[PATCH 1/2] ALSA: memalloc: Align buffer allocations in page size

[Lars-Peter Clausen]

On 12/18/20 3:56 PM, Takashi Iwai wrote:
> Currently the standard memory allocator (snd_dma_malloc_pages*())
> passes the byte size to allocate as is.  Most of the backends
> allocates real pages, hence the actual allocations are aligned in page
> size.  However, the genalloc doesn't seem assuring the size alignment,
> hence it may result in the access outside the buffer when the whole
> memory pages are exposed via mmap.
>
> For avoiding such inconsistencies, this patch makes the allocation
> size always to be aligned in page size.
>
> Note that, after this change, snd_dma_buffer.bytes field contains the
> aligned size, not the originally requested size.  This value is also
> used for releasing the pages in return.
>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>

FWIW

Reviewed-by: Lars-Peter Clausen <lars at metafoo.de>

> ---
>   sound/core/memalloc.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c
> index 0f335162f87c..966bef5acc75 100644
> --- a/sound/core/memalloc.c
> +++ b/sound/core/memalloc.c
> @@ -133,6 +133,7 @@ int snd_dma_alloc_pages(int type, struct device *device, size_t size,
>   	if (WARN_ON(!dmab))
>   		return -ENXIO;
>   
> +	size = PAGE_ALIGN(size);
>   	dmab->dev.type = type;
>   	dmab->dev.dev = device;
>   	dmab->bytes = 0;