On Sun, Oct 06, 2019 at 10:32:02AM -0700, Eric Biggers wrote:
> On Sun, Oct 06, 2019 at 07:21:17PM +0200, Greg Kroah-Hartman wrote:
> > From: Martijn Coenen <m...@android.com>
> >
> > 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 <m...@android.com>
> > Reported-by: syzbot <syzkal...@googlegroups.com>
> > Cc: stable <sta...@vger.kernel.org> # 4.14
> > [backport BINDER_LOOPER_STATE_POLL logic as well]
> > Signed-off-by: Mattias Nissler <mniss...@chromium.org>
> > Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> > ---
> > drivers/android/binder.c | 17 ++++++++++++++++-
> > 1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > --- 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 {
> > @@ -2628,6 +2629,18 @@ static int binder_free_thread(struct bin
> > } 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 inner 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);
> > @@ -2651,6 +2664,8 @@ static unsigned int binder_poll(struct f
> > 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;
> >
>
> Are you sure this backport is correct, given that in 4.9, binder_poll()
> sometimes uses proc->wait instead of thread->wait?:
>
> wait_for_proc_work = thread->transaction_stack == NULL &&
> list_empty(&thread->todo) && thread->return_error == BR_OK;
>
> binder_unlock(__func__);
>
> if (wait_for_proc_work) {
> if (binder_has_proc_work(proc, thread))
> return POLLIN;
> poll_wait(filp, &proc->wait, wait);
> if (binder_has_proc_work(proc, thread))
> return POLLIN;
> } else {
> if (binder_has_thread_work(thread))
> return POLLIN;
> poll_wait(filp, &thread->wait, wait);
> if (binder_has_thread_work(thread))
> return POLLIN;
> }
> return 0;
I _think_ the backport is correct, and I know someone has verified that
the 4.4.y backport works properly and I don't see much difference here
from that version.
But I will defer to Todd and Martijn here, as they know this code _WAY_
better than I do. The codebase has changed a lot from 4.9.y to 4.14.y
so it makes it hard to do equal comparisons simply.
Todd and Martijn, thoughts?
thanks,
greg k-h
