[PATCH v2 1/8] binder: fix node UAF in binder_add_freeze_work()

[Carlos Llamas <cmllamas@google.com>]

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>
---
 drivers/android/binder.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 978740537a1a..4d90203ea048 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -5552,6 +5552,7 @@ static bool binder_txns_pending_ilocked(struct binder_proc *proc)
 
 static void binder_add_freeze_work(struct binder_proc *proc, bool is_frozen)
 {
+	struct binder_node *prev = NULL;
 	struct rb_node *n;
 	struct binder_ref *ref;
 
@@ -5560,7 +5561,10 @@ static void binder_add_freeze_work(struct binder_proc *proc, bool is_frozen)
 		struct binder_node *node;
 
 		node = rb_entry(n, struct binder_node, rb_node);
+		binder_inc_node_tmpref_ilocked(node);
 		binder_inner_proc_unlock(proc);
+		if (prev)
+			binder_put_node(prev);
 		binder_node_lock(node);
 		hlist_for_each_entry(ref, &node->refs, node_entry) {
 			/*
@@ -5586,10 +5590,13 @@ static void binder_add_freeze_work(struct binder_proc *proc, bool is_frozen)
 			}
 			binder_inner_proc_unlock(ref->proc);
 		}
+		prev = node;
 		binder_node_unlock(node);
 		binder_inner_proc_lock(proc);
 	}
 	binder_inner_proc_unlock(proc);
+	if (prev)
+		binder_put_node(prev);
 }
 
 static int binder_ioctl_freeze(struct binder_freeze_info *info,
-- 
2.46.1.824.gd892dcdcdd-goog