linux-kernel - Re: [PATCH] tpm: fix potential NULL pointer access in tpm_del_char

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Message-ID: <20210924142032.GY3544071@ziepe.ca>
Date:   Fri, 24 Sep 2021 11:20:32 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     Jarkko Sakkinen <jarkko@...nel.org>, peterhuewe@....de,
        p.rosenberger@...bus.com, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] tpm: fix potential NULL pointer access in
 tpm_del_char_device()

On Fri, Sep 24, 2021 at 04:17:52PM +0200, Lino Sanfilippo wrote:
> On 24.09.21 at 15:33, Jason Gunthorpe wrote:
> > On Fri, Sep 24, 2021 at 03:29:46PM +0200, Lino Sanfilippo wrote:
> >
> >> So this bug is triggered when the bcm2835 drivers shutdown() function is called since this
> >> driver does something quite unusual: it unregisters the spi controller in its shutdown()
> >> handler.
> >
> > This seems wrong
> >
> > Jason
> >
> 
> 
> Unregistering the SPI controller during shutdown is only a side-effect of calling
> bcm2835_spi_remove() in the shutdown handler:
> 
> static void bcm2835_spi_shutdown(struct platform_device *pdev)
> {
> 	int ret;
> 
> 	ret = bcm2835_spi_remove(pdev);
> 	if (ret)
> 		dev_err(&pdev->dev, "failed to shutdown\n");
> }

That's wrong, the shutdown handler is only supposed to make the HW
stop doing DMA and interrupts so we can have a clean transition to
kexec/etc

It should not be manipulating other state.

Jason