Hello Thomas,
On 5/9/22 20:32, Thomas Zimmermann wrote:
Hi
Am 09.05.22 um 18:33 schrieb Javier Martinez Canillas:
On 5/9/22 17:51, Andrzej Hajda wrote:
[snip]
Regarding drm: What about drm_fb_helper_fini? It calls also framebuffer_release and is called often from _remove paths (checked intel/radeon/nouveau). I guess it should be fixed as well. Do you plan to fix it?
I think you are correct. Maybe we need something like the following?
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index d265a73313c9..b09598f7af28 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -631,7 +631,6 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper) if (info) { if (info->cmap.len) fb_dealloc_cmap(&info->cmap);
framebuffer_release(info);After reviewing that code, drm_fb_helper_fini() appears to be called from .fb_destroy (see drm_fbdev_release). The code is hard to follow though. If there another way of releasing the framebuffer here?
Andrzej mentioned intel/radeon/nouveau as example, I only looked at i915 and the call chain is the following as far as I can tell:
struct pci_driver i915_pci_driver = { ... .remove = i915_pci_remove, ... };
i915_driver_remove intel_modeset_driver_remove_noirq intel_fbdev_fini intel_fbdev_destroy drm_fb_helper_fini framebuffer_release
So my underdestanding is that if a program has the emulated fbdev device opened and the i915 module is removed, then a use-after-free would be triggered on drm_fbdev_fb_destroy() once the program closes the device:
drm_fbdev_fb_destroy drm_fbdev_release(info->par); <-- info was already freed on .remove