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Mon, 13 Jul 2020 20:53:40 +0000 (UTC) Date: Mon, 13 Jul 2020 14:53:40 -0600 From: Alex Williamson To: Gerd Hoffmann Subject: Re: [PATCH] vfio: fix use-after-free in display Message-ID: <20200713145340.4886d664@x1.home> In-Reply-To: <20200713124520.23266-1-kraxel@redhat.com> References: <20200713124520.23266-1-kraxel@redhat.com> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=alex.williamson@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/13 01:36:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 13 Jul 2020 14:45:20 +0200 Gerd Hoffmann wrote: > Calling ramfb_display_update() might replace the DisplaySurface with the > boot display, which in turn will free the currently active > DisplaySurface. > > So clear our DisplaySurface pinter (dpy->region.surface pointer) to (a) ^o > avoid use-after-free and (b) force replacing the boot display with the > real display when switching back. > > Signed-off-by: Gerd Hoffmann > --- > hw/vfio/display.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/hw/vfio/display.c b/hw/vfio/display.c > index a57a22674d62..342054193b3c 100644 > --- a/hw/vfio/display.c > +++ b/hw/vfio/display.c > @@ -405,6 +405,7 @@ static void vfio_display_region_update(void *opaque) > if (!plane.drm_format || !plane.size) { > if (dpy->ramfb) { > ramfb_display_update(dpy->con, dpy->ramfb); > + dpy->region.surface = NULL; > } > return; > } Tricky, but I think I follow that dpy->region.surface is only ever allocated to replace dpy->con->surface, so when ramfb_display_update() then replaces and frees dpy->con->surface with dpy->ramfb->ds, that's where the object point to by dpy->region.surface was freed. Right? If so, looks ok to me. If you're constructing a pull request, I'll give you an: Acked-by: Alex Williamson Reviewed-by: Alex Williamson If you need me to send a pull, let me know. Thanks, Alex