High [CVE-2026-72069] Fix the incorrect RCU protection in rt_spin_unlock

In the Linux kernel, the following vulnerability has been resolved: locking/rt: Fix the incorrect RCU protection in rt_spin_unlock() rt_spin_unlock() releases the RCU protection before unlocking the lock.

That opens the door for the following UAF scenario: T1T2 spin_lock(&p->lock);rcu_read_lock(); invalidate(p);p = rcu_dereference(ptr); rcu_assign_pointer(ptr, NULL);if (!p) return; spin_unlock(&p->lock);spin_lock(&p->lock) lock(&lock->lock); rcu_read_lock(); kfree_rcu(p);rcu_read_unlock();.... spin_unlock(&p->lock) rcu_read_unlock(); // Ends grace period rcu_do_batch() kfree(p); UAF -> rt_mutex_cmpxchg_release(&lock->lock...) Regular spinlocks keep preemption disabled accross the unlock operation, which provides full RCU protection, but the RT substitution fails to resemble that.

Same applies for the rwlock substitution. Move the rcu_read_unlock() invocation past the unlock operations to match the non-RT semantics.

This makes it asymmetric vs. rt_xxx_lock(), but that's harmless as the caller needs to hold RCU read lock across the lock operation. The migrate_enable() call stays before the unlock operation because there is no per CPU operation in the unlock path which would require migration to be kept disabled.

Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9; Red Hat package: kernel-rt.