Re: [PATCH] hwmon: (w83627ehf): fix broken driver init

[Guenter Roeck <guenter.roeck@ericsson.com>]

On Fri, Nov 04, 2011 at 08:54:10PM -0400, Alexander Beregalov wrote:
> Commit 2265cef2 (hwmon: (w83627ehf) Properly report PECI and AMD-SI
> sensor types) results in kernel panic if data->temp_label was not
> initialized.
> The problem was found with chip W83627DHG-P.
> 
> backtrace:
> page_fault()
> w83627ehf_probe() 0x8e2
> 
> w83627ehf_init_device:
> 1837:	for (i = 0; i < 3; i++) {
> 		const char *label = data->temp_label[data->temp_src[i]];
> 
> 		/* Digital source overrides analog type */
> 		if (strncmp(label, "PECI", 4) == 0)
> 			data->temp_type[i] = 6;
> 
> 	movzbl	128(%r14), %edx	# data->temp_src, tmp737
> 	movq	144(%r13), %rax	# data_32->temp_label, data_32->temp_label
> 	movq	$.LC18, %rsi	#,
> 	movl	%r14d, %r15d	#, i
> 	subl	%r13d, %r15d	# D.29277, i
> 0x928	movq	(%rax,%rdx,8), %rcx	#* data_32->temp_label, label
> 	movl	$4, %edx	#,
> 	movq	%rcx, %rdi	# label,
> 	movq	%rcx, -96(%rbp)	#,
> 	call	strncmp	#
> 
> page_fault() is called at 0x928 (0x8e2+0x46).
> 
Oops ...

> Add check if data->temp->label was set before use.
> 
> Cc: Jean Delvare <khali@linux-fr.org>
> Cc: Guenter Roeck <guenter.roeck@ericsson.com>
> Cc: stable@kernel.org
> Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
> ---
>  drivers/hwmon/w83627ehf.c |   17 +++++++++--------
>  1 files changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/hwmon/w83627ehf.c b/drivers/hwmon/w83627ehf.c
> index 483cb26..70f1c73 100644
> --- a/drivers/hwmon/w83627ehf.c
> +++ b/drivers/hwmon/w83627ehf.c
> @@ -1835,14 +1835,15 @@ static inline void __devinit w83627ehf_init_device(struct w83627ehf_data *data,
>  		diode = 0x70;
>  	}
>  	for (i = 0; i < 3; i++) {
> -		const char *label = data->temp_label[data->temp_src[i]];
> -
> -		/* Digital source overrides analog type */
> -		if (strncmp(label, "PECI", 4) == 0)
> -			data->temp_type[i] = 6;
> -		else if (strncmp(label, "AMD", 3) == 0)
> -			data->temp_type[i] = 5;
> -		else if ((tmp & (0x02 << i)))
> +		if (data->temp_label) {
> +			const char *label = data->temp_label[data->temp_src[i]];
> +
> +			/* Digital source overrides analog type */
> +			if (strncmp(label, "PECI", 4) == 0)
> +				data->temp_type[i] = 6;
> +			else if (strncmp(label, "AMD", 3) == 0)
> +				data->temp_type[i] = 5;
> +		} else if ((tmp & (0x02 << i)))

This does not completely fix the problem, since there is now an else case which isn't
covered. Specifically, if there is a label, but the source is neither AMD nor PECI,
temp_type won't be set.

Guenter

>  			data->temp_type[i] = (diode & (0x10 << i)) ? 1 : 3;
>  		else
>  			data->temp_type[i] = 4; /* thermistor */
> -- 
> 1.7.7.2
>