binder: prevent transactions to context manager from its own process.

commit 49ed9694 upstream.

Currently, a transaction to context manager from its own process
is prevented by checking if its binder_proc struct is the same as
that of the sender. However, this would not catch cases where the
process opens the binder device again and uses the new fd to send
a transaction to the context manager.

Reported-by:  <syzbot+8b3c354d33c4ac78bfad@syzkaller.appspotmail.com>
Signed-off-by: Hridya Valsaraju <hridya@google.com>
Acked-by: Todd Kjos <tkjos@google.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20190715191804.112933-1-hridya@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>