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

[Emil Velikov]

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;
 
    list_inithead(&wsi->connectors);
-- 
2.21.0