Re: [PATCH v2 1/2] platform/x86: dell-smbios: Fix wrong token data in sysfs

[Ilpo Järvinen]

On Tue, 28 May 2024, Armin Wolf wrote:

> When reading token data from sysfs on my Inspiron 3505, the token
> locations and values are wrong. This happens because match_attribute()
> blindly assumes that all entries in da_tokens have an associated
> entry in token_attrs.
> 
> This however is not true as soon as da_tokens[] contains zeroed
> token entries. Those entries are being skipped when initialising
> token_attrs, breaking the core assumption of match_attribute().
> 
> Fix this by defining an extra struct for each pair of token attributes
> and use container_of() to retrieve token information.
> 
> Tested on a Dell Inspiron 3050.
> 
> Fixes: 33b9ca1e53b4 ("platform/x86: dell-smbios: Add a sysfs interface for SMBIOS tokens")
> Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
> ---
> Changes since v1:
> - remove style changes
> - improve sizeof() usage with pointer targets
> ---
>  drivers/platform/x86/dell/dell-smbios-base.c | 92 ++++++++------------
>  1 file changed, 36 insertions(+), 56 deletions(-)
> 
> diff --git a/drivers/platform/x86/dell/dell-smbios-base.c b/drivers/platform/x86/dell/dell-smbios-base.c
> index e61bfaf8b5c4..86b95206cb1b 100644
> --- a/drivers/platform/x86/dell/dell-smbios-base.c
> +++ b/drivers/platform/x86/dell/dell-smbios-base.c
> @@ -11,6 +11,7 @@
>   */
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> 
> +#include <linux/container_of.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/capability.h>
> @@ -25,11 +26,16 @@ static u32 da_supported_commands;
>  static int da_num_tokens;
>  static struct platform_device *platform_device;
>  static struct calling_interface_token *da_tokens;
> -static struct device_attribute *token_location_attrs;
> -static struct device_attribute *token_value_attrs;
> +static struct token_sysfs_data *token_entries;
>  static struct attribute **token_attrs;
>  static DEFINE_MUTEX(smbios_mutex);
> 
> +struct token_sysfs_data {
> +	struct device_attribute location_attr;
> +	struct device_attribute value_attr;
> +	struct calling_interface_token *token;
> +};
> +
>  struct smbios_device {
>  	struct list_head list;
>  	struct device *device;
> @@ -416,47 +422,26 @@ static void __init find_tokens(const struct dmi_header *dm, void *dummy)
>  	}
>  }
> 
> -static int match_attribute(struct device *dev,
> -			   struct device_attribute *attr)
> -{
> -	int i;
> -
> -	for (i = 0; i < da_num_tokens * 2; i++) {
> -		if (!token_attrs[i])
> -			continue;
> -		if (strcmp(token_attrs[i]->name, attr->attr.name) == 0)
> -			return i/2;
> -	}
> -	dev_dbg(dev, "couldn't match: %s\n", attr->attr.name);
> -	return -EINVAL;
> -}
> -
>  static ssize_t location_show(struct device *dev,
>  			     struct device_attribute *attr, char *buf)
>  {
> -	int i;
> +	struct token_sysfs_data *data = container_of(attr, struct token_sysfs_data, location_attr);
> 
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EPERM;
> 
> -	i = match_attribute(dev, attr);
> -	if (i > 0)
> -		return sysfs_emit(buf, "%08x", da_tokens[i].location);
> -	return 0;
> +	return sysfs_emit(buf, "%08x", data->token->location);
>  }
> 
>  static ssize_t value_show(struct device *dev,
>  			  struct device_attribute *attr, char *buf)
>  {
> -	int i;
> +	struct token_sysfs_data *data = container_of(attr, struct token_sysfs_data, value_attr);
> 
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EPERM;
> 
> -	i = match_attribute(dev, attr);
> -	if (i > 0)
> -		return sysfs_emit(buf, "%08x", da_tokens[i].value);
> -	return 0;
> +	return sysfs_emit(buf, "%08x", data->token->value);
>  }
> 
>  static struct attribute_group smbios_attribute_group = {
> @@ -473,22 +458,15 @@ static int build_tokens_sysfs(struct platform_device *dev)
>  {
>  	char *location_name;
>  	char *value_name;
> -	size_t size;
>  	int ret;
>  	int i, j;
> 
> -	/* (number of tokens  + 1 for null terminated */
> -	size = sizeof(struct device_attribute) * (da_num_tokens + 1);
> -	token_location_attrs = kzalloc(size, GFP_KERNEL);
> -	if (!token_location_attrs)
> +	token_entries = kcalloc(da_num_tokens, sizeof(*token_entries), GFP_KERNEL);
> +	if (!token_entries)
>  		return -ENOMEM;
> -	token_value_attrs = kzalloc(size, GFP_KERNEL);
> -	if (!token_value_attrs)
> -		goto out_allocate_value;
> 
>  	/* need to store both location and value + terminator*/
> -	size = sizeof(struct attribute *) * ((2 * da_num_tokens) + 1);
> -	token_attrs = kzalloc(size, GFP_KERNEL);
> +	token_attrs = kcalloc((2 * da_num_tokens) + 1, sizeof(*token_attrs), GFP_KERNEL);

