime and try_to_wake_up() takes pi_lock in freed memory.

Hold rcu across the loop.

Affected

• Linux >= a94e2d408eaedbd85aae259621d46fafc10479a2 < fd0fbe84312fda2fc187428c92c50b7d03a9d24c
• Linux >= a94e2d408eaedbd85aae259621d46fafc10479a2 < 71146c437bae59e5280f657965dc6d006ee3989b
• Linux >= a94e2d408eaedbd85aae259621d46fafc10479a2 < 0fce73efee40c65ce26641c5d93942462f9e8307
• Linux >= a94e2d408eaedbd85aae259621d46fafc10479a2 < 16e94ed90b1b02398e044d41fd1db34828daa08e
• Linux >= a94e2d408eaedbd85aae259621d46fafc10479a2 < a0f09ff4c6b93312e565cfe75d76c3a551a3ec4c
• Linux >= a94e2d408eaedbd85aae259621d46fafc10479a2 < b0eca0edddf4c1dbaf6d1f6a8636b4235f5bc573
• Linux >= a94e2d408eaedbd85aae259621d46fafc10479a2 < 61d58591aa0188bf2463e263962256316ff8b576
• Linux 2.6.27

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.