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

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Date:   Mon, 8 May 2017 13:56:06 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Martijn Coenen <maco@...gle.com>, 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()

Dmitry,

On Mon, May 8, 2017 at 1:46 PM, John Stultz <john.stultz@...aro.org> wrote:
> 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;
>> --

I'm no expert on the poll function, but I agree that it's wise to
check the result of binder_get_thread() since it can return NULL.
FWIW:

Reviewed-by: Douglas Anderson <dianders@...omium.org>