[Mesa-dev] [PATCH v2] vulkan/wsi: check if the display_fd given is master

[Emil Velikov]

On Fri, 19 Apr 2019 at 16:01, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>
> From: Emil Velikov <emil.velikov at collabora.com>
>
> As effectively required by the extension, we need to ensure we're master
>
> Currently drivers employ vendor specific solutions, which check if the
> device behind the fd is capable*, yet none of them do the master check.
>
> *In the radv case, if acceleration is available.
>
> Instead of duplicating the check in each driver, keep it where it's
> needed and used.
>
> Note this copies libdrm's drmIsMaster() to avoid depending on bleeding
> edge version of the library.
>
> v2: set the fd to -1 if not master (Bas)
>
> Cc: Keith Packard <keithp at keithp.com>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
> Cc: Andres Rodriguez <andresx7 at gmail.com>
> Reported-by: Andres Rodriguez <andresx7 at gmail.com>
> Fixes: da997ebec92 ("vulkan: Add KHR_display extension using DRM [v10]")
> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> ---
>  src/vulkan/wsi/wsi_common_display.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/src/vulkan/wsi/wsi_common_display.c b/src/vulkan/wsi/wsi_common_display.c
> index 74ed36ed646..2be20e85046 100644
> --- a/src/vulkan/wsi/wsi_common_display.c
> +++ b/src/vulkan/wsi/wsi_common_display.c
> @@ -1812,6 +1812,30 @@ fail_attr_init:
>     return ret;
>  }
>
> +
> +/*
> + * Local version fo the libdrm helper. Added to avoid depending on bleeding
> + * edge version of the library.
> + */
> +static int
> +local_drmIsMaster(int fd)
> +{
> +   /* Detect master by attempting something that requires master.
> +    *
> +    * Authenticating magic tokens requires master and 0 is an
> +    * internal kernel detail which we could use. Attempting this on
> +    * a master fd would fail therefore fail with EINVAL because 0
> +    * is invalid.
> +    *
> +    * A non-master fd will fail with EACCES, as the kernel checks
> +    * for master before attempting to do anything else.
> +    *
> +    * Since we don't want to leak implementation details, use
> +    * EACCES.
> +    */
> +   return drmAuthMagic(fd, 0) != -EACCES;
> +}
> +
>  VkResult
>  wsi_display_init_wsi(struct wsi_device *wsi_device,
>                       const VkAllocationCallbacks *alloc,
> @@ -1827,6 +1851,9 @@ wsi_display_init_wsi(struct wsi_device *wsi_device,
>     }
>
>     wsi->fd = display_fd;
> +   if (wsi->fd != -1 && !local_drmIsMaster(wsi->fd))
> +      wsi->fd = -1;
> +
>     wsi->alloc = alloc;
>
Humble ping?

-Emil