Re: [PATCH 6/7] firmware_class: add "fd" input file

[Ming Lei]

On Tue, Jul 15, 2014 at 5:38 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> As an alternative to loading bytes from the "data" blob when reading
> firmware, let kernel read from an fd, so that the LSM can reason about
> the origin of firmware contents during userspace on-demand loading.

>From user space view, maybe it is better to keep previous usage and just
check if loading is from 'data' blob or fd in 'echo 0 > loading' of
firmware_loading_store(), then the 'fd' usage becomes very similar with
before.

>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  Documentation/firmware_class/README |   10 +++++
>  drivers/base/firmware_class.c       |   77 ++++++++++++++++++++++++++++++++++-
>  2 files changed, 86 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/firmware_class/README b/Documentation/firmware_class/README
> index 71f86859d7d8..d899bdacba1e 100644
> --- a/Documentation/firmware_class/README
> +++ b/Documentation/firmware_class/README
> @@ -59,6 +59,16 @@
>   8), kernel(driver): Driver code calls release_firmware(fw_entry) releasing
>                  the firmware image and any related resource.
>
> + Alternative loading (via file descriptor):
> + ==========================================
> + Instead of "loading", and "data" above, firmware can be loaded through
> + an open file descriptor as well, via the "fd" file:
> +
> + Replacing steps 2 thorugh 6 above with the following userspace actions,
> + performs the same loading:
> +       - open firmware image file (e.g. as fd 3).
> +       - write fd (e.g. "3") to /sys/class/firmware/xxx/fd.

Then as above, here should be just to replace step 4, 5 as
          - open image in user space
          - echo fd > /sys/class/firmware/xxx/fd

> +
>   High level behavior (driver code):
>   ==================================
>
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index b38cbcd6ebb1..eac996447d28 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -839,6 +839,70 @@ static struct bin_attribute firmware_attr_data = {
>         .write = firmware_data_write,
>  };
>
> +/**
> + * fd_store - set value in the 'fd' control file
> + * @dev: device pointer
> + * @attr: device attribute pointer
> + * @buf: buffer to scan for loading fd value
> + * @count: number of bytes in @buf
> + *
> + * Parses an fd number from buf, and then loads firmware bytes from
> + * the current process's matching open fd.
> + *
> + **/
> +static ssize_t fd_store(struct device *dev,
> +                                struct device_attribute *attr,
> +                                const char *buf, size_t count)
> +{
> +       struct firmware_priv *fw_priv = to_firmware_priv(dev);
> +       struct firmware_buf *fw_buf = fw_priv->buf;
> +       ssize_t retval;
> +       int fd;
> +       struct fd f;
> +
> +       if (!capable(CAP_SYS_RAWIO))
> +               return -EPERM;
> +
> +       retval = kstrtoint(buf, 10, &fd);
> +       if (retval)
> +               return retval;
> +
> +       f = fdget(fd);
> +       if (!f.file)
> +               return -EBADF;
> +
> +       mutex_lock(&fw_lock);
> +       /* If we raced another loader, we must fail. */
> +       if (test_bit(FW_STATUS_DONE, &fw_buf->status)) {
> +               retval = -EINVAL;
> +               goto unlock;
> +       }
> +
> +       fw_load_start(fw_buf);
> +       /* fw_read_file_contents uses vmalloc, not pages. */
> +       fw_buf->is_paged_buf = false;
> +       retval = fw_read_file_contents(f.file, fw_buf);
> +       if (retval) {
> +               /* If we called fw_load_start, we must abort on fail. */
> +               fw_load_abort(fw_priv);
> +               goto unlock;
> +       }
> +
> +       /* Success. */
> +       set_bit(FW_STATUS_DONE, &fw_buf->status);
> +       list_del_init(&fw_buf->pending_list);
> +       complete_all(&fw_buf->completion);
> +
> +unlock:
> +       mutex_unlock(&fw_lock);
> +       fdput(f);
> +
> +       if (retval)
> +               return retval;
> +       return count;
> +}
> +static DEVICE_ATTR_WO(fd);
> +
>  static void firmware_class_timeout_work(struct work_struct *work)
>  {
>         struct firmware_priv *fw_priv = container_of(work,
> @@ -912,10 +976,19 @@ static int _request_firmware_load(struct firmware_priv *fw_priv,
>                 mutex_lock(&fw_lock);
>                 list_del_init(&buf->pending_list);
>                 mutex_unlock(&fw_lock);
> -               dev_err(f_dev, "%s: device_create_file failed\n", __func__);
> +               dev_err(f_dev, "%s: dev_attr_loading failed\n", __func__);
>                 goto err_del_bin_attr;
>         }
>
> +       retval = device_create_file(f_dev, &dev_attr_fd);
> +       if (retval) {
> +               mutex_lock(&fw_lock);
> +               list_del_init(&buf->pending_list);
> +               mutex_unlock(&fw_lock);
> +               dev_err(f_dev, "%s: &dev_attr_fd failed\n", __func__);
> +               goto err_del_loading;
> +       }
> +
>         if (opt_flags & FW_OPT_UEVENT) {
>                 buf->need_uevent = true;
>                 dev_set_uevent_suppress(f_dev, false);
> @@ -933,6 +1006,8 @@ static int _request_firmware_load(struct firmware_priv *fw_priv,
>         if (!buf->data)
>                 retval = -ENOMEM;
>
> +       device_remove_file(f_dev, &dev_attr_fd);
> +err_del_loading:
>         device_remove_file(f_dev, &dev_attr_loading);
>  err_del_bin_attr:
>         device_remove_bin_file(f_dev, &firmware_attr_data);
> --
> 1.7.9.5
>
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