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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id k8-20020adfd848000000b0020c5253d8dbsm11555562wrl.39.2022.05.09.13.03.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 May 2022 13:03:47 -0700 (PDT) Message-ID: <2bf27b09-0896-1849-254f-d5b19abdc892@redhat.com> Date: Mon, 9 May 2022 22:03:46 +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> From: Javier Martinez Canillas In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/9/22 20:12, Thomas Zimmermann wrote: [snip] >> I actually thought about the same but then remembered what Daniel said in [0] >> (AFAIU at least) that these should be done in .remove() so the current code >> looks like matches that and only framebuffer_release() should be moved. >> >> For vesafb a previous patch proposed to also move a release_region() call to >> .fb_destroy() and Daniel also said that it was iffy and shouldn't be done [1]. >> >> But I'm also not fb expert so happy to move fb_dealloc_cmap() as well if that >> is the correct thing to do. > > The cmap data structure is software state that can be accessed via icotl > as long as the devfile is open. Drivers update the hardware from it. See > [1]. Moving that cleanup into fb_destroy seems appropriate to me. > I see, that makes sense. Then something like the following instead? diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index d265a73313c9..ce0d89c49e42 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -627,12 +627,6 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper) cancel_work_sync(&fb_helper->resume_work); cancel_work_sync(&fb_helper->damage_work); - info = fb_helper->fbdev; - if (info) { - if (info->cmap.len) - fb_dealloc_cmap(&info->cmap); - framebuffer_release(info); - } fb_helper->fbdev = NULL; mutex_lock(&kernel_fb_helper_lock); @@ -2111,7 +2105,11 @@ static void drm_fbdev_release(struct drm_fb_helper *fb_helper) */ static void drm_fbdev_fb_destroy(struct fb_info *info) { + if (info->cmap.len) + fb_dealloc_cmap(&info->cmap); + drm_fbdev_release(info->par); + framebuffer_release(info); } static int drm_fbdev_fb_mmap(struct fb_info *info, struct vm_area_struct *vma) -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat