linux-kernel - Re: [PATCH v3 1/3] spi: spidev: create spidev device for all spi slaves.

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Date:	Mon, 18 Jul 2016 23:59:52 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] spi: spidev: create spidev device for all spi
 slaves.

On Tue, Jul 19, 2016 at 12:35:40AM +0200, Michal Suchanek wrote:

>  config SPI_SPIDEV
> -	tristate "User mode SPI device driver support"
> +	bool "User mode SPI device driver support"

This is a step back, it would require spidev to be built in.

> -	spin_lock_irq(&spidev->spi_lock);
> -	spi = spi_dev_get(spidev->spi);
> -	spin_unlock_irq(&spidev->spi_lock);
> +	spi = filp->private_data;
> +	spi = spi_dev_get(spi);

All this refactoring to move spidev about should've been a separate
patch, it's hard to find the actual content in here.

> -	mutex_lock(&device_list_lock);
> +	dev = bus_find_device(&spi_bus_type, NULL, (void *) inode->i_rdev,
> +			      spidev_devt_match);

...

> -			dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
> +	spi = to_spi_device(dev);
> +
> +	mutex_lock(&spi->buf_lock);
> +	spin_lock_irq(&spi->spidev_lock);
> +	spi->spidev_users++;
> +	spin_unlock_irq(&spi->spidev_lock);

This is broken, it will unconditionally create a spidev for any chip
select regardless of if there's any actual hardware there and (even more
importantly) regardless if that hardware is actually a SPI device.  This
is not safe, especially given some of the ideas people seem to have for
userspaces.

I am getting completely fed up of saying this, it's not OK to just
expose pins to userspace when we have no idea what they are connected
to.

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