On 06.05.2022 00:05, Javier Martinez Canillas wrote:
The driver is calling framebuffer_release() in its .remove callback, but this will cause the struct fb_info to be freed too early. Since it could be that a reference is still hold to it if user-space opened the fbdev.
This would lead to a use-after-free error if the framebuffer device was unregistered but later a user-space process tries to close the fbdev fd.
To prevent this, move the framebuffer_release() call to fb_ops.fb_destroy instead of doing it in the driver's .remove callback.
Strictly speaking, the code flow in the driver is still wrong because all the hardware cleanupd (i.e: iounmap) should be done in .remove while the software cleanup (i.e: releasing the framebuffer) should be done in the .fb_destroy handler. But this at least makes to match the behavior before commit 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal").
Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal") Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Thomas Zimmermann tzimmermann@suse.de Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
(no changes since v1)
drivers/video/fbdev/efifb.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c index ea42ba6445b2..cfa3dc0b4eee 100644 --- a/drivers/video/fbdev/efifb.c +++ b/drivers/video/fbdev/efifb.c @@ -243,6 +243,10 @@ static void efifb_show_boot_graphics(struct fb_info *info) static inline void efifb_show_boot_graphics(struct fb_info *info) {} #endif
+/*
- fb_ops.fb_destroy is called by the last put_fb_info() call at the end
- of unregister_framebuffer() or fb_release(). Do any cleanup here.
- */ static void efifb_destroy(struct fb_info *info) { if (efifb_pci_dev)
@@ -254,6 +258,9 @@ static void efifb_destroy(struct fb_info *info) else memunmap(info->screen_base); }
- framebuffer_release(info);
- if (request_mem_succeeded) release_mem_region(info->apertures->ranges[0].base, info->apertures->ranges[0].size);
You are releasing info, then you are using it.
I suspect it is responsible for multiple failures of Intel CI [1].
[1]: http://gfx-ci.fi.intel.com/tree/drm-tip/CI_DRM_11615/fi-adl-ddr5/boot0.txt
Regards Andrzej
@@ -620,9 +627,9 @@ static int efifb_remove(struct platform_device *pdev) { struct fb_info *info = platform_get_drvdata(pdev);
- /* efifb_destroy takes care of info cleanup */ unregister_framebuffer(info); sysfs_remove_groups(&pdev->dev.kobj, efifb_groups);
framebuffer_release(info);
return 0; }