Re: [PATCHv2 19/29] tuners: Don't use dynamic static allocation

[Hans Verkuil <hverkuil@xs4all.nl>]

Hi Mauro,

I'll review this series more carefully on Monday, but for now I want to make
a suggestion for the array checks:

On 11/02/2013 02:31 PM, Mauro Carvalho Chehab wrote:
> Dynamic static allocation is evil, as Kernel stack is too low, and
> compilation complains about it on some archs:
> 
> 	drivers/media/tuners/e4000.c:50:1: warning: 'e4000_wr_regs' uses dynamic stack allocation [enabled by default]
> 	drivers/media/tuners/e4000.c:83:1: warning: 'e4000_rd_regs' uses dynamic stack allocation [enabled by default]
> 	drivers/media/tuners/fc2580.c:66:1: warning: 'fc2580_wr_regs.constprop.1' uses dynamic stack allocation [enabled by default]
> 	drivers/media/tuners/fc2580.c:98:1: warning: 'fc2580_rd_regs.constprop.0' uses dynamic stack allocation [enabled by default]
> 	drivers/media/tuners/tda18212.c:57:1: warning: 'tda18212_wr_regs' uses dynamic stack allocation [enabled by default]
> 	drivers/media/tuners/tda18212.c:90:1: warning: 'tda18212_rd_regs.constprop.0' uses dynamic stack allocation [enabled by default]
> 	drivers/media/tuners/tda18218.c:60:1: warning: 'tda18218_wr_regs' uses dynamic stack allocation [enabled by default]
> 	drivers/media/tuners/tda18218.c:92:1: warning: 'tda18218_rd_regs.constprop.0' uses dynamic stack allocation [enabled by default]
> 
> Instead, let's enforce a limit for the buffer. Considering that I2C
> transfers are generally limited, and that devices used on USB has a
> max data length of 80, it seem safe to use 80 as the hard limit for all
> those devices. On most cases, the limit is a way lower than that, but
> 80 is small enough to not affect the Kernel stack, and it is a no brain
> limit, as using smaller ones would require to either carefully each
> driver or to take a look on each datasheet.
> 
> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
> Cc: Antti Palosaari <crope@iki.fi>
> ---
>  drivers/media/tuners/e4000.c    | 18 ++++++++++++++++--
>  drivers/media/tuners/fc2580.c   | 18 ++++++++++++++++--
>  drivers/media/tuners/tda18212.c | 18 ++++++++++++++++--
>  drivers/media/tuners/tda18218.c | 18 ++++++++++++++++--
>  4 files changed, 64 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/tuners/e4000.c b/drivers/media/tuners/e4000.c
> index ad9309da4a91..235e90251609 100644
> --- a/drivers/media/tuners/e4000.c
> +++ b/drivers/media/tuners/e4000.c
> @@ -24,7 +24,7 @@
>  static int e4000_wr_regs(struct e4000_priv *priv, u8 reg, u8 *val, int len)
>  {
>  	int ret;
> -	u8 buf[1 + len];
> +	u8 buf[80];
>  	struct i2c_msg msg[1] = {
>  		{
>  			.addr = priv->cfg->i2c_addr,
> @@ -34,6 +34,13 @@ static int e4000_wr_regs(struct e4000_priv *priv, u8 reg, u8 *val, int len)
>  		}
>  	};
>  
> +	if (1 + len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c wr reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +

I think this can be greatly simplified to:

	if (WARN_ON(len + 1 > sizeof(buf))
		return -EREMOTEIO;

This should really never happen, and it is a clear driver bug if it does. WARN_ON
does the job IMHO. I also don't like the EREMOTEIO error: it has nothing to do with
an I/O problem. Wouldn't EMSGSIZE be much better here?

Ditto for all the similar situations in the patch series.

