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[83.57.170.138]) by smtp.gmail.com with ESMTPSA id t20sm9848929ejd.124.2020.07.13.07.09.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Jul 2020 07:09:16 -0700 (PDT) Subject: Re: [PATCH] vfio: fix use-after-free in display To: Gerd Hoffmann References: <20200713124520.23266-1-kraxel@redhat.com> <20200713140028.yoxn77csag7cbbfh@sirius.home.kraxel.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Autocrypt: addr=philmd@redhat.com; keydata= mQINBDXML8YBEADXCtUkDBKQvNsQA7sDpw6YLE/1tKHwm24A1au9Hfy/OFmkpzo+MD+dYc+7 bvnqWAeGweq2SDq8zbzFZ1gJBd6+e5v1a/UrTxvwBk51yEkadrpRbi+r2bDpTJwXc/uEtYAB GvsTZMtiQVA4kRID1KCdgLa3zztPLCj5H1VZhqZsiGvXa/nMIlhvacRXdbgllPPJ72cLUkXf z1Zu4AkEKpccZaJspmLWGSzGu6UTZ7UfVeR2Hcc2KI9oZB1qthmZ1+PZyGZ/Dy+z+zklC0xl XIpQPmnfy9+/1hj1LzJ+pe3HzEodtlVA+rdttSvA6nmHKIt8Ul6b/h1DFTmUT1lN1WbAGxmg CH1O26cz5nTrzdjoqC/b8PpZiT0kO5MKKgiu5S4PRIxW2+RA4H9nq7nztNZ1Y39bDpzwE5Sp bDHzd5owmLxMLZAINtCtQuRbSOcMjZlg4zohA9TQP9krGIk+qTR+H4CV22sWldSkVtsoTaA2 qNeSJhfHQY0TyQvFbqRsSNIe2gTDzzEQ8itsmdHHE/yzhcCVvlUzXhAT6pIN0OT+cdsTTfif MIcDboys92auTuJ7U+4jWF1+WUaJ8gDL69ThAsu7mGDBbm80P3vvUZ4fQM14NkxOnuGRrJxO qjWNJ2ZUxgyHAh5TCxMLKWZoL5hpnvx3dF3Ti9HW2dsUUWICSQARAQABtDJQaGlsaXBwZSBN YXRoaWV1LURhdWTDqSAoUGhpbCkgPHBoaWxtZEByZWRoYXQuY29tPokCVQQTAQgAPwIbDwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AWIQSJweePYB7obIZ0lcuio/1u3q3A3gUCXsfWwAUJ KtymWgAKCRCio/1u3q3A3ircD/9Vjh3aFNJ3uF3hddeoFg1H038wZr/xi8/rX27M1Vj2j9VH 0B8Olp4KUQw/hyO6kUxqkoojmzRpmzvlpZ0cUiZJo2bQIWnvScyHxFCv33kHe+YEIqoJlaQc JfKYlbCoubz+02E2A6bFD9+BvCY0LBbEj5POwyKGiDMjHKCGuzSuDRbCn0Mz4kCa7nFMF5Jv piC+JemRdiBd6102ThqgIsyGEBXuf1sy0QIVyXgaqr9O2b/0VoXpQId7yY7OJuYYxs7kQoXI 6WzSMpmuXGkmfxOgbc/L6YbzB0JOriX0iRClxu4dEUg8Bs2pNnr6huY2Ft+qb41RzCJvvMyu gS32LfN0bTZ6Qm2A8ayMtUQgnwZDSO23OKgQWZVglGliY3ezHZ6lVwC24Vjkmq/2yBSLakZE 6DZUjZzCW1nvtRK05ebyK6tofRsx8xB8pL/kcBb9nCuh70aLR+5cmE41X4O+MVJbwfP5s/RW 9BFSL3qgXuXso/3XuWTQjJJGgKhB6xXjMmb1J4q/h5IuVV4juv1Fem9sfmyrh+Wi5V1IzKI7 RPJ3KVb937eBgSENk53P0gUorwzUcO+ASEo3Z1cBKkJSPigDbeEjVfXQMzNt0oDRzpQqH2vp apo2jHnidWt8BsckuWZpxcZ9+/9obQ55DyVQHGiTN39hkETy3Emdnz1JVHTU0Q== Message-ID: <7e76540f-6d3e-de4b-c26b-2806162f72cb@redhat.com> Date: Mon, 13 Jul 2020 16:09:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200713140028.yoxn77csag7cbbfh@sirius.home.kraxel.org> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=philmd@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/13 02:19:41 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: Alex Williamson , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/13/20 4:00 PM, Gerd Hoffmann wrote: > On Mon, Jul 13, 2020 at 02:51:05PM +0200, Philippe Mathieu-Daudé wrote: >> On 7/13/20 2:45 PM, 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) >>> 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; >>> } >>> >> >> More generic fix: >> >> -- >8 -- >> --- a/ui/console.c >> +++ b/ui/console.c >> @@ -1580,10 +1580,10 @@ void dpy_gfx_replace_surface(QemuConsole *con, >> DisplaySurface *surface) >> { >> DisplayState *s = con->ds; >> - DisplaySurface *old_surface = con->surface; >> + QemuConsole *old_con = con; >> DisplayChangeListener *dcl; >> >> - assert(old_surface != surface || surface == NULL); >> + assert(con->surface != surface || surface == NULL); >> >> con->surface = surface; >> QLIST_FOREACH(dcl, &s->listeners, next) { >> @@ -1594,7 +1594,8 @@ void dpy_gfx_replace_surface(QemuConsole *con, >> dcl->ops->dpy_gfx_switch(dcl, surface); >> } >> } >> - qemu_free_displaysurface(old_surface); >> + qemu_free_displaysurface(old_con->surface); >> + old_con->surface = NULL; > > No. > > That doesn't clear VFIODisplay->region.surface, but it sets > QemuConsole->surface to NULL no matter what got passed to > dpy_gfx_replace_surface(). > > Guesswork based just on the patch chunk doesn't always work, > sometimes you have to consult the source code to see what the > patch actually does ;) I'm certainly not a source of trust producing perfect code :) I appreciate being reviewed on snippets, so I can learn from my mistakes and improve. I looked at the code (ui/console.c was not in the previous context) but I missed to look at the other call sites for dpy_gfx_replace_surface() and how it is used. Thanks, Phil. > > take care, > Gerd >