Re: [PATCH] [media] cx18: introduce a helper function to avoid array overrun

Re: [PATCH] [media] cx18: introduce a helper function to avoid array overrun

[Hans Verkuil]

Also CC to linux-media and Andy Walls who maintains this driver.

Regards,

	Hans

On 01/06/14 16:07, Ethan Zhao wrote:
> cx18_i2c_register() is called in cx18_init_subdevs() with index
> greater than length of hw_bus array, that will cause array overrun,
> introduce a helper cx18_get_max_bus_num() to avoid it.
> 
> V2: fix a typo and use ARRAY_SIZE macro
> 
> Signed-off-by: Ethan Zhao <ethan.kernel@gmail.com>
> ---
>  drivers/media/pci/cx18/cx18-driver.c | 2 +-
>  drivers/media/pci/cx18/cx18-i2c.c    | 5 +++++
>  drivers/media/pci/cx18/cx18-i2c.h    | 1 +
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/pci/cx18/cx18-driver.c b/drivers/media/pci/cx18/cx18-driver.c
> index 6386ced..dadcd4a 100644
> --- a/drivers/media/pci/cx18/cx18-driver.c
> +++ b/drivers/media/pci/cx18/cx18-driver.c
> @@ -856,7 +856,7 @@ static void cx18_init_subdevs(struct cx18 *cx)
>  	u32 device;
>  	int i;
>  
> -	for (i = 0, device = 1; i < 32; i++, device <<= 1) {
> +	for (i = 0, device = 1; i < cx18_get_max_bus_num(); i++, device <<= 1) {
>  
>  		if (!(device & hw))
>  			continue;
> diff --git a/drivers/media/pci/cx18/cx18-i2c.c b/drivers/media/pci/cx18/cx18-i2c.c
> index 4af8cd6..1a7b49b 100644
> --- a/drivers/media/pci/cx18/cx18-i2c.c
> +++ b/drivers/media/pci/cx18/cx18-i2c.c
> @@ -108,6 +108,11 @@ static int cx18_i2c_new_ir(struct cx18 *cx, struct i2c_adapter *adap, u32 hw,
>  	       -1 : 0;
>  }
>  
> +int cx18_get_max_bus_num(void)
> +{
> +	return ARRAY_SIZE(hw_bus);
> +}
> +
>  int cx18_i2c_register(struct cx18 *cx, unsigned idx)
>  {
>  	struct v4l2_subdev *sd;
> diff --git a/drivers/media/pci/cx18/cx18-i2c.h b/drivers/media/pci/cx18/cx18-i2c.h
> index 1180fdc..6f2ceb5 100644
> --- a/drivers/media/pci/cx18/cx18-i2c.h
> +++ b/drivers/media/pci/cx18/cx18-i2c.h
> @@ -21,6 +21,7 @@
>   *  02111-1307  USA
>   */
>  
> +int cx18_get_max_bus_num(void);
>  int cx18_i2c_register(struct cx18 *cx, unsigned idx);
>  struct v4l2_subdev *cx18_find_hw(struct cx18 *cx, u32 hw);
>  
> 

Re: [PATCH] [media] cx18: introduce a helper function to avoid array overrun

[Andy Walls]

On Fri, 2014-01-10 at 14:06 +0100, Hans Verkuil wrote:
> Also CC to linux-media and Andy Walls who maintains this driver.
> 
> Regards,
> 
> 	Hans
> 
> On 01/06/14 16:07, Ethan Zhao wrote:
> > cx18_i2c_register() is called in cx18_init_subdevs() with index
> > greater than length of hw_bus array, that will cause array overrun,
> > introduce a helper cx18_get_max_bus_num() to avoid it.
> > 
> > V2: fix a typo and use ARRAY_SIZE macro
> > 
> > Signed-off-by: Ethan Zhao <ethan.kernel@gmail.com>

Hi Ethan,

There is no need for this change.  See below.

> > ---
> >  drivers/media/pci/cx18/cx18-driver.c | 2 +-
> >  drivers/media/pci/cx18/cx18-i2c.c    | 5 +++++
> >  drivers/media/pci/cx18/cx18-i2c.h    | 1 +
> >  3 files changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/pci/cx18/cx18-driver.c b/drivers/media/pci/cx18/cx18-driver.c
> > index 6386ced..dadcd4a 100644
> > --- a/drivers/media/pci/cx18/cx18-driver.c
> > +++ b/drivers/media/pci/cx18/cx18-driver.c
> > @@ -856,7 +856,7 @@ static void cx18_init_subdevs(struct cx18 *cx)
> >  	u32 device;
> >  	int i;
> >  
> > -	for (i = 0, device = 1; i < 32; i++, device <<= 1) {
> > +	for (i = 0, device = 1; i < cx18_get_max_bus_num(); i++, device <<= 1) {
> >  
> >  		if (!(device & hw))
> >  			continue;

This check of "!(device & hw)" already does the bounds check.  Card
specific, I2C device presence flags are statically compiled into the
driver in cx18-cards.c and are used in this check.

The ivtv driver does the same sort of check in
ivtv-driver.c:ivtv_load_and_init_modules().

Both the cx18 and ivtv drivers are very mature, so I don't want any
unecessary code churn in them to address non-problems.

Regards,
Andy

> > diff --git a/drivers/media/pci/cx18/cx18-i2c.c b/drivers/media/pci/cx18/cx18-i2c.c
> > index 4af8cd6..1a7b49b 100644
> > --- a/drivers/media/pci/cx18/cx18-i2c.c
> > +++ b/drivers/media/pci/cx18/cx18-i2c.c
> > @@ -108,6 +108,11 @@ static int cx18_i2c_new_ir(struct cx18 *cx, struct i2c_adapter *adap, u32 hw,
> >  	       -1 : 0;
> >  }
> >  
> > +int cx18_get_max_bus_num(void)
> > +{
> > +	return ARRAY_SIZE(hw_bus);
> > +}
> > +
> >  int cx18_i2c_register(struct cx18 *cx, unsigned idx)
> >  {
> >  	struct v4l2_subdev *sd;
> > diff --git a/drivers/media/pci/cx18/cx18-i2c.h b/drivers/media/pci/cx18/cx18-i2c.h
> > index 1180fdc..6f2ceb5 100644
> > --- a/drivers/media/pci/cx18/cx18-i2c.h
> > +++ b/drivers/media/pci/cx18/cx18-i2c.h
> > @@ -21,6 +21,7 @@
> >   *  02111-1307  USA
> >   */
> >  
> > +int cx18_get_max_bus_num(void);
> >  int cx18_i2c_register(struct cx18 *cx, unsigned idx);
> >  struct v4l2_subdev *cx18_find_hw(struct cx18 *cx, u32 hw);
> >  
> >