binder: BINDER_FREEZE ioctl

Frozen tasks can't process binder transactions, so a way is required to
inform transmitting ends of communication failures due to the frozen
state of their receiving counterparts. Additionally, races are possible
between transitions to frozen state and binder transactions enqueued to
a specific process.

Implement BINDER_FREEZE ioctl for user space to inform the binder driver
about the intention to freeze or unfreeze a process. When the ioctl is
called, block the caller until any pending binder transactions toward
the target process are flushed. Return an error to transactions to
processes marked as frozen.

Co-developed-by: Todd Kjos <tkjos@google.com>
Acked-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Marco Ballesio <balejs@google.com>
Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Li Li <dualli@google.com>
Link: https://lore.kernel.org/r/20210316011630.1121213-2-dualli@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binder.c

@@ -1506,6 +1506,12 @@ static void binder_free_transaction(struct binder_transaction *t)
 
 	if (target_proc) {
 		binder_inner_proc_lock(target_proc);
+		target_proc->outstanding_txns--;
+		if (target_proc->outstanding_txns < 0)
+			pr_warn("%s: Unexpected outstanding_txns %d\n",
+				__func__, target_proc->outstanding_txns);
+		if (!target_proc->outstanding_txns && target_proc->is_frozen)
+			wake_up_interruptible_all(&target_proc->freeze_wait);
 		if (t->buffer)
 			t->buffer->transaction = NULL;
 		binder_inner_proc_unlock(target_proc);
@@ -2331,10 +2337,11 @@ static int binder_fixup_parent(struct binder_transaction *t,
  * If the @thread parameter is not NULL, the transaction is always queued
  * to the waitlist of that specific thread.
  *
- * Return:	true if the transactions was successfully queued
- *		false if the target process or thread is dead
+ * Return:	0 if the transaction was successfully queued
+ *		BR_DEAD_REPLY if the target process or thread is dead
+ *		BR_FROZEN_REPLY if the target process or thread is frozen
  */
-static bool binder_proc_transaction(struct binder_transaction *t,
+static int binder_proc_transaction(struct binder_transaction *t,
 				    struct binder_proc *proc,
 				    struct binder_thread *thread)
 {
@@ -2354,10 +2361,11 @@ static bool binder_proc_transaction(struct binder_transaction *t,
 
 	binder_inner_proc_lock(proc);
 
-	if (proc->is_dead || (thread && thread->is_dead)) {
+	if ((proc->is_frozen && !oneway) || proc->is_dead ||
+			(thread && thread->is_dead)) {
 		binder_inner_proc_unlock(proc);
 		binder_node_unlock(node);
-		return false;
+		return proc->is_frozen ? BR_FROZEN_REPLY : BR_DEAD_REPLY;
 	}
 
 	if (!thread && !pending_async)
@@ -2373,10 +2381,11 @@ static bool binder_proc_transaction(struct binder_transaction *t,
 	if (!pending_async)
 		binder_wakeup_thread_ilocked(proc, thread, !oneway /* sync */);
 
+	proc->outstanding_txns++;
 	binder_inner_proc_unlock(proc);
 	binder_node_unlock(node);
 
-	return true;
+	return 0;
 }
 
 /**
@@ -3013,13 +3022,16 @@ static void binder_transaction(struct binder_proc *proc,
 	if (reply) {
 		binder_enqueue_thread_work(thread, tcomplete);
 		binder_inner_proc_lock(target_proc);
-		if (target_thread->is_dead) {
+		if (target_thread->is_dead || target_proc->is_frozen) {
+			return_error = target_thread->is_dead ?
+				BR_DEAD_REPLY : BR_FROZEN_REPLY;
 			binder_inner_proc_unlock(target_proc);
 			goto err_dead_proc_or_thread;
 		}
 		BUG_ON(t->buffer->async_transaction != 0);
 		binder_pop_transaction_ilocked(target_thread, in_reply_to);
 		binder_enqueue_thread_work_ilocked(target_thread, &t->work);
+		target_proc->outstanding_txns++;
 		binder_inner_proc_unlock(target_proc);
 		wake_up_interruptible_sync(&target_thread->wait);
 		binder_free_transaction(in_reply_to);
@@ -3038,7 +3050,9 @@ static void binder_transaction(struct binder_proc *proc,
 		t->from_parent = thread->transaction_stack;
 		thread->transaction_stack = t;
 		binder_inner_proc_unlock(proc);
-		if (!binder_proc_transaction(t, target_proc, target_thread)) {
+		return_error = binder_proc_transaction(t,
+				target_proc, target_thread);
+		if (return_error) {
 			binder_inner_proc_lock(proc);
 			binder_pop_transaction_ilocked(thread, t);
 			binder_inner_proc_unlock(proc);
@@ -3048,7 +3062,8 @@ static void binder_transaction(struct binder_proc *proc,
 		BUG_ON(target_node == NULL);
 		BUG_ON(t->buffer->async_transaction != 1);
 		binder_enqueue_thread_work(thread, tcomplete);
-		if (!binder_proc_transaction(t, target_proc, NULL))
+		return_error = binder_proc_transaction(t, target_proc, NULL);
+		if (return_error)
 			goto err_dead_proc_or_thread;
 	}
 	if (target_thread)
@@ -3065,7 +3080,6 @@ static void binder_transaction(struct binder_proc *proc,
 	return;
 
