| Message ID | 20220505220540.366218-1-javierm@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | fbdev: Fix use-after-free caused by wrong fb_info cleanup in drivers | expand |
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; > }
Hello Andrzej, On 5/6/22 15:07, Andrzej Hajda wrote: > On 06.05.2022 00:05, Javier Martinez Canillas wrote: [snip] >> + >> + 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]. > Yes, it is :( sorry about the mess. Ville already reported this to me. I'll post a patch in a minute. I wonder how this didn't happen before since .remove() happens before .fb_destroy() AFAIU...
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; }
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(-)