ANDROID: binder: remove waitqueue when thread exits.

commit f5cb779ba16334b45ba8946d6bfa6d9834d1527f upstream.

binder_poll() passes the thread->wait waitqueue that
can be slept on for work. When a thread that uses
epoll explicitly exits using BINDER_THREAD_EXIT,
the waitqueue is freed, but it is never removed
from the corresponding epoll data structure. When
the process subsequently exits, the epoll cleanup
code tries to access the waitlist, which results in
a use-after-free.

Prevent this by using POLLFREE when the thread exits.

Signed-off-by: Martijn Coenen <maco@android.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: stable <stable@vger.kernel.org> # 4.14
[backport BINDER_LOOPER_STATE_POLL logic as well]
Signed-off-by: Mattias Nissler <mnissler@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 01eb2a2a3746b5eaff953d9f86c574ff7992ba1a..5c13a6eb4fea358b85c8d70e5789aa5d4c13b4ec 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -334,7 +334,8 @@ enum {
        BINDER_LOOPER_STATE_EXITED      = 0x04,
        BINDER_LOOPER_STATE_INVALID     = 0x08,
        BINDER_LOOPER_STATE_WAITING     = 0x10,
-       BINDER_LOOPER_STATE_NEED_RETURN = 0x20
+       BINDER_LOOPER_STATE_NEED_RETURN = 0x20,
+       BINDER_LOOPER_STATE_POLL        = 0x40,
 };
 
 struct binder_thread {
@@ -2610,6 +2611,18 @@ static int binder_free_thread(struct binder_proc *proc,
                } else
                        BUG();
        }
+
+       /*
+        * If this thread used poll, make sure we remove the waitqueue
+        * from any epoll data structures holding it with POLLFREE.
+        * waitqueue_active() is safe to use here because we're holding
+        * the global lock.
+        */
+       if ((thread->looper & BINDER_LOOPER_STATE_POLL) &&
+           waitqueue_active(&thread->wait)) {
+               wake_up_poll(&thread->wait, POLLHUP | POLLFREE);
+       }
+
        if (send_reply)
                binder_send_failed_reply(send_reply, BR_DEAD_REPLY);
        binder_release_work(&thread->todo);
@@ -2633,6 +2646,8 @@ static unsigned int binder_poll(struct file *filp,
                return POLLERR;
        }
 
+       thread->looper |= BINDER_LOOPER_STATE_POLL;
+
        wait_for_proc_work = thread->transaction_stack == NULL &&
                list_empty(&thread->todo) && thread->return_error == BR_OK;