This isn't actually required for the fix since it's in practice just a
syntatic cleanup but then it is harmful either.

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>

-- 
 i.

>  	if (!token_attrs)
>  		goto out_allocate_attrs;
> 
> @@ -496,27 +474,32 @@ static int build_tokens_sysfs(struct platform_device *dev)
>  		/* skip empty */
>  		if (da_tokens[i].tokenID == 0)
>  			continue;
> +
> +		token_entries[i].token = &da_tokens[i];
> +
>  		/* add location */
>  		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);
> -		token_location_attrs[i].attr.name = location_name;
> -		token_location_attrs[i].attr.mode = 0444;
> -		token_location_attrs[i].show = location_show;
> -		token_attrs[j++] = &token_location_attrs[i].attr;
> +
> +		sysfs_attr_init(&token_entries[i].location_attr.attr);
> +		token_entries[i].location_attr.attr.name = location_name;
> +		token_entries[i].location_attr.attr.mode = 0444;
> +		token_entries[i].location_attr.show = location_show;
> +		token_attrs[j++] = &token_entries[i].location_attr.attr;
> 
>  		/* add value */
>  		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);
> -		token_value_attrs[i].attr.name = value_name;
> -		token_value_attrs[i].attr.mode = 0444;
> -		token_value_attrs[i].show = value_show;
> -		token_attrs[j++] = &token_value_attrs[i].attr;
> +
> +		sysfs_attr_init(&token_entries[i].value_attr.attr);
> +		token_entries[i].value_attr.attr.name = value_name;
> +		token_entries[i].value_attr.attr.mode = 0444;
> +		token_entries[i].value_attr.show = value_show;
> +		token_attrs[j++] = &token_entries[i].value_attr.attr;
>  		continue;
> 
>  loop_fail_create_value:
> @@ -532,14 +515,12 @@ static int build_tokens_sysfs(struct platform_device *dev)
> 
>  out_unwind_strings:
>  	while (i--) {
> -		kfree(token_location_attrs[i].attr.name);
> -		kfree(token_value_attrs[i].attr.name);
> +		kfree(token_entries[i].location_attr.attr.name);
> +		kfree(token_entries[i].value_attr.attr.name);
>  	}
>  	kfree(token_attrs);
>  out_allocate_attrs:
> -	kfree(token_value_attrs);
> -out_allocate_value:
> -	kfree(token_location_attrs);
> +	kfree(token_entries);
> 
>  	return -ENOMEM;
>  }
> @@ -551,12 +532,11 @@ static void free_group(struct platform_device *pdev)
>  	sysfs_remove_group(&pdev->dev.kobj,
>  				&smbios_attribute_group);
>  	for (i = 0; i < da_num_tokens; i++) {
> -		kfree(token_location_attrs[i].attr.name);
> -		kfree(token_value_attrs[i].attr.name);
> +		kfree(token_entries[i].location_attr.attr.name);
> +		kfree(token_entries[i].value_attr.attr.name);
>  	}
>  	kfree(token_attrs);
> -	kfree(token_value_attrs);
> -	kfree(token_location_attrs);
> +	kfree(token_entries);
>  }
> 
>  static int __init dell_smbios_init(void)
> --
> 2.39.2
>