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.

Fixes: d579b04a52a1 ("binder: frozen notification")
Cc: stable@vger.kernel.org
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20240926233632.821189-2-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>