linux-kernel - RE: [PATCH 2/2] tty: serial: fsl_lpuart: fix the potential bug of dereference null return value

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Date:   Mon, 26 Apr 2021 12:09:46 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Fabio Estevam <festevam@...il.com>
CC:     Greg KH <gregkh@...uxfoundation.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 2/2] tty: serial: fsl_lpuart: fix the potential bug of
 dereference null return value

Hi Fabio,

> Hi Sherry,
> 
> On Mon, Apr 26, 2021 at 8:39 AM Sherry Sun <sherry.sun@....com> wrote:
> 
> > > > +   if (!sdata)
> > > > +           return -ENODEV;
> > >
> > > How can sdata be NULL?
> >
> > Is it possible that a case forgot to set sdata? Then the value will be NULL,
> such as { .compatible = "fsl,imx8qxp-lpuart",  }.
> > So I added the patch to avoid the kernel crash when run to sdata->reg_off
> directly. But I am not sure does it make sense.
> 
> sdata comes directly from of_device_get_match_data().
> 
> This driver only runs on DT platforms and the only way of being probed is
> when a compatible string matches, so it is not possible that sdata can be
> NULL.

Thanks for your reply.
I guess you mean the of_match_table will not be NULL since it contains compatible, right?
But for the lpuart data -- struct lpuart_soc_data, won’t it meet the NULL case? such as { .compatible = "fsl,imx8qxp-lpuart",  }.
Here of_device_id won’t be NULL, but lpuart_soc_data Is NULL.

Best regards
Sherry