Regards,

	Hans

>  	buf[0] = reg;
>  	memcpy(&buf[1], val, len);
>  
> @@ -53,7 +60,7 @@ static int e4000_wr_regs(struct e4000_priv *priv, u8 reg, u8 *val, int len)
>  static int e4000_rd_regs(struct e4000_priv *priv, u8 reg, u8 *val, int len)
>  {
>  	int ret;
> -	u8 buf[len];
> +	u8 buf[80];
>  	struct i2c_msg msg[2] = {
>  		{
>  			.addr = priv->cfg->i2c_addr,
> @@ -68,6 +75,13 @@ static int e4000_rd_regs(struct e4000_priv *priv, u8 reg, u8 *val, int len)
>  		}
>  	};
>  
> +	if (len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c rd reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +
>  	ret = i2c_transfer(priv->i2c, msg, 2);
>  	if (ret == 2) {
>  		memcpy(val, buf, len);
> diff --git a/drivers/media/tuners/fc2580.c b/drivers/media/tuners/fc2580.c
> index 81f38aae9c66..e27bf5be311d 100644
> --- a/drivers/media/tuners/fc2580.c
> +++ b/drivers/media/tuners/fc2580.c
> @@ -41,7 +41,7 @@
>  static int fc2580_wr_regs(struct fc2580_priv *priv, u8 reg, u8 *val, int len)
>  {
>  	int ret;
> -	u8 buf[1 + len];
> +	u8 buf[80];
>  	struct i2c_msg msg[1] = {
>  		{
>  			.addr = priv->cfg->i2c_addr,
> @@ -51,6 +51,13 @@ static int fc2580_wr_regs(struct fc2580_priv *priv, u8 reg, u8 *val, int len)
>  		}
>  	};
>  
> +	if (1 + len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c wr reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +
>  	buf[0] = reg;
>  	memcpy(&buf[1], val, len);
>  
> @@ -69,7 +76,7 @@ static int fc2580_wr_regs(struct fc2580_priv *priv, u8 reg, u8 *val, int len)
>  static int fc2580_rd_regs(struct fc2580_priv *priv, u8 reg, u8 *val, int len)
>  {
>  	int ret;
> -	u8 buf[len];
> +	u8 buf[80];
>  	struct i2c_msg msg[2] = {
>  		{
>  			.addr = priv->cfg->i2c_addr,
> @@ -84,6 +91,13 @@ static int fc2580_rd_regs(struct fc2580_priv *priv, u8 reg, u8 *val, int len)
>  		}
>  	};
>  
> +	if (len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c rd reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +
>  	ret = i2c_transfer(priv->i2c, msg, 2);
>  	if (ret == 2) {
>  		memcpy(val, buf, len);
> diff --git a/drivers/media/tuners/tda18212.c b/drivers/media/tuners/tda18212.c
> index e4a84ee231cf..765b9f9d4bc6 100644
> --- a/drivers/media/tuners/tda18212.c
> +++ b/drivers/media/tuners/tda18212.c
> @@ -32,7 +32,7 @@ static int tda18212_wr_regs(struct tda18212_priv *priv, u8 reg, u8 *val,
>  	int len)
>  {
>  	int ret;
> -	u8 buf[len+1];
> +	u8 buf[80];
>  	struct i2c_msg msg[1] = {
>  		{
>  			.addr = priv->cfg->i2c_address,
> @@ -42,6 +42,13 @@ static int tda18212_wr_regs(struct tda18212_priv *priv, u8 reg, u8 *val,
>  		}
>  	};
>  
> +	if (1 + len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c wr reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +
>  	buf[0] = reg;
>  	memcpy(&buf[1], val, len);
>  
> @@ -61,7 +68,7 @@ static int tda18212_rd_regs(struct tda18212_priv *priv, u8 reg, u8 *val,
>  	int len)
>  {
>  	int ret;
> -	u8 buf[len];
> +	u8 buf[80];
>  	struct i2c_msg msg[2] = {
>  		{
>  			.addr = priv->cfg->i2c_address,
> @@ -76,6 +83,13 @@ static int tda18212_rd_regs(struct tda18212_priv *priv, u8 reg, u8 *val,
>  		}
>  	};
>  
> +	if (len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c rd reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +
>  	ret = i2c_transfer(priv->i2c, msg, 2);
>  	if (ret == 2) {
>  		memcpy(val, buf, len);
> diff --git a/drivers/media/tuners/tda18218.c b/drivers/media/tuners/tda18218.c
> index 2d31aeb6b088..e4e662c2e6ef 100644
> --- a/drivers/media/tuners/tda18218.c
> +++ b/drivers/media/tuners/tda18218.c
> @@ -24,7 +24,7 @@
>  static int tda18218_wr_regs(struct tda18218_priv *priv, u8 reg, u8 *val, u8 len)
>  {
>  	int ret = 0, len2, remaining;
> -	u8 buf[1 + len];
> +	u8 buf[80];
>  	struct i2c_msg msg[1] = {
>  		{
>  			.addr = priv->cfg->i2c_address,
> @@ -33,6 +33,13 @@ static int tda18218_wr_regs(struct tda18218_priv *priv, u8 reg, u8 *val, u8 len)
>  		}
>  	};
>  
> +	if (1 + len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c wr reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +
>  	for (remaining = len; remaining > 0;
>  			remaining -= (priv->cfg->i2c_wr_max - 1)) {
>  		len2 = remaining;
> @@ -63,7 +70,7 @@ static int tda18218_wr_regs(struct tda18218_priv *priv, u8 reg, u8 *val, u8 len)
>  static int tda18218_rd_regs(struct tda18218_priv *priv, u8 reg, u8 *val, u8 len)
>  {
>  	int ret;
> -	u8 buf[reg+len]; /* we must start read always from reg 0x00 */
> +	u8 buf[80]; /* we must start read always from reg 0x00 */
>  	struct i2c_msg msg[2] = {
>  		{
>  			.addr = priv->cfg->i2c_address,
> @@ -78,6 +85,13 @@ static int tda18218_rd_regs(struct tda18218_priv *priv, u8 reg, u8 *val, u8 len)
>  		}
>  	};
>  
> +	if (reg + len > sizeof(buf)) {
> +		dev_warn(&priv->i2c->dev,
> +			 "%s: i2c wr reg=%04x: len=%d is too big!\n",
> +			 KBUILD_MODNAME, reg, len);
> +		return -EREMOTEIO;
> +	}
> +
>  	ret = i2c_transfer(priv->i2c, msg, 2);
>  	if (ret == 2) {
>  		memcpy(val, &buf[reg], len);
>