linux-kernel - Re: [PATCH] android: binder: check result of binder_get_thread() in binder

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Date:   Mon, 8 May 2017 13:46:42 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Martijn Coenen <maco@...gle.com>,
        Douglas Anderson <dianders@...omium.org>,
        devel@...verdev.osuosl.org, lkml <linux-kernel@...r.kernel.org>,
        Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH] android: binder: check result of binder_get_thread() in binder_poll()

On Mon, May 8, 2017 at 1:43 PM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> If binder_get_thread() fails to give us a thread data, we should avoid
> dereferencing a NULL pointer and return POLLERR instead.
>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

Pulling Todd Kjos in on this too.
-john

> ---
>  drivers/android/binder.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index aae4d8d4be36..66ed714fedd5 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -3103,18 +3103,22 @@ static unsigned int binder_poll(struct file *filp,
>                                 struct poll_table_struct *wait)
>  {
>         struct binder_proc *proc = filp->private_data;
> -       struct binder_thread *thread = NULL;
> +       struct binder_thread *thread;
>         int wait_for_proc_work;
>
>         binder_lock(__func__);
>
>         thread = binder_get_thread(proc);
> -
> -       wait_for_proc_work = thread->transaction_stack == NULL &&
> -               list_empty(&thread->todo) && thread->return_error == BR_OK;
> +       if (thread)
> +               wait_for_proc_work = thread->transaction_stack == NULL &&
> +                                    list_empty(&thread->todo) &&
> +                                    thread->return_error == BR_OK;
>
>         binder_unlock(__func__);
>
> +       if (!thread)
> +               return POLLERR;
> +
>         if (wait_for_proc_work) {
>                 if (binder_has_proc_work(proc, thread))
>                         return POLLIN;
> --
> 2.13.0.rc1.294.g07d810a77f-goog
>
>
> --
> Dmitry