binder: fix node UAF in binder_add_freeze_work()

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

binder: fix node UAF in binder_add_freeze_work()

In binder_add_freeze_work() we iterate over the proc->nodes with the

proc->inner_lock held. However, this lock is temporarily dropped in

order to acquire the node->lock first (lock nesting order). This can

race with binder_node_release() and trigger a use-after-free:

==================================================================

BUG: KASAN: slab-use-after-free in _raw_spin_lock+0xe4/0x19c

Write of size 4 at addr ffff53c04c29dd04 by task freeze/640

CPU: 5 UID: 0 PID: 640 Comm: freeze Not tainted 6.11.0-07343-ga727812a8d45 #17

Hardware name: linux,dummy-virt (DT)

Call trace:

_raw_spin_lock+0xe4/0x19c

binder_add_freeze_work+0x148/0x478

binder_ioctl+0x1e70/0x25ac

__arm64_sys_ioctl+0x124/0x190

Allocated by task 637:

__kmalloc_cache_noprof+0x12c/0x27c

binder_new_node+0x50/0x700

binder_transaction+0x35ac/0x6f74

binder_thread_write+0xfb8/0x42a0

binder_ioctl+0x18f0/0x25ac

__arm64_sys_ioctl+0x124/0x190

Freed by task 637:

kfree+0xf0/0x330

binder_thread_read+0x1e88/0x3a68

binder_ioctl+0x16d8/0x25ac

__arm64_sys_ioctl+0x124/0x190

==================================================================

Fix the race by taking a temporary reference on the node before

releasing the proc->inner lock. This ensures the node remains alive

while in use.