linux-kernel - Re: [PATCHv2] media: videobuf2-dma-contig: fix bad kfree in vb2_dma_contig_clear_max_seg

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Date:   Thu, 28 May 2020 11:14:18 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Tomi Valkeinen <tomi.valkeinen@...com>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "# 4.0+" <stable@...r.kernel.org>
Subject: Re: [PATCHv2] media: videobuf2-dma-contig: fix bad kfree in vb2_dma_contig_clear_max_seg_size

On Wed, 27 May 2020 at 10:23, Tomi Valkeinen <tomi.valkeinen@...com> 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@...com>
> Fixes: 9495b7e92f71 ("driver core: platform: Initialize dma_parms for platform devices")
> Cc: stable@...r.kernel.org

Thanks for fixing this!

However, as I tried to point out in v1, don't you need to care about
drivers/media/platform/s5p-mfc/s5p_mfc.c, which allocates its own type
of struct device (non-platform). No?

Kind regards
Uffe


> ---
>
> 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@...iak.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;
>
> --
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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