Re: [PATCH] of: dma_configure: Free old DMA map range

[Rob Herring <robh@kernel.org>]

On Fri, Feb 04, 2022 at 09:45:56AM +0100, Mårten Lindahl wrote:
> When unbinding/binding a driver with DMA mapped memory, the DMA map is
> not freed when the driver is reloaded. This leads to a memory leak when
> the DMA map is overwritten when reprobing the driver.
> 
> This can be reproduced with a platform driver having a dma-range:
> 
> dummy {
> 	...
> 	#address-cells = <0x2>;
> 	#size-cells = <0x2>;
> 	ranges;
> 	dma-ranges = <...>;
> 	...
> };
> 
> and then unbinding/binding it:
> 
> ~# echo soc:dummy >/sys/bus/platform/drivers/<driver>/unbind
> 
> DMA map object 0xffffff800b0ae540 still being held by &pdev->dev
> 
> ~# echo soc:dummy >/sys/bus/platform/drivers/<driver>/bind
> ~# echo scan > /sys/kernel/debug/kmemleak
> ~# cat /sys/kernel/debug/kmemleak
> unreferenced object 0xffffff800b0ae540 (size 64):
>   comm "sh", pid 833, jiffies 4295174550 (age 2535.352s)
>   hex dump (first 32 bytes):
>     00 00 00 80 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 80 00 00 00 00 00 00 00 80 00 00 00 00  ................
>   backtrace:
>     [<ffffffefd1694708>] create_object.isra.0+0x108/0x344
>     [<ffffffefd1d1a850>] kmemleak_alloc+0x8c/0xd0
>     [<ffffffefd167e2d0>] __kmalloc+0x440/0x6f0
>     [<ffffffefd1a960a4>] of_dma_get_range+0x124/0x220
>     [<ffffffefd1a8ce90>] of_dma_configure_id+0x40/0x2d0
>     [<ffffffefd198b68c>] platform_dma_configure+0x5c/0xa4
>     [<ffffffefd198846c>] really_probe+0x8c/0x514
>     [<ffffffefd1988990>] __driver_probe_device+0x9c/0x19c
>     [<ffffffefd1988cd8>] device_driver_attach+0x54/0xbc
>     [<ffffffefd1986634>] bind_store+0xc4/0x120
>     [<ffffffefd19856e0>] drv_attr_store+0x30/0x44
>     [<ffffffefd173c9b0>] sysfs_kf_write+0x50/0x60
>     [<ffffffefd173c1c4>] kernfs_fop_write_iter+0x124/0x1b4
>     [<ffffffefd16a013c>] new_sync_write+0xdc/0x160
>     [<ffffffefd16a256c>] vfs_write+0x23c/0x2a0
>     [<ffffffefd16a2758>] ksys_write+0x64/0xec
> 
> Prevent overwriting the dma_range_map by freeing it before saving the
> new map.
> 
> Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
> ---
>  drivers/of/device.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index 874f031442dc..a67703d09bfd 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -156,6 +156,12 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
>  			kfree(map);
>  			return -EINVAL;
>  		}
> +
> +		/*
> +		 * Since we are about to set a new range map we should make sure we
> +		 * do not overwrite any existing one without having freed it first.
> +		 */
> +		kfree(dev->dma_range_map);


The map can't change, can't we just reuse the existing map. Or just bail 
early? I suppose the driver could have modified the dma masks. Or the 
IOMMU config could have changed.

Rob