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Subject: Re: [PATCHv2] media: videobuf2-dma-contig: fix bad kfree in
 vb2_dma_contig_clear_max_seg_size
To:     Tomi Valkeinen <tomi.valkeinen@ti.com>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, stable@vger.kernel.org
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-ID: <8b53b12f-2971-8b92-9617-a73d0b9d312f@samsung.com>
Date:   Thu, 28 May 2020 07:48:20 +0200
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On 27.05.2020 10:23, Tomi Valkeinen wrote:
> Commit 9495b7e92f716ab2bd6814fab5e97ab4a39adfdd ("driver core: platform:
> Initialize dma_parms for platform devices") in v5.7-rc5 causes
> vb2_dma_contig_clear_max_seg_size() to kfree memory that was not
> allocated by vb2_dma_contig_set_max_seg_size().
>
> The assumption in vb2_dma_contig_set_max_seg_size() seems to be that
> dev->dma_parms is always NULL when the driver is probed, and the case
> where dev->dma_parms has bee initialized by someone else than the driver
> (by calling vb2_dma_contig_set_max_seg_size) will cause a failure.
>
> All the current users of these functions are platform devices, which now
> always have dma_parms set by the driver core. To fix the issue for v5.7,
> make vb2_dma_contig_set_max_seg_size() return an error if dma_parms is
> NULL to be on the safe side, and remove the kfree code from
> vb2_dma_contig_clear_max_seg_size().
>
> For v5.8 we should remove the two functions and move the
> dma_set_max_seg_size() calls into the drivers.
>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Fixes: 9495b7e92f71 ("driver core: platform: Initialize dma_parms for platform devices")
> Cc: stable@vger.kernel.org
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>
> Changes in v2:
> * vb2_dma_contig_clear_max_seg_size to empty static inline
> * Added cc: stable and fixes tag
>
>   .../common/videobuf2/videobuf2-dma-contig.c   | 20 ++-----------------
>   include/media/videobuf2-dma-contig.h          |  2 +-
>   2 files changed, 3 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> index d3a3ee5b597b..f4b4a7c135eb 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> @@ -726,9 +726,8 @@ EXPORT_SYMBOL_GPL(vb2_dma_contig_memops);
>   int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size)
>   {
>   	if (!dev->dma_parms) {
> -		dev->dma_parms = kzalloc(sizeof(*dev->dma_parms), GFP_KERNEL);
> -		if (!dev->dma_parms)
> -			return -ENOMEM;
> +		dev_err(dev, "Failed to set max_seg_size: dma_parms is NULL\n");
> +		return -ENODEV;
>   	}
>   	if (dma_get_max_seg_size(dev) < size)
>   		return dma_set_max_seg_size(dev, size);
> @@ -737,21 +736,6 @@ int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size)
>   }
>   EXPORT_SYMBOL_GPL(vb2_dma_contig_set_max_seg_size);
>   
> -/*
> - * vb2_dma_contig_clear_max_seg_size() - release resources for DMA parameters
> - * @dev:	device for configuring DMA parameters
> - *
> - * This function releases resources allocated to configure DMA parameters
> - * (see vb2_dma_contig_set_max_seg_size() function). It should be called from
> - * device drivers on driver remove.
> - */
> -void vb2_dma_contig_clear_max_seg_size(struct device *dev)
> -{
> -	kfree(dev->dma_parms);
> -	dev->dma_parms = NULL;
> -}
> -EXPORT_SYMBOL_GPL(vb2_dma_contig_clear_max_seg_size);
> -
>   MODULE_DESCRIPTION("DMA-contig memory handling routines for videobuf2");
>   MODULE_AUTHOR("Pawel Osciak <pawel@osciak.com>");
>   MODULE_LICENSE("GPL");
> diff --git a/include/media/videobuf2-dma-contig.h b/include/media/videobuf2-dma-contig.h
> index 5604818d137e..5be313cbf7d7 100644
> --- a/include/media/videobuf2-dma-contig.h
> +++ b/include/media/videobuf2-dma-contig.h
> @@ -25,7 +25,7 @@ vb2_dma_contig_plane_dma_addr(struct vb2_buffer *vb, unsigned int plane_no)
>   }
>   
>   int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size);
> -void vb2_dma_contig_clear_max_seg_size(struct device *dev);
> +static inline void vb2_dma_contig_clear_max_seg_size(struct device *dev) { }
>   
>   extern const struct vb2_mem_ops vb2_dma_contig_memops;
>   

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland