linux-kernel - Re: [PATCH v2] dma-buf: dma-heap: Add a size check for allocation

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Date:   Mon, 3 Jan 2022 10:57:30 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     guangming.cao@...iatek.com
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        Christian König <christian.koenig@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:DMA-BUF HEAPS FRAMEWORK" <linux-media@...r.kernel.org>,
        "open list:DMA-BUF HEAPS FRAMEWORK" <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA-BUF HEAPS FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Bo Song <bo.song@...iatek.com>,
        Libo Kang <libo.kang@...iatek.com>,
        jianjiao zeng <jianjiao.zeng@...iatek.com>,
        mingyuan ma <mingyuan.ma@...iatek.com>,
        Yunfei Wang <yf.wang@...iatek.com>, wsd_upstream@...iatek.com
Subject: Re: [PATCH v2] dma-buf: dma-heap: Add a size check for allocation

On Mon, Dec 27, 2021 at 1:52 AM <guangming.cao@...iatek.com> wrote:
>
> From: Guangming <Guangming.Cao@...iatek.com>
>

Thanks for submitting this!

> Add a size check for allcation since the allocation size is

nit: "allocation" above.

> always less than the total DRAM size.

In general, it might be good to add more context to the commit message
to better answer *why* this change is needed rather than what the
change is doing.  ie: What negative thing happens without this change?
And so how does this change avoid or improve things?


> Signed-off-by: Guangming <Guangming.Cao@...iatek.com>
> Signed-off-by: jianjiao zeng <jianjiao.zeng@...iatek.com>
> ---
> v2: 1. update size limitation as total_dram page size.
>     2. update commit message
> ---
>  drivers/dma-buf/dma-heap.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index 56bf5ad01ad5..e39d2be98d69 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -55,6 +55,8 @@ static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
>         struct dma_buf *dmabuf;
>         int fd;
>
> +       if (len / PAGE_SIZE > totalram_pages())
> +               return -EINVAL;

This seems sane. I know ION used to have some 1/2 of memory cap to
avoid unnecessary memory pressure on crazy allocations.

Could you send again with an improved commit message?

thanks
-john