Unverified Commit b3c9a924 authored May 06, 2022 by Javier Martinez Canillas

fbdev: vesafb: Cleanup fb_info in .fb_destroy rather than .remove



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 27599aac ("fbdev: Hot-unplug firmware fb devices on forced removal").

Fixes: 27599aac ("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>
Link: https://patchwork.freedesktop.org/patch/msgid/20220505220631.366371-1-javierm@redhat.com

parent d258d00f

drivers/video/fbdev/vesafb.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -179,6 +179,10 @@ static int vesafb_setcolreg(unsigned regno, unsigned red, unsigned green,
		return err;
		}

		/*
		* 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 vesafb_destroy(struct fb_info *info)
		{
		struct vesafb_par *par = info->par;
		@@ -188,6 +192,8 @@ static void vesafb_destroy(struct fb_info *info)
		if (info->screen_base)
		iounmap(info->screen_base);
		release_mem_region(info->apertures->ranges[0].base, info->apertures->ranges[0].size);

		framebuffer_release(info);
		}

		static struct fb_ops vesafb_ops = {
		@@ -484,10 +490,10 @@ static int vesafb_remove(struct platform_device *pdev)
		{
		struct fb_info *info = platform_get_drvdata(pdev);

		/* vesafb_destroy takes care of info cleanup */
		unregister_framebuffer(info);
		if (((struct vesafb_par *)(info->par))->region)
		release_region(0x3c0, 32);
		framebuffer_release(info);

		return 0;
		}