binder: avoid race conditions when enqueuing txn

Currently, the transaction complete work item is queued
after the transaction. This means that it is possible
for the transaction to be handled and a reply to be
enqueued in the current thread before the transaction
complete is enqueued, which violates the protocol
with userspace who may not expect the transaction
complete. Fixed by always enqueing the transaction
complete first.

Also, once the transaction is enqueued, it is unsafe
to access since it might be freed. Currently,
t->flags is accessed to determine whether a sync
wake is needed. Changed to access tr->flags
instead.

Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index f17d1dfa5b027f3792e32aa233532bb6de544541..71faf548482d3ff6f7e457d1ccc453ddc9f91ffd 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1799,6 +1799,9 @@ static void binder_transaction(struct binder_proc *proc,
                        goto err_bad_object_type;
                }
        }
+       tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
+       list_add_tail(&tcomplete->entry, &thread->todo);
+
        if (reply) {
                BUG_ON(t->buffer->async_transaction != 0);
                binder_pop_transaction(target_thread, in_reply_to);
@@ -1818,10 +1821,8 @@ static void binder_transaction(struct binder_proc *proc,
        }
        t->work.type = BINDER_WORK_TRANSACTION;
        list_add_tail(&t->work.entry, target_list);
-       tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
-       list_add_tail(&tcomplete->entry, &thread->todo);
        if (target_wait) {
-               if (reply || !(t->flags & TF_ONE_WAY))
+               if (reply || !(tr->flags & TF_ONE_WAY))
                        wake_up_interruptible_sync(target_wait);
                else
                        wake_up_interruptible(target_wait);