linux-kernel - Re: [PATCH] binder: fix memory corruption in binder

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Date:   Mon, 11 Sep 2017 08:40:10 -0700
From:   Todd Kjos <tkjos@...gle.com>
To:     Amit Pundir <amit.pundir@...aro.org>
Cc:     Todd Kjos <tkjos@...roid.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Martijn Coenen <maco@...gle.com>,
        Xu Yiping <xuyiping@...ilicon.com>, gengyanping@...ilicon.com,
        shiwanglai@...ilicon.com, John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH] binder: fix memory corruption in binder_transaction binder

(resend in plain-text mode -- sorry about that)

Amit,

Are you sure this patch is the culprit? That is pretty surprising
since this change can only be hit in a uncommon case (the target node
is valid when we start creating the transaction, but dead when we
check right before sending it) so it is unlikely to be hit during a
normal boot. It also fixes a corruption -- so if you were actually
hitting the case, it would likely have caused issues before and not
now. Take a look at it and see if you think it is really possible.

I just booted hikey to Android with this patch 10 times in a row with
no issues (used hikey-linaro 4.9 kernel which has this patch).

-Todd

> On Mon, Sep 11, 2017 at 5:18 AM, Amit Pundir <amit.pundir@...aro.org> wrote:
>>
>> On 5 September 2017 at 22:51, Todd Kjos <tkjos@...roid.com> wrote:
>> > From: Xu YiPing <xuyiping@...ilicon.com>
>> >
>> > commit 7a4408c6bd3e ("binder: make sure accesses to proc/thread are
>> > safe") made a change to enqueue tcomplete to thread->todo before
>> > enqueuing the transaction. However, in err_dead_proc_or_thread case,
>> > the tcomplete is directly freed, without dequeued. It may cause the
>> > thread->todo list to be corrupted.
>> >
>> > So, dequeue it before freeing.
>>
>> I see Android boot loops with this patch on hikey tracking
>> linux/master branch. 1st boot is fine but hikey runs into an
>> unexpected short boot loops on 2nd and successive boots.
>>
>> It takes about 3-4 iterations to finally come to sane state and boot
>> to UI. I don't see this behaviour if I revert this patch.
>>
>> Regards,
>> Amit Pundir
>>
>> >
>> > Signed-off-by: Xu YiPing <xuyiping@...ilicon.com>
>> > Signed-off-by: Todd Kjos <tkjos@...gle.com>
>> > ---
>> >  drivers/android/binder.c | 1 +
>> >  1 file changed, 1 insertion(+)
>> >
>> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
>> > index d055b3f2a207..96cc28afa383 100644
>> > --- a/drivers/android/binder.c
>> > +++ b/drivers/android/binder.c
>> > @@ -3083,6 +3083,7 @@ static void binder_transaction(struct binder_proc
>> > *proc,
>> >  err_dead_proc_or_thread:
>> >         return_error = BR_DEAD_REPLY;
>> >         return_error_line = __LINE__;
>> > +       binder_dequeue_work(proc, tcomplete);
>> >  err_translate_failed:
>> >  err_bad_object_type:
>> >  err_bad_offset:
>> > --
>> > 2.14.1.581.gf28d330327-goog
>> >
>
>