linux-kernel - Re: [PATCH v4 1/1] nvmem: Add support for write-only instances

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Date:   Tue, 17 Mar 2020 14:35:44 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH v4 1/1] nvmem: Add support for write-only instances



On 17/03/2020 01:01, Nicholas Johnson wrote:
> There is at least one real-world use-case for write-only nvmem
> instances. Refer to 03cd45d2e219 ("thunderbolt: Prevent crash if
> non-active NVMem file is read").
> 
> Add support for write-only nvmem instances by adding attrs for 0200.
> 
> Change nvmem_register() to abort if NULL group is returned from
> nvmem_sysfs_get_groups().
> 
> Return NULL from nvmem_sysfs_get_groups() in invalid cases.
> 
> Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
> ---
>   drivers/nvmem/core.c        |  9 ++++--
>   drivers/nvmem/nvmem-sysfs.c | 56 +++++++++++++++++++++++++++++++------
>   2 files changed, 54 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index ef326f243..95ea9a3b2 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -373,6 +373,12 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>   	nvmem->type = config->type;
>   	nvmem->reg_read = config->reg_read;
>   	nvmem->reg_write = config->reg_write;
> +	nvmem->dev.groups = nvmem_sysfs_get_groups(nvmem, config);
> +	if (!nvmem->dev.groups) {
> +		kfree(nvmem);
> +		return ERR_PTR(-EINVAL);

When I meant leaking here, not just memory but other resources like idr 
and gpio.

You should do something like this:

if (!nvmem->dev.groups) {
	ida_simple_remove(&nvmem_ida, nvmem->id);
	gpiod_put(nvmem->wp_gpio);
	kfree(nvmem);
	return ERR_PTR(-EINVAL);
}

> +	}
> +
>   	if (!config->no_of_node)
>   		nvmem->dev.of_node = config->dev->of_node;
>   
> @@ -387,8 +393,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>   	nvmem->read_only = device_property_present(config->dev, "read-only") ||
>   			   config->read_only || !nvmem->reg_write;
>   
> -	nvmem->dev.groups = nvmem_sysfs_get_groups(nvmem, config);
> -
>   	device_initialize(&nvmem->dev);
>   
>   	dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
> @@ -430,7 +434,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>   	device_del(&nvmem->dev);
>   err_put_device:
>   	put_device(&nvmem->dev);
> -
unnecessary cleanup here!

Other than that every thing looks good to me!


--srini

>   	return ERR_PTR(rval);
>   }
>   EXPORT_SYMBOL_GPL(nvmem_register);
> diff --git a/drivers/nvmem/nvmem-sysfs.c b/drivers/nvmem/nvmem-sysfs.c
> index 9e0c429cd..4ceac8680 100644
> --- a/drivers/nvmem/nvmem-sysfs.c
> +++ b/drivers/nvmem/nvmem-sysfs.c
> @@ -196,16 +196,49 @@ static const struct attribute_group *nvmem_ro_root_dev_groups[] = {
>   	NULL,
>   };
>   
> +/* write only permission, root only */
> +static struct bin_attribute bin_attr_wo_root_nvmem = {
> +	.attr	= {
> +		.name	= "nvmem",
> +		.mode	= 0200,
> +	},
> +	.write	= bin_attr_nvmem_write,
> +};
> +
> +static struct bin_attribute *nvmem_bin_wo_root_attributes[] = {
> +	&bin_attr_wo_root_nvmem,
> +	NULL,
> +};
> +
> +static const struct attribute_group nvmem_bin_wo_root_group = {
> +	.bin_attrs	= nvmem_bin_wo_root_attributes,
> +	.attrs		= nvmem_attrs,
> +};
> +
> +static const struct attribute_group *nvmem_wo_root_dev_groups[] = {
> +	&nvmem_bin_wo_root_group,
> +	NULL,
> +};
> +
>   const struct attribute_group **nvmem_sysfs_get_groups(
>   					struct nvmem_device *nvmem,
>   					const struct nvmem_config *config)
>   {
> -	if (config->root_only)
> -		return nvmem->read_only ?
> -			nvmem_ro_root_dev_groups :
> -			nvmem_rw_root_dev_groups;
> +	/* Read-only */
> +	if (nvmem->reg_read && (!nvmem->reg_write || nvmem->read_only))
> +		return config->root_only ?
> +			nvmem_ro_root_dev_groups : nvmem_ro_dev_groups;
> +
> +	/* Read-write */
> +	if (nvmem->reg_read && nvmem->reg_write && !nvmem->read_only)
> +		return config->root_only ?
> +			nvmem_rw_root_dev_groups : nvmem_rw_dev_groups;
> +
> +	/* Write-only, do not honour request for global writable entry */
> +	if (!nvmem->reg_read && nvmem->reg_write && !nvmem->read_only)
> +		return config->root_only ? nvmem_wo_root_dev_groups : NULL;
>   
> -	return nvmem->read_only ? nvmem_ro_dev_groups : nvmem_rw_dev_groups;
> +	return NULL;
>   }
>   
>   /*
> @@ -224,17 +257,24 @@ int nvmem_sysfs_setup_compat(struct nvmem_device *nvmem,
>   	if (!config->base_dev)
>   		return -EINVAL;
>   
> -	if (nvmem->read_only) {
> +	if (nvmem->reg_read && (!nvmem->reg_write || nvmem->read_only)) {
>   		if (config->root_only)
>   			nvmem->eeprom = bin_attr_ro_root_nvmem;
>   		else
>   			nvmem->eeprom = bin_attr_ro_nvmem;
> -	} else {
> +	} else if (!nvmem->reg_read && nvmem->reg_write && !nvmem->read_only) {
> +		if (config->root_only)
> +			nvmem->eeprom = bin_attr_wo_root_nvmem;
> +		else
> +			return -EINVAL;
> +	} else if (nvmem->reg_read && nvmem->reg_write && !nvmem->read_only) {
>   		if (config->root_only)
>   			nvmem->eeprom = bin_attr_rw_root_nvmem;
>   		else
>   			nvmem->eeprom = bin_attr_rw_nvmem;
> -	}
> +	} else
> +		return -EINVAL;
> +
>   	nvmem->eeprom.attr.name = "eeprom";
>   	nvmem->eeprom.size = nvmem->size;
>   #ifdef CONFIG_DEBUG_LOCK_ALLOC
>