Re: [PATCH v1 1/2] PCI/sysfs: Change read permissions for VPD attributes

[Thomas Weißschuh]

On 2024-11-07 20:56:56+0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@xxxxxxxxxx>
> 
> The Vital Product Data (VPD) attribute is not readable by regular
> user without root permissions. Such restriction is not really needed
> for many devices in the world, as data presented in that VPD is not
> sensitive and access to the HW is safe and tested.
> 
> This change aligns the permissions of the VPD attribute to be accessible
> for read by all users, while write being restricted to root only.
> 
> For the driver, there is a need to opt-in in order to allow this
> functionality.
> 
> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
> ---
>  drivers/pci/vpd.c   | 9 ++++++++-
>  include/linux/pci.h | 7 ++++++-
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/vpd.c b/drivers/pci/vpd.c
> index e4300f5f304f..7c70930abaa0 100644
> --- a/drivers/pci/vpd.c
> +++ b/drivers/pci/vpd.c
> @@ -156,6 +156,7 @@ static ssize_t pci_vpd_read(struct pci_dev *dev, loff_t pos, size_t count,
>  			    void *arg, bool check_size)
>  {
>  	struct pci_vpd *vpd = &dev->vpd;
> +	struct pci_driver *drv;
>  	unsigned int max_len;
>  	int ret = 0;
>  	loff_t end = pos + count;
> @@ -167,6 +168,12 @@ static ssize_t pci_vpd_read(struct pci_dev *dev, loff_t pos, size_t count,
>  	if (pos < 0)
>  		return -EINVAL;
>  
> +	if (!capable(CAP_SYS_ADMIN)) {
> +		drv = to_pci_driver(dev->dev.driver);
> +		if (!drv || !drv->downgrade_vpd_read)
> +			return -EPERM;
> +	}

If you move the check into vpd_attr_is_visible() then the sysfs core
will enforce the permissions and it's obvious for the user if they can
or can't read/write the file.

> +
>  	max_len = check_size ? vpd->len : PCI_VPD_MAX_SIZE;
>  
>  	if (pos >= max_len)
> @@ -317,7 +324,7 @@ static ssize_t vpd_write(struct file *filp, struct kobject *kobj,
>  
>  	return ret;
>  }
> -static BIN_ATTR(vpd, 0600, vpd_read, vpd_write, 0);
> +static BIN_ATTR_RW(vpd, 0);
>  
>  static struct bin_attribute *vpd_attrs[] = {
>  	&bin_attr_vpd,
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 573b4c4c2be6..b8fed74e742e 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -943,6 +943,10 @@ struct module;
>   *		how to manage the DMA themselves and set this flag so that
>   *		the IOMMU layer will allow them to setup and manage their
>   *		own I/O address space.
> + * @downgrade_vpd_read: Device doesn't require root permissions from the users
> + *              to read VPD information. The driver doesn't expose any sensitive
> + *              information through that interface and safe to be accessed by
> + *              unprivileged users.
>   */
>  struct pci_driver {
>  	const char		*name;
> @@ -960,7 +964,8 @@ struct pci_driver {
>  	const struct attribute_group **dev_groups;
>  	struct device_driver	driver;
>  	struct pci_dynids	dynids;
> -	bool driver_managed_dma;
> +	bool driver_managed_dma : 1;
> +	bool downgrade_vpd_read : 1;
>  };
>  
>  #define to_pci_driver(__drv)	\
> -- 
> 2.47.0
>