 err_dead_proc_or_thread:
-	return_error = BR_DEAD_REPLY;
 	return_error_line = __LINE__;
 	binder_dequeue_work(proc, tcomplete);
 err_translate_failed:
@@ -4298,6 +4312,9 @@ static void binder_free_proc(struct binder_proc *proc)
 
 	BUG_ON(!list_empty(&proc->todo));
 	BUG_ON(!list_empty(&proc->delivered_death));
+	if (proc->outstanding_txns)
+		pr_warn("%s: Unexpected outstanding_txns %d\n",
+			__func__, proc->outstanding_txns);
 	device = container_of(proc->context, struct binder_device, context);
 	if (refcount_dec_and_test(&device->ref)) {
 		kfree(proc->context->name);
@@ -4359,6 +4376,7 @@ static int binder_thread_release(struct binder_proc *proc,
 			     (t->to_thread == thread) ? "in" : "out");
 
 		if (t->to_thread == thread) {
+			thread->proc->outstanding_txns--;
 			t->to_proc = NULL;
 			t->to_thread = NULL;
 			if (t->buffer) {
@@ -4609,6 +4627,45 @@ static int binder_ioctl_get_node_debug_info(struct binder_proc *proc,
 	return 0;
 }
 
+static int binder_ioctl_freeze(struct binder_freeze_info *info,
+			       struct binder_proc *target_proc)
+{
+	int ret = 0;
+
+	if (!info->enable) {
+		binder_inner_proc_lock(target_proc);
+		target_proc->is_frozen = false;
+		binder_inner_proc_unlock(target_proc);
+		return 0;
+	}
+
+	/*
+	 * Freezing the target. Prevent new transactions by
+	 * setting frozen state. If timeout specified, wait
+	 * for transactions to drain.
+	 */
+	binder_inner_proc_lock(target_proc);
+	target_proc->is_frozen = true;
+	binder_inner_proc_unlock(target_proc);
+
+	if (info->timeout_ms > 0)
+		ret = wait_event_interruptible_timeout(
+			target_proc->freeze_wait,
+			(!target_proc->outstanding_txns),
+			msecs_to_jiffies(info->timeout_ms));
+
+	if (!ret && target_proc->outstanding_txns)
+		ret = -EAGAIN;
+
+	if (ret < 0) {
+		binder_inner_proc_lock(target_proc);
+		target_proc->is_frozen = false;
+		binder_inner_proc_unlock(target_proc);
+	}
+
+	return ret;
+}
+
 static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	int ret;
@@ -4727,6 +4784,66 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		}
 		break;
 	}
+	case BINDER_FREEZE: {
+		struct binder_freeze_info info;
+		struct binder_proc **target_procs = NULL, *target_proc;
+		int target_procs_count = 0, i = 0;
+
+		ret = 0;
+
+		if (copy_from_user(&info, ubuf, sizeof(info))) {
+			ret = -EFAULT;
+			goto err;
+		}
+
+		mutex_lock(&binder_procs_lock);
+		hlist_for_each_entry(target_proc, &binder_procs, proc_node) {
+			if (target_proc->pid == info.pid)
+				target_procs_count++;
+		}
+
+		if (target_procs_count == 0) {
+			mutex_unlock(&binder_procs_lock);
+			ret = -EINVAL;
+			goto err;
+		}
+
+		target_procs = kcalloc(target_procs_count,
+				       sizeof(struct binder_proc *),
+				       GFP_KERNEL);
+
+		if (!target_procs) {
+			mutex_unlock(&binder_procs_lock);
+			ret = -ENOMEM;
+			goto err;
+		}
+
+		hlist_for_each_entry(target_proc, &binder_procs, proc_node) {
+			if (target_proc->pid != info.pid)
+				continue;
+
+			binder_inner_proc_lock(target_proc);
+			target_proc->tmp_ref++;
+			binder_inner_proc_unlock(target_proc);
+
+			target_procs[i++] = target_proc;
+		}
+		mutex_unlock(&binder_procs_lock);
+
+		for (i = 0; i < target_procs_count; i++) {
+			if (ret >= 0)
+				ret = binder_ioctl_freeze(&info,
+							  target_procs[i]);
+
+			binder_proc_dec_tmpref(target_procs[i]);
+		}
+
+		kfree(target_procs);
+
+		if (ret < 0)
+			goto err;
+		break;
+	}
 	default:
 		ret = -EINVAL;
 		goto err;
@@ -4823,6 +4940,7 @@ static int binder_open(struct inode *nodp, struct file *filp)
 	get_task_struct(current->group_leader);
 	proc->tsk = current->group_leader;
 	INIT_LIST_HEAD(&proc->todo);
+	init_waitqueue_head(&proc->freeze_wait);
 	proc->default_priority = task_nice(current);
 	/* binderfs stashes devices in i_private */
 	if (is_binderfs_device(nodp)) {
@@ -5035,6 +5153,7 @@ static void binder_deferred_release(struct binder_proc *proc)
 	proc->tmp_ref++;
 
