linux-kernel - Re: [PATCH 1/2] SPI: Add SPI driver for Sunplus SP7021

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Message-ID: <20211114080209.GA9914@wunner.de>
Date:   Sun, 14 Nov 2021 09:02:09 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     "LH.Kuo" <lhjeff911@...il.com>
Cc:     p.zabel@...gutronix.de, broonie@...nel.org,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        dvorkin@...bo.com, qinjian@...lus1.com, wells.lu@...plus.com,
        "LH.Kuo" <lh.kuo@...plus.com>
Subject: Re: [PATCH 1/2] SPI: Add SPI driver for Sunplus SP7021

On Mon, Nov 01, 2021 at 02:18:44PM +0800, LH.Kuo wrote:
> +	if (mode == SPI_SLAVE)
> +		ctlr = spi_alloc_slave(&pdev->dev, sizeof(*pspim));
> +	else
> +		ctlr = spi_alloc_master(&pdev->dev, sizeof(*pspim));
> +	if (!ctlr)
> +		return -ENOMEM;

You need to use devm_spi_alloc_master() and devm_spi_alloc_slave() here
to avoid a use-after-free in pentagram_spi_controller_remove():

That's because spi_unregister_master() frees the spi_controller struct
and the adjacent pspim allocation and pentagram_spi_controller_remove()
accesses pspim afterwards.

The allocation is *not* freed by spi_unregister_master() if the devm_*
variants are used for allocation.  Rather, the allocation is freed only
after pentagram_spi_controller_remove() has finished.

> +free_alloc:
> +	spi_controller_put(ctlr);

This can be dropped if the devm_* variants are used for allocation.

> +	spi_unregister_master(pspim->ctlr);

Please use spi_unregister_controller() here.  (It could be a slave.)

Thanks,

Lukas