linux-kernel - Re: [PATCH] dell-smbios: fix string overflow

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Date:   Wed, 8 Nov 2017 10:22:52 -0800
From:   sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Pali Rohár <pali.rohar@...il.com>,
        Mario Limonciello <mario.limonciello@...l.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>
Cc:     Edward O'Callaghan <quasisec@...gle.com>,
        Hans de Goede <hdegoede@...hat.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dell-smbios: fix string overflow

Hi,

I recommend using "platform/x86: dell-smbios:" in commit header.

On 11/08/2017 04:08 AM, Arnd Bergmann wrote:
> The new sysfs code overwrites two fixed-length character arrays
> that are each one byte shorter than they need to be, to hold
> the trailing \0:
>
> drivers/platform/x86/dell-smbios.c: In function 'build_tokens_sysfs':
> drivers/platform/x86/dell-smbios.c:494:42: error: 'sprintf' writing a terminating nul past the end of the destination [-Werror=format-overflow=]
>     sprintf(buffer_location, "%04x_location",
> drivers/platform/x86/dell-smbios.c:494:3: note: 'sprintf' output 14 bytes into a destination of size 13
> drivers/platform/x86/dell-smbios.c:506:36: error: 'sprintf' writing a terminating nul past the end of the destination [-Werror=format-overflow=]
>     sprintf(buffer_value, "%04x_value",
> drivers/platform/x86/dell-smbios.c:506:3: note: 'sprintf' output 11 bytes into a destination of size 10
Don't need to include the error log in commit message. Just explaining 
the issue is good enough.
>
> This changes it to just use kasprintf(), which always gets it right.
>
> Fixes: 33b9ca1e53b4 ("platform/x86: dell-smbios: Add a sysfs interface for SMBIOS tokens")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/platform/x86/dell-smbios.c | 12 ++++--------
>   1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/platform/x86/dell-smbios.c b/drivers/platform/x86/dell-smbios.c
> index d99edd803c19..6a60db515bda 100644
> --- a/drivers/platform/x86/dell-smbios.c
> +++ b/drivers/platform/x86/dell-smbios.c
> @@ -463,8 +463,6 @@ static struct platform_driver platform_driver = {
>   
>   static int build_tokens_sysfs(struct platform_device *dev)
>   {
> -	char buffer_location[13];
> -	char buffer_value[10];
>   	char *location_name;
>   	char *value_name;
>   	size_t size;
> @@ -491,9 +489,8 @@ static int build_tokens_sysfs(struct platform_device *dev)
>   		if (da_tokens[i].tokenID == 0)
>   			continue;
>   		/* add location */
> -		sprintf(buffer_location, "%04x_location",
> -			da_tokens[i].tokenID);
> -		location_name = kstrdup(buffer_location, GFP_KERNEL);
> +		location_name = kasprintf(GFP_KERNEL, "%04x_location",
> +					  da_tokens[i].tokenID);
>   		if (location_name == NULL)
>   			goto out_unwind_strings;
>   		sysfs_attr_init(&token_location_attrs[i].attr);
> @@ -503,9 +500,8 @@ static int build_tokens_sysfs(struct platform_device *dev)
>   		token_attrs[j++] = &token_location_attrs[i].attr;
>   
>   		/* add value */
> -		sprintf(buffer_value, "%04x_value",
> -			da_tokens[i].tokenID);
> -		value_name = kstrdup(buffer_value, GFP_KERNEL);
> +		value_name = kasprintf(GFP_KERNEL, "%04x_value",
> +				       da_tokens[i].tokenID);
>   		if (value_name == NULL)
>   			goto loop_fail_create_value;
>   		sysfs_attr_init(&token_value_attrs[i].attr);

-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer