[PATCH 5.15 011/102] fbdev: efifb: Cleanup fb_info in .fb_destroy rather than .remove

Greg Kroah-Hartman
2022-05-16T20:04:14Z

From: Javier Martinez Canillas <javierm@redhat.com>

[ Upstream commit d258d00fb9c7c0cdf9d10c1ded84f10339d2d349 ]

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>
Link: https://patchwork.freedesktop.org/patch/msgid/20220505220540.366218-1-javierm@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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);
@@ -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;
}
--
2.35.1