 	proc->is_dead = true;
+	proc->is_frozen = false;
 	threads = 0;
 	active_transactions = 0;
 	while ((n = rb_first(&proc->threads))) {

drivers/android/binder_internal.h

@@ -367,9 +367,18 @@ struct binder_ref {
  *                        (protected by binder_deferred_lock)
  * @deferred_work:        bitmap of deferred work to perform
  *                        (protected by binder_deferred_lock)
+ * @outstanding_txns:     number of transactions to be transmitted before
+ *                        processes in freeze_wait are woken up
+ *                        (protected by @inner_lock)
  * @is_dead:              process is dead and awaiting free
  *                        when outstanding transactions are cleaned up
  *                        (protected by @inner_lock)
+ * @is_frozen:            process is frozen and unable to service
+ *                        binder transactions
+ *                        (protected by @inner_lock)
+ * @freeze_wait:          waitqueue of processes waiting for all outstanding
+ *                        transactions to be processed
+ *                        (protected by @inner_lock)
  * @todo:                 list of work for this process
  *                        (protected by @inner_lock)
  * @stats:                per-process binder statistics
@@ -410,7 +419,10 @@ struct binder_proc {
 	struct task_struct *tsk;
 	struct hlist_node deferred_work_node;
 	int deferred_work;
+	int outstanding_txns;
 	bool is_dead;
+	bool is_frozen;
+	wait_queue_head_t freeze_wait;
 
 	struct list_head todo;
 	struct binder_stats stats;

include/uapi/linux/android/binder.h

@@ -217,6 +217,12 @@ struct binder_node_info_for_ref {
 	__u32            reserved3;
 };
 
+struct binder_freeze_info {
+	__u32            pid;
+	__u32            enable;
+	__u32            timeout_ms;
+};
+
 #define BINDER_WRITE_READ		_IOWR('b', 1, struct binder_write_read)
 #define BINDER_SET_IDLE_TIMEOUT		_IOW('b', 3, __s64)
 #define BINDER_SET_MAX_THREADS		_IOW('b', 5, __u32)
@@ -227,6 +233,7 @@ struct binder_node_info_for_ref {
 #define BINDER_GET_NODE_DEBUG_INFO	_IOWR('b', 11, struct binder_node_debug_info)
 #define BINDER_GET_NODE_INFO_FOR_REF	_IOWR('b', 12, struct binder_node_info_for_ref)
 #define BINDER_SET_CONTEXT_MGR_EXT	_IOW('b', 13, struct flat_binder_object)
+#define BINDER_FREEZE			_IOW('b', 14, struct binder_freeze_info)
 
 /*
  * NOTE: Two special error codes you should check for when calling
@@ -408,6 +415,12 @@ enum binder_driver_return_protocol {
 	 * The last transaction (either a bcTRANSACTION or
 	 * a bcATTEMPT_ACQUIRE) failed (e.g. out of memory).  No parameters.
 	 */
+
+	BR_FROZEN_REPLY = _IO('r', 18),
+	/*
+	 * The target of the last transaction (either a bcTRANSACTION or
+	 * a bcATTEMPT_ACQUIRE) is frozen.  No parameters.
+	 */
 };
 
 enum binder_driver_command_protocol {