Re: [PATCH 2/2] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered
From: Daniel Vetter <hidden>
Date: 2022-05-04 09:48:12
Also in:
dri-devel, lkml
On Mon, May 02, 2022 at 03:09:44PM +0200, Javier Martinez Canillas wrote:
A reference to the framebuffer device struct fb_info is stored in the file private data, but this reference could no longer be valid and must not be accessed directly. Instead, the file_fb_info() accessor function must be used since it does sanity checking to make sure that the fb_info is valid. This can happen for example if the fbdev driver was one that is using a framebuffer provided by the system firmware. In that case, the fbdev core could unregister the framebuffer device if a real video driver is probed. Reported-by: Maxime Ripard <redacted> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Doesn't this mean we just leak the references? Also anything the driver might refcount in fb_open would be leaked too. I'm not sure what exactly you're trying to fix here, but this looks a bit wrong. Maybe stepping back what fbdev would need, but doesn't have (see the commit reference I dropped on the previous version) is drm_dev_enter/exit around hw access. the file_fb_info check essentially provides that, but with races and everything. But drm_dev_enter/exit should not disable sw side code, especially not refcount cleanup like fb_release does here. -Daniel
quoted hunk ↗ jump to hunk
--- drivers/video/fbdev/core/fbmem.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 20d8929df79f..d68097105f93 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c@@ -1439,7 +1439,10 @@ fb_release(struct inode *inode, struct file *file) __acquires(&info->lock) __releases(&info->lock) { - struct fb_info * const info = file->private_data; + struct fb_info * const info = file_fb_info(file); + + if (!info) + return -ENODEV; lock_fb_info(info); if (info->fbops->fb_release)-- 2.35.1
-- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch