CVE-2025-39736 — mm/kmemleak: avoid deadlock by moving pr_warn() outside kmemleak_lock

Affected: Linux, Siemens SIMATIC CN 4100

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

mm/kmemleak: avoid deadlock by moving pr_warn() outside kmemleak_lock

When netpoll is enabled, calling pr_warn_once() while holding kmemleak_lock in mem_pool_alloc() can cause a deadlock due to lock inversion with the netconsole subsystem. This occurs because pr_warn_once() may trigger netpoll, which eventually leads to __alloc_skb() and back into kmemleak code, attempting to reacquire kmemleak_lock.

This is the path for the deadlock.

mem_pool_alloc() -> raw_spin_lock_irqsave(&kmemleak_lock, flags); -> pr_warn_once() -> netconsole subsystem -> netpoll -> __alloc_skb -> __create_object -> raw_spin_lock_irqsave(&kmemleak_lock, flags);

Fix this by setting a flag and issuing the pr_warn_once() after kmemleak_lock is released.

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CVE-2025-39736 — mm/kmemleak: avoid deadlock by moving pr_warn() outside kmemleak_lock