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

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Date:   Thu, 18 Mar 2021 08:22:38 +0100
From:   Alain Volmat <alain.volmat@...s.st.com>
To:     Lukas Wunner <lukas@...ner.de>
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

Hi Lukas,

On Tue, Mar 16, 2021 at 10:17:44PM +0100, Lukas Wunner wrote:
> 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.

Indeed. Thanks. I've fixed that and will post it.

> 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