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 <tzimmermann@suse.de>
Fixes: 873eb3b1 ("fbdev: Disable sysfb device registration when removing conflicting FBs")
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Changcheng Deng <deng.changcheng@zte.com.cn>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpu/drm/drm_aperture.c

@@ -329,15 +329,7 @@ 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;
-
-	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
-		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
-			continue;
-		base = pci_resource_start(pdev, bar);
-		size = pci_resource_len(pdev, bar);
-		drm_aperture_detach_drivers(base, size);
-	}
+	int bar, ret;
 
 	/*
 	 * WARNING: Apparently we must kick fbdev drivers before vgacon,
@@ -345,9 +337,21 @@ int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
 	 */
 #if IS_REACHABLE(CONFIG_FB)
 	ret = remove_conflicting_pci_framebuffers(pdev, req_driver->name);
+	if (ret)
+		return ret;
 #endif
-	if (ret == 0)
 	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))
+			continue;
+		base = pci_resource_start(pdev, bar);
+		size = pci_resource_len(pdev, bar);
+		drm_aperture_detach_drivers(base, size);
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);