rust_binder: clear freeze listener on node removal

Generally userspace is supposed to explicitly clear freeze listeners
before they drop the refcount on the node ref to zero, but there's
nothing forcing that. Currently, in this scenario the freeze listener
remains in the freeze_listeners rbtree and in the remote node's freeze
listener list, even though the ref for which the listener is registered
is gone. This could potentially lead to a memory leak due to a refcount
cycle. Thus, remove the freeze listener in this scenario.

Cc: stable <stable@kernel.org>
Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver")
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260703-remove-freeze-on-remove-node-v3-1-6e0c4547af46@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder/freeze.rs b/drivers/android/binder/freeze.rs
index 53b60035639aa9e41c2c6a450953df949a3ce354..f4df14568b25243f4479b719a535bce7dcbaaa2b 100644 (file)
--- a/drivers/android/binder/freeze.rs
+++ b/drivers/android/binder/freeze.rs
@@ -154,10 +154,17 @@ impl DeliverToRead for FreezeMessage {
 }
 
 impl FreezeListener {
-    pub(crate) fn on_process_exit(&self, proc: &Arc<Process>) {
+    /// Called when this freeze listener is cleared abnormally.
+    ///
+    /// This occurs either because the process exited or because the process dropped its last
+    /// refcount on the node ref without explicitly removing the freeze listener first.
+    ///
+    /// The returned `KVVec` is just a value that should be dropped outside of the lock.
+    pub(crate) fn on_process_cleanup(&self, proc: &Process) -> KVVec<Arc<Process>> {
         if !self.is_clearing {
-            self.node.remove_freeze_listener(proc);
+            return self.node.remove_freeze_listener(proc);
         }
+        KVVec::new()
     }
 }
 

diff --git a/drivers/android/binder/node.rs b/drivers/android/binder/node.rs
index 69f757ff7461e0fb6b2b36b5ade1deb53c0c9339..c10148e9069f3ba8ef53c5540dd811ee668a6805 100644 (file)
--- a/drivers/android/binder/node.rs
+++ b/drivers/android/binder/node.rs
@@ -682,12 +682,13 @@ impl Node {
         }
     }
 
-    pub(crate) fn remove_freeze_listener(&self, p: &Arc<Process>) {
-        let _unused_capacity;
+    pub(crate) fn remove_freeze_listener(&self, p: &Process) -> KVVec<Arc<Process>> {
         let mut guard = self.owner.inner.lock();
         let inner = self.inner.access_mut(&mut guard);
         let len = inner.freeze_list.len();
-        inner.freeze_list.retain(|proc| !Arc::ptr_eq(proc, p));
+        inner
+            .freeze_list
+            .retain(|proc| !core::ptr::eq::<Process>(&**proc, p));
         if len == inner.freeze_list.len() {
             pr_warn!(
                 "Could not remove freeze listener for {}\n",
@@ -695,8 +696,9 @@ impl Node {
             );
         }
         if inner.freeze_list.is_empty() {
-            _unused_capacity = mem::take(&mut inner.freeze_list);
+            return mem::take(&mut inner.freeze_list);
         }
+        KVVec::new()
     }
 
     pub(crate) fn freeze_list<'a>(&'a self, guard: &'a ProcessInner) -> &'a [Arc<Process>] {

diff --git a/drivers/android/binder/process.rs b/drivers/android/binder/process.rs
index ca664fda8e8107d009cb0285831dbf326dd54eec..cdd1a9079726673190a53e005f4cb1d391133ca3 100644 (file)
--- a/drivers/android/binder/process.rs
+++ b/drivers/android/binder/process.rs
@@ -946,6 +946,8 @@ impl Process {
 
         // To preserve original binder behaviour, we only fail requests where the manager tries to
         // increment references on itself.
+        let _to_free_freeze_listener;
+        let _to_free_freeze_listener_cleanup;
         let mut refs = self.node_refs.lock();
         if let Some(info) = refs.by_handle.get_mut(&handle) {
             if info.node_ref().update(inc, strong) {
@@ -961,6 +963,14 @@ impl Process {
                 unsafe { info.node_ref2().node.remove_node_info(info) };
 
                 let id = info.node_ref().node.global_id();
+
+                if let Some(freeze) = *info.freeze() {
+                    if let Some(fl) = refs.freeze_listeners.remove(&freeze) {
+                        _to_free_freeze_listener_cleanup = fl.on_process_cleanup(&self);
+                        _to_free_freeze_listener = fl;
+                    }
+                }
+
                 refs.by_handle.remove(&handle);
                 refs.by_node.remove(&id);
                 refs.handle_is_present.release_id(handle as usize);
@@ -1384,7 +1394,7 @@ impl Process {
         // Clean up freeze listeners.
         let freeze_listeners = take(&mut self.node_refs.lock().freeze_listeners);
         for listener in freeze_listeners.values() {
-            listener.on_process_exit(&self);
+            listener.on_process_cleanup(&self);
         }
         drop(freeze_listeners);