Re: [PATCH 10/13] media: imx7-media-csi: Don't use GFP_DMA when calling dma_alloc_coherent()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [Critical] Integer overflow in `sizeimage` calculation and signedness truncation in `imx7_csi_alloc_dma_buf()` allow userspace to trigger a massive out-of-bounds DMA write, corrupting kernel memory.
--

commit 007baffc77bd7059db343099782a06610465cf12
Author: Baoquan He <hebaoquan@kylinos.cn>
Subject: media: imx7-media-csi: Don't use GFP_DMA when calling dma_alloc_coherent()

This commit removes the redundant GFP_DMA flag from the dma_alloc_coherent()
call in imx7_csi_alloc_dma_buf(). The DMA core already handles device
addressing limitations and ignores GFP_DMA.

> diff --git a/drivers/media/platform/nxp/imx7-media-csi.c b/drivers/media/platform/nxp/imx7-media-csi.c
> index 7ddc7ba06e3d4..22c0cbdc92bfb 100644
> --- a/drivers/media/platform/nxp/imx7-media-csi.c
> +++ b/drivers/media/platform/nxp/imx7-media-csi.c
> @@ -466,7 +466,7 @@ static int imx7_csi_alloc_dma_buf(struct imx7_csi *csi,
>  
>  	buf->len = PAGE_ALIGN(size);
>  	buf->virt = dma_alloc_coherent(csi->dev, buf->len, &buf->dma_addr,
> -				       GFP_DMA | GFP_KERNEL);
> +				       GFP_KERNEL);
[Severity: Critical]
This isn't a bug introduced by this patch, but could this allocation lead to
arbitrary kernel memory corruption?

The size parameter in imx7_csi_alloc_dma_buf() is a signed int. This allows
large unsigned 32-bit sizeimage values (e.g., between 2 GB and 4 GB) to be
interpreted as negative, subverting the PAGE_ALIGN macro.

This seems to be reachable from userspace because imx7_csi_try_fmt() lacks
bounds checking for width and height in the IMX7_CSI_PAD_SINK case:

drivers/media/platform/nxp/imx7-media-csi.c:imx7_csi_try_fmt() {
    ...
    case IMX7_CSI_PAD_SINK:
        *cc = imx7_csi_find_mbus_format(sdformat->format.code);
    ...
}

This allows massive dimensions to bypass validation. When passed to
__imx7_csi_video_try_fmt(), the 32-bit multiplication overflows without
prior bounds checking on the total pixel volume:

drivers/media/platform/nxp/imx7-media-csi.c:__imx7_csi_video_try_fmt() {
    ...
    pixfmt->sizeimage = pixfmt->bytesperline * pixfmt->height;
    ...
}

If a user calls VIDIOC_S_FMT with large dimensions (e.g., width=32896,
height=65281, and a 16-bpp format), the product wraps around modulo 2^32,
producing a very small positive sizeimage, or a negative size when passed
as a signed int to imx7_csi_alloc_dma_buf().

As a result, a tiny buffer is allocated here, but the CSI hardware could
capture the massive frame and DMA up to 4 GB of data into it, seamlessly
crossing the buffer boundary.

>  	if (!buf->virt)
>  		return -ENOMEM;
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260903111836.1777265-1-hebaoquan@kylinos.cn?part=10