[PATCH] Usb: host - Fix possible NULL derefrence.

[PATCH] Usb: host - Fix possible NULL derefrence.

[Shailendra Verma]

of_device_get_match_data could return NULL, and so can cause
a NULL pointer dereference later.

Signed-off-by: Shailendra Verma <shailendra.v@samsung.com>
---
 drivers/usb/host/xhci-tegra.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/host/xhci-tegra.c b/drivers/usb/host/xhci-tegra.c
index a59fafb..890c778 100644
--- a/drivers/usb/host/xhci-tegra.c
+++ b/drivers/usb/host/xhci-tegra.c
@@ -903,6 +903,10 @@ static int tegra_xusb_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	tegra->soc = of_device_get_match_data(&pdev->dev);
+	if (!tegra->soc) {
+		dev_err(&pdev->dev, "no device match found\n");
+		return -ENODEV;
+	}
 	mutex_init(&tegra->lock);
 	tegra->dev = &pdev->dev;
 
-- 
1.7.9.5

Re: [PATCH] Usb: host - Fix possible NULL derefrence.

[Greg Kroah-Hartman]

On Mon, Jan 30, 2017 at 10:36:29AM +0530, Shailendra Verma wrote:
> of_device_get_match_data could return NULL, and so can cause
> a NULL pointer dereference later.
> 
> Signed-off-by: Shailendra Verma <shailendra.v@samsung.com>
> ---
>  drivers/usb/host/xhci-tegra.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-tegra.c b/drivers/usb/host/xhci-tegra.c
> index a59fafb..890c778 100644
> --- a/drivers/usb/host/xhci-tegra.c
> +++ b/drivers/usb/host/xhci-tegra.c
> @@ -903,6 +903,10 @@ static int tegra_xusb_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  
>  	tegra->soc = of_device_get_match_data(&pdev->dev);
> +	if (!tegra->soc) {

How would the driver be loaded and the probe function called if this
returns NULL?

Is this ever possible?

thanks,

greg k-h

Re: [PATCH] Usb: host - Fix possible NULL derefrence.

[Thierry Reding]

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On Mon, Jan 30, 2017 at 07:45:21AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Jan 30, 2017 at 10:36:29AM +0530, Shailendra Verma wrote:
> > of_device_get_match_data could return NULL, and so can cause
> > a NULL pointer dereference later.
> > 
> > Signed-off-by: Shailendra Verma <shailendra.v@samsung.com>
> > ---
> >  drivers/usb/host/xhci-tegra.c |    4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/usb/host/xhci-tegra.c b/drivers/usb/host/xhci-tegra.c
> > index a59fafb..890c778 100644
> > --- a/drivers/usb/host/xhci-tegra.c
> > +++ b/drivers/usb/host/xhci-tegra.c
> > @@ -903,6 +903,10 @@ static int tegra_xusb_probe(struct platform_device *pdev)
> >  		return -ENOMEM;
> >  
> >  	tegra->soc = of_device_get_match_data(&pdev->dev);
> > +	if (!tegra->soc) {
> 
> How would the driver be loaded and the probe function called if this
> returns NULL?
> 
> Is this ever possible?

No, it isn't. I've been NAK'ing this kind of patch for a while now.
There are two variants of this patch going about:

  1) checking the return value of of_match_device()
  2) checking the return value of of_device_get_match_data()

The same may also apply to of_match_node(), but I haven't seen that used
very much lately.

For of_match_device() the problem could technically occur if used in non
OF setups, because the device could be instantiated by hand in board
setup code. Tegra has been OF-only for a couple of years now, so there
is no way this can happen today.

of_device_get_match_data() is somewhat more complicated because it could
still return NULL if the OF table entry had its .data field set to NULL.
However in all drivers that I know that would be considered a bug, so
might as well let things crash at this point to make it immediately
obvious.

I had once been tempted to write a checkpatch rule for this, but I'm not
sure it's as easy as just warning if there's a check, because there are
some legitimate cases, even if they're very rare.

Thierry

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Re: [PATCH] Usb: host - Fix possible NULL derefrence.

[Greg Kroah-Hartman]

On Mon, Jan 30, 2017 at 08:03:23AM +0100, Thierry Reding wrote:
> On Mon, Jan 30, 2017 at 07:45:21AM +0100, Greg Kroah-Hartman wrote:
> > On Mon, Jan 30, 2017 at 10:36:29AM +0530, Shailendra Verma wrote:
> > > of_device_get_match_data could return NULL, and so can cause
> > > a NULL pointer dereference later.
> > > 
> > > Signed-off-by: Shailendra Verma <shailendra.v@samsung.com>
> > > ---
> > >  drivers/usb/host/xhci-tegra.c |    4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/usb/host/xhci-tegra.c b/drivers/usb/host/xhci-tegra.c
> > > index a59fafb..890c778 100644
> > > --- a/drivers/usb/host/xhci-tegra.c
> > > +++ b/drivers/usb/host/xhci-tegra.c
> > > @@ -903,6 +903,10 @@ static int tegra_xusb_probe(struct platform_device *pdev)
> > >  		return -ENOMEM;
> > >  
> > >  	tegra->soc = of_device_get_match_data(&pdev->dev);
> > > +	if (!tegra->soc) {
> > 
> > How would the driver be loaded and the probe function called if this
> > returns NULL?
> > 
> > Is this ever possible?
> 
> No, it isn't. I've been NAK'ing this kind of patch for a while now.
> There are two variants of this patch going about:
> 
>   1) checking the return value of of_match_device()
>   2) checking the return value of of_device_get_match_data()
> 
> The same may also apply to of_match_node(), but I haven't seen that used
> very much lately.
> 
> For of_match_device() the problem could technically occur if used in non
> OF setups, because the device could be instantiated by hand in board
> setup code. Tegra has been OF-only for a couple of years now, so there
> is no way this can happen today.
> 
> of_device_get_match_data() is somewhat more complicated because it could
> still return NULL if the OF table entry had its .data field set to NULL.
> However in all drivers that I know that would be considered a bug, so
> might as well let things crash at this point to make it immediately
> obvious.
> 
> I had once been tempted to write a checkpatch rule for this, but I'm not
> sure it's as easy as just warning if there's a check, because there are
> some legitimate cases, even if they're very rare.

Thanks for the info, patch is now dropped.

Shailendra, please be more careful.

greg k-h