linux-kernel - Re: [PATCH v2] media: cx18, ivtv: eliminate unnecessary array index checks

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Message-ID: <041715b8-e711-4c63-a123-296c5b674edf@email.android.com>
Date:	Sun, 06 Jan 2013 21:08:39 -0500
From:	Andy Walls <awalls@...metrocast.net>
To:	Nickolai Zeldovich <nickolai@...il.mit.edu>,
	Mauro Carvalho Chehab <mchehab@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH v2] media: cx18, ivtv: eliminate unnecessary array index checks

Nickolai Zeldovich <nickolai@...il.mit.edu> wrote:

>The idx values passed to cx18_i2c_register() and ivtv_i2c_register()
>by cx18_init_subdevs() and ivtv_load_and_init_modules() respectively
>are always in-range, based on how the hw_all bitmask is populated.
>Previously, the checks were already ineffective because arrays were
>being dereferenced using the index before the check.
>
>Signed-off-by: Nickolai Zeldovich <nickolai@...il.mit.edu>
>---
>Thanks to Andy Walls for suggesting that instead of moving the checks
>before array dereference, a better fix is to remove the checks
>altogether,
>since they are superfluous.
>
> drivers/media/pci/cx18/cx18-i2c.c |    3 ---
> drivers/media/pci/ivtv/ivtv-i2c.c |    2 --
> 2 files changed, 5 deletions(-)
>
>diff --git a/drivers/media/pci/cx18/cx18-i2c.c
>b/drivers/media/pci/cx18/cx18-i2c.c
>index 4908eb7..ccb1d15 100644
>--- a/drivers/media/pci/cx18/cx18-i2c.c
>+++ b/drivers/media/pci/cx18/cx18-i2c.c
>@@ -116,9 +116,6 @@ int cx18_i2c_register(struct cx18 *cx, unsigned
>idx)
> 	const char *type = hw_devicenames[idx];
> 	u32 hw = 1 << idx;
> 
>-	if (idx >= ARRAY_SIZE(hw_addrs))
>-		return -1;
>-
> 	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..bc984af 100644
>--- a/drivers/media/pci/ivtv/ivtv-i2c.c
>+++ b/drivers/media/pci/ivtv/ivtv-i2c.c
>@@ -267,8 +267,6 @@ int ivtv_i2c_register(struct ivtv *itv, unsigned
>idx)
> 	const char *type = hw_devicenames[idx];
> 	u32 hw = 1 << idx;
> 
>-	if (idx >= ARRAY_SIZE(hw_addrs))
>-		return -1;
> 	if (hw == IVTV_HW_TUNER) {
> 		/* special tuner handling */
> 		sd = v4l2_i2c_new_subdev(&itv->v4l2_dev, adap, type, 0,
>-- 
>1.7.10.4

Acked-by: Andy Walls <awalls@...metrocast.net>
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