Re: [PATCH] PCI/sysfs: Use kstrtobool() to parse the ROM attribute input

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jun 12, 2026 at 06:24:48PM +0000, Krzysztof Wilczyński wrote:
> pci_write_rom() controls access to the ROM content through the
> corresponding sysfs attribute, and treats the input as a request to
> disable only when it matches the string "0\n" exactly:
> 
>   if ((off ==  0) && (*buf == '0') && (count == 2))
> 
> The count == 2 condition encodes the trailing newline that echo(1)
> appends.  This was found when software in userspace wrote "0" without
> a trailing newline aiming to disable access, which failed to match the
> condition above and enabled access instead.  For example:
> 
>   $ echo 0 > rom     <- "0\n", count 2, access disabled
>   $ echo -n 0 > rom  <- "0", count 1, access enabled
>   $ echo > rom       <- "", count 1, access enabled (likely not be desirable)
> 
> Thus, parse the input with kstrtobool(), which handles common boolean
> inputs such as "0", "1", "n", "y" or "off", "on", with or without a
> trailing newline, so both of the above disable access, and update the
> now stale comment.
> 
> As a side effect, input that does not parse as a boolean is rejected
> with -EINVAL rather than enabling access.  The documented "0" and "1"
> continue to work as before, and rejecting malformed input brings the
> attribute in line with how sysfs attributes typically handle it.
> 
> Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Applied to pci/sysfs for v7.2, thanks!

> ---
>  drivers/pci/pci-sysfs.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index d37860841260..1ddd6be25d95 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -1309,18 +1309,19 @@ void __weak pci_remove_resource_files(struct pci_dev *dev) { return; }
>   * @off: file offset
>   * @count: number of byte in input
>   *
> - * writing anything except 0 enables it
> + * Writing a boolean value enables or disables the ROM display.
>   */
>  static ssize_t pci_write_rom(struct file *filp, struct kobject *kobj,
>  			     const struct bin_attribute *bin_attr, char *buf,
>  			     loff_t off, size_t count)
>  {
>  	struct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));
> +	bool enable;
>  
> -	if ((off ==  0) && (*buf == '0') && (count == 2))
> -		pdev->rom_attr_enabled = 0;
> -	else
> -		pdev->rom_attr_enabled = 1;
> +	if (kstrtobool(buf, &enable))
> +		return -EINVAL;
> +
> +	pdev->rom_attr_enabled = enable;
>  
>  	return count;
>  }
> -- 
> 2.54.0
>