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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id o41-20020a05600c512900b00394832af31csm1280992wms.0.2022.05.09.13.00.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 May 2022 13:00:42 -0700 (PDT) Message-ID: <2c59cd79-76d4-7829-e1db-88bc31396c8a@redhat.com> Date: Mon, 9 May 2022 22:00:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v3 1/4] fbdev: Prevent possible use-after-free in fb_release() Content-Language: en-US To: Thomas Zimmermann , Andrzej Hajda , linux-kernel@vger.kernel.org Cc: linux-fbdev@vger.kernel.org, Daniel Vetter , Helge Deller , dri-devel@lists.freedesktop.org, Daniel Vetter References: <20220505215947.364694-1-javierm@redhat.com> <20220505220413.365977-1-javierm@redhat.com> <753d0350-42dc-389b-b10b-4533ddcf32ac@intel.com> <1f788b8f-0bea-1818-349e-b1bc907bf251@redhat.com> <3b7fe4fe-fdec-cef2-4e0e-309d9dc4a8af@redhat.com> <51254d3d-af8d-61b3-e8a2-8fd0e583e783@suse.de> From: Javier Martinez Canillas In-Reply-To: <51254d3d-af8d-61b3-e8a2-8fd0e583e783@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org 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 -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat