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SubjectRe: [PATCH] media: cx18, ivtv: do not dereference array before index check
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On Sat, 2013-01-05 at 14:11 -0500, Nickolai Zeldovich wrote:
> Move dereferencing of hw_devicenames[], hw_bus[] arrays until after
> checking that idx is within range.
>
> Signed-off-by: Nickolai Zeldovich <nickolai@csail.mit.edu>

Hi Nickolai,

My comments are in line below.

> ---
> drivers/media/pci/cx18/cx18-i2c.c | 10 +++++++---
> drivers/media/pci/ivtv/ivtv-i2c.c | 5 ++++-
> 2 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/pci/cx18/cx18-i2c.c b/drivers/media/pci/cx18/cx18-i2c.c
> index 4908eb7..d164239 100644
> --- a/drivers/media/pci/cx18/cx18-i2c.c
> +++ b/drivers/media/pci/cx18/cx18-i2c.c
> @@ -111,14 +111,18 @@ static int cx18_i2c_new_ir(struct cx18 *cx, struct i2c_adapter *adap, u32 hw,
> int cx18_i2c_register(struct cx18 *cx, unsigned idx)
> {
> struct v4l2_subdev *sd;
> - int bus = hw_bus[idx];
> - struct i2c_adapter *adap = &cx->i2c_adap[bus];
> - const char *type = hw_devicenames[idx];
> + int bus;
> + struct i2c_adapter *adap;
> + const char *type;
> u32 hw = 1 << idx;
>
> if (idx >= ARRAY_SIZE(hw_addrs))
> return -1;
>
> + bus = hw_bus[idx];
> + adap = &cx->i2c_adap[bus];
> + type = hw_devicenames[idx];
> +

It would be better to simply remove the "if (idx >= ARRAY_SIZE(...))"
check. That change would result in fewer lines of code instead of more
lines of code. It is statically provable that cx18_i2c_register() is
never called with a bad idx value.


> if (hw == CX18_HW_TUNER) {
> /* special tuner group handling */
> sd = v4l2_i2c_new_subdev(&cx->v4l2_dev,
> diff --git a/drivers/media/pci/ivtv/ivtv-i2c.c b/drivers/media/pci/ivtv/ivtv-i2c.c
> index 46e262b..c6af94c 100644
> --- a/drivers/media/pci/ivtv/ivtv-i2c.c
> +++ b/drivers/media/pci/ivtv/ivtv-i2c.c
> @@ -264,11 +264,14 @@ int ivtv_i2c_register(struct ivtv *itv, unsigned idx)
> {
> struct v4l2_subdev *sd;
> struct i2c_adapter *adap = &itv->i2c_adap;
> - const char *type = hw_devicenames[idx];
> + const char *type;
> u32 hw = 1 << idx;
>
> if (idx >= ARRAY_SIZE(hw_addrs))
> return -1;
> +
> + type = hw_devicenames[idx];
> +

It would be better to simply remove the "if (idx >= ARRAY_SIZE(...))"
check. That change would result in fewer lines of code instead of more
lines of code. It is statically provable that ivtv_i2c_register() is
never called with a bad idx value.

Regards,
Andy

> if (hw == IVTV_HW_TUNER) {
> /* special tuner handling */
> sd = v4l2_i2c_new_subdev(&itv->v4l2_dev, adap, type, 0,




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