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 <[email protected]>
> Signed-off-by: Javier Martinez Canillas <[email protected]>
> Reviewed-by: Thomas Zimmermann <[email protected]>
> Reviewed-by: Daniel Vetter <[email protected]>
> ---
>
> (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;
> }