Re: [RFC] android/hal-audio: Fix wrong memory access

[Andrei Emeltchenko <andrei.emeltchenko.news@gmail.com>]

On Mon, May 26, 2014 at 02:59:31PM +0200, Andrzej Kaczmarek wrote:
> Hi Marcel,
> 
> On 26 May 2014 14:48, Marcel Holtmann <marcel@holtmann.org> wrote:
> > Hi Andrzej,
> >
> >>>> downmix_buf is allocated to have buffer size FIXED_BUFFER_SIZE / 2, when
> >>>> we access it as (int16_t *) we shall device index by 2.
> >>>> ---
> >>>> android/hal-audio.c | 2 +-
> >>>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/android/hal-audio.c b/android/hal-audio.c
> >>>> index 7305bb6..96fa5c3 100644
> >>>> --- a/android/hal-audio.c
> >>>> +++ b/android/hal-audio.c
> >>>> @@ -984,7 +984,7 @@ static void downmix_to_mono(struct a2dp_stream_out *out, const uint8_t *buffer,
> >>>>      int16_t *output = (void *) out->downmix_buf;
> >>>>      size_t i;
> >>>>
> >>>> -     for (i = 0; i < bytes / 2; i++) {
> >>>> +     for (i = 0; i < bytes / (2 * sizeof(int16_t)); i++) {
> >>>>              int16_t l = le16_to_cpu(get_unaligned(&input[i * 2]));
> >>>>              int16_t r = le16_to_cpu(get_unaligned(&input[i * 2 + 1]));
> >>>
> >>> I wonder actually what this get_unaligned is doing here? You cast the const void into const int16_t buffer. Is this really needed? Where is our input and output buffer coming from? Aren’t these aligned anyway? Meaning aren’t they allocated?
> >>
> >> We have this buffer from AudioFlinger so we don't actually know
> >> alignment or if this is pointer to beginning of some internal buffer
> >> (it's most probably both, but I don't think we should assume this).
> >
> > and audio system that does not give you a guarantee here on the alignment is utterly screwed up. Seriously, that is just bad for performance. Especially bad on ARM CPUs, so I doubt that they have not thought about this.
> 
> This is only to be on safe side and in terms of performance it does
> not really matter here since this code won't probably be used at all -

It was definitely not used. It crashes. I have modified code for SCO where
downmix was used.

Best regards 
Andrei Emeltchenko