linux-kernel - Re: [PATCH] spi: stm32: drop devres version of spi_register

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Date:   Tue, 16 Mar 2021 22:17:44 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Alain Volmat <alain.volmat@...s.st.com>
Cc:     broonie@...nel.org, amelie.delaunay@...s.st.com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...s.st.com,
        linux-spi@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        fabrice.gasnier@...s.st.com, antonio.borneo@...s.st.com
Subject: Re: [PATCH] spi: stm32: drop devres version of spi_register_master

On Fri, Mar 12, 2021 at 11:34:46AM +0100, Alain Volmat wrote:
> --- a/drivers/spi/spi-stm32.c
> +++ b/drivers/spi/spi-stm32.c
> @@ -1960,6 +1960,7 @@ static int stm32_spi_remove(struct platform_device *pdev)
>  	struct spi_master *master = platform_get_drvdata(pdev);
>  	struct stm32_spi *spi = spi_master_get_devdata(master);
>  
> +	spi_unregister_master(master);
>  	spi->cfg->disable(spi);
>  
>  	if (master->dma_tx)

This introduces a use-after-free because spi_unregister_master()
drops the last reference on the spi_master allocation (which includes
the struct stm32_spi), causing it to be freed, yet the stm32_spi
struct is accessed afterwards.

You need to convert the driver to devm_spi_alloc_master() to
fix the use-after-free.  See commit 6cfd39e212de for an example.

Thanks,

Lukas