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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id o9-20020a5d62c9000000b0020c5253d903sm11552799wrv.79.2022.05.09.08.30.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 May 2022 08:30:25 -0700 (PDT) Message-ID: <1f788b8f-0bea-1818-349e-b1bc907bf251@redhat.com> Date: Mon, 9 May 2022 17:30:23 +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: Andrzej Hajda , linux-kernel@vger.kernel.org Cc: linux-fbdev@vger.kernel.org, Daniel Vetter , Helge Deller , dri-devel@lists.freedesktop.org, Thomas Zimmermann , Daniel Vetter References: <20220505215947.364694-1-javierm@redhat.com> <20220505220413.365977-1-javierm@redhat.com> <753d0350-42dc-389b-b10b-4533ddcf32ac@intel.com> From: Javier Martinez Canillas In-Reply-To: <753d0350-42dc-389b-b10b-4533ddcf32ac@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org Hello Andrzej, On 5/9/22 16:56, Andrzej Hajda wrote: > On 06.05.2022 00:04, Javier Martinez Canillas wrote: >> From: Daniel Vetter >> >> Most fbdev drivers have issues with the fb_info lifetime, because call to >> framebuffer_release() from their driver's .remove callback, rather than >> doing from fbops.fb_destroy callback. >> >> Doing that will destroy the fb_info too early, while references to it may >> still exist, leading to a use-after-free error. >> >> To prevent this, check the fb_info reference counter when attempting to >> kfree the data structure in framebuffer_release(). That will leak it but >> at least will prevent the mentioned error. >> >> Signed-off-by: Daniel Vetter >> Signed-off-by: Javier Martinez Canillas >> Reviewed-by: Thomas Zimmermann >> --- >> >> (no changes since v1) >> >> drivers/video/fbdev/core/fbsysfs.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c >> index 8c1ee9ecec3d..c2a60b187467 100644 >> --- a/drivers/video/fbdev/core/fbsysfs.c >> +++ b/drivers/video/fbdev/core/fbsysfs.c >> @@ -80,6 +80,10 @@ void framebuffer_release(struct fb_info *info) >> { >> if (!info) >> return; >> + >> + if (WARN_ON(refcount_read(&info->count))) >> + return; >> + > > 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); } fb_helper->fbdev = NULL; @@ -2112,6 +2111,7 @@ static void drm_fbdev_release(struct drm_fb_helper *fb_helper) static void drm_fbdev_fb_destroy(struct fb_info *info) { drm_fbdev_release(info->par); + framebuffer_release(info); } static int drm_fbdev_fb_mmap(struct fb_info *info, struct vm_area_struct *vma) > > Regarding fb drivers, just for stats: > git grep -p framebuffer_release | grep _remove | wc -l > Suggests there is at least 70 incorrect users of this :) > Yes, Daniel already mentioned that most of them get this wrong but I was mostly interested in {simple,efi,vesa}fb since are used with "nomodeset". But given that I only touched those tree and still managed to introduce a regression, I won't attempt to fix the others. -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat