drm/aperture: Run fbdev removal before internal helpers

Always run fbdev removal first to remove simpledrm via sysfb_disable().
This clears the internal state.

The later call to drm_aperture_detach_drivers() then does nothing.
Otherwise, with drm_aperture_detach_drivers() running first, the call to
sysfb_disable() uses inconsistent state.

Example backtrace show below:

  BUG: KASAN: use-after-free in device_del+0x79/0x5f0
  Read of size 8 at addr ffff888108185050 by task systemd-udevd/311
  CPU: 0 PID: 311 Comm: systemd-udevd Tainted: G            E     5.19.0-rc2-1-default+ #1689
  Hardware name: HP ProLiant DL120 G7, BIOS J01 04/21/2011
  Call Trace:
    device_del+0x79/0x5f0
    platform_device_del.part.0+0x19/0xe0
    platform_device_unregister+0x1c/0x30
    sysfb_disable+0x2d/0x70
    remove_conflicting_framebuffers+0x1c/0xf0
    remove_conflicting_pci_framebuffers+0x130/0x1a0
    drm_aperture_remove_conflicting_pci_framebuffers+0x86/0xb0
    mgag200_pci_probe+0x2d/0x140 [mgag200]

Signed-off-by: Thomas Zimmermann <[email protected]>
Fixes: 873eb3b ("fbdev: Disable sysfb device registration when removing conflicting FBs")
Cc: Javier Martinez Canillas <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Zhen Lei <[email protected]>
Cc: Changcheng Deng <[email protected]>
Reviewed-by: Zack Rusin <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

drivers/gpu/drm/drm_aperture.c

@@ -329,7 +329,20 @@ int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
 						     const struct drm_driver *req_driver)
 {
 	resource_size_t base, size;
-	int bar, ret = 0;
+	int bar, ret;
+
+	/*
+	 * WARNING: Apparently we must kick fbdev drivers before vgacon,
+	 * otherwise the vga fbdev driver falls over.
+	 */
+#if IS_REACHABLE(CONFIG_FB)
+	ret = remove_conflicting_pci_framebuffers(pdev, req_driver->name);
+	if (ret)
+		return ret;
+#endif
+	ret = vga_remove_vgacon(pdev);
+	if (ret)
+		return ret;
 
 	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
 		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
@@ -339,15 +352,6 @@ int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
 		drm_aperture_detach_drivers(base, size);
 	}
 
-	/*
-	 * WARNING: Apparently we must kick fbdev drivers before vgacon,
-	 * otherwise the vga fbdev driver falls over.
-	 */
-#if IS_REACHABLE(CONFIG_FB)
-	ret = remove_conflicting_pci_framebuffers(pdev, req_driver->name);
-#endif
-	if (ret == 0)
-		ret = vga_remove_vgacon(pdev);
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);