On Sun, Oct 6, 2019 at 7:23 PM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Martijn Coenen <maco@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
> Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
> Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.14
> [backport BINDER_LOOPER_STATE_POLL logic as well]
> Signed-off-by: Mattias Nissler <mnissler@xxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> 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.
This should be "global lock" in 4.9 and 4.4 :)
Otherwise LGTM, thanks!
Martijn
> + */
> + 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;
>
>
>
