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 11:24:17 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Tomi Valkeinen <tomi.valkeinen@...com>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        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

Hi Ulf,

On 28.05.2020 11:14, Ulf Hansson wrote:
> 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?

I will send a patch for the S5P MFC driver separately. It is not so 
critical, because the mentioned 2port memory case is not used on any 
board with the default exynos_defconfig from mainline. On Exynos4-based 
boards it is only used when IOMMU is disabled. It is mainly for 
S5PV210/S5PC110 boards, which are still not fully functional after 
conversion to device-tree.

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