[v1] hw/display/qxl: unregister vm_change_state handler and BHs on device exit (CVE-2026-63322)

[PATCH] hw/display/qxl: unregister vm_change_state handler and BHs on device exit (CVE-2026-63322)

Posted by jianghaotian.sunday@gmail.com 1 week, 1 day ago

From: Haotian Jiang <jianghaotian.sunday@gmail.com>

qxl_realize_common() registers a vm_change_state handler via
qemu_add_vm_change_state_handler() and creates three bottom halves
(update_irq, update_area_bh, cursor_bh), but none are ever cleaned up.
The return value of qemu_add_vm_change_state_handler() is discarded, so
the handler is never removed from the global list, and there is no
PCIDeviceClass.exit callback to delete the BHs.

When a secondary QXL device (hotpluggable by default) is hot-unplugged
via device_del, the PCIQXLDevice memory is freed but the vm_state
handler and BH entries remain with dangling opaque pointers. On the
next VM state change (stop/cont/migrate) or BH dispatch, the callback
dereferences freed memory, causing a use-after-free.

Fix this by storing the VMChangeStateEntry returned by
qemu_add_vm_change_state_handler() and adding a qxl_exit() callback
that deletes the vm_state handler, all three BHs, and the
guest_surfaces.cmds allocation before the device memory is freed.

Fixes: a19cbfb34642 ("spice: add qxl device")
Fixes: CVE-2026-63322
Reported-by: Haotian Jiang of Tencent Security (Yunding Lab) <jianghaotian.sunday@gmail.com>
Signed-off-by: Haotian Jiang <jianghaotian.sunday@gmail.com>
Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3607
---
 hw/display/qxl.c | 29 ++++++++++++++++++++++++++++-
 hw/display/qxl.h |  1 +
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 74258afa58..23608f988a 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -2203,7 +2203,8 @@ static void qxl_realize_common(PCIQXLDevice *qxl, Error **errp)
         error_report_err(err);
     }
 
-    qemu_add_vm_change_state_handler(qxl_vm_change_state_handler, qxl);
+    qxl->vmstate_handler =
+        qemu_add_vm_change_state_handler(qxl_vm_change_state_handler, qxl);
 
     qxl->update_irq = qemu_bh_new_guarded(qxl_update_irq_bh, qxl,
                                           &DEVICE(qxl)->mem_reentrancy_guard);
@@ -2475,6 +2476,31 @@ static const Property qxl_properties[] = {
         DEFINE_PROP_UINT32("yres", PCIQXLDevice, yres, 0),
 };
 
+static void qxl_exit(PCIDevice *dev)
+{
+    PCIQXLDevice *qxl = PCI_QXL(dev);
+
+    if (qxl->vmstate_handler) {
+        qemu_del_vm_change_state_handler(qxl->vmstate_handler);
+        qxl->vmstate_handler = NULL;
+    }
+    if (qxl->update_irq) {
+        qemu_bh_delete(qxl->update_irq);
+        qxl->update_irq = NULL;
+    }
+    if (qxl->update_area_bh) {
+        qemu_bh_delete(qxl->update_area_bh);
+        qxl->update_area_bh = NULL;
+    }
+    if (qxl->ssd.cursor_bh) {
+        qemu_bh_delete(qxl->ssd.cursor_bh);
+        qxl->ssd.cursor_bh = NULL;
+    }
+
+    g_free(qxl->guest_surfaces.cmds);
+    qxl->guest_surfaces.cmds = NULL;
+}
+
 static void qxl_pci_class_init(ObjectClass *klass, const void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -2482,6 +2508,7 @@ static void qxl_pci_class_init(ObjectClass *klass, const void *data)
 
     k->vendor_id = REDHAT_PCI_VENDOR_ID;
     k->device_id = QXL_DEVICE_ID_STABLE;
+    k->exit = qxl_exit;
     set_bit(DEVICE_CATEGORY_DISPLAY, dc->categories);
     device_class_set_legacy_reset(dc, qxl_reset_handler);
     dc->vmsd = &qxl_vmstate;
diff --git a/hw/display/qxl.h b/hw/display/qxl.h
index ad8a912878..48d664f777 100644
--- a/hw/display/qxl.h
+++ b/hw/display/qxl.h
@@ -83,6 +83,7 @@ struct PCIQXLDevice {
 
     /* thread signaling */
     QEMUBH             *update_irq;
+    VMChangeStateEntry *vmstate_handler;
 
     /* ram pci bar */
     QXLRam             *ram;
-- 
2.34.1

Re: [PATCH] hw/display/qxl: unregister vm_change_state handler and BHs on device exit (CVE-2026-63322)

Posted by Marc-André Lureau 1 week, 1 day ago

Hi

On Fri, Jul 17, 2026 at 8:54 AM <jianghaotian.sunday@gmail.com> wrote:
>
> From: Haotian Jiang <jianghaotian.sunday@gmail.com>
>
> qxl_realize_common() registers a vm_change_state handler via
> qemu_add_vm_change_state_handler() and creates three bottom halves
> (update_irq, update_area_bh, cursor_bh), but none are ever cleaned up.
> The return value of qemu_add_vm_change_state_handler() is discarded, so
> the handler is never removed from the global list, and there is no
> PCIDeviceClass.exit callback to delete the BHs.
>
> When a secondary QXL device (hotpluggable by default) is hot-unplugged
> via device_del, the PCIQXLDevice memory is freed but the vm_state
> handler and BH entries remain with dangling opaque pointers. On the
> next VM state change (stop/cont/migrate) or BH dispatch, the callback
> dereferences freed memory, causing a use-after-free.
>
> Fix this by storing the VMChangeStateEntry returned by
> qemu_add_vm_change_state_handler() and adding a qxl_exit() callback
> that deletes the vm_state handler, all three BHs, and the
> guest_surfaces.cmds allocation before the device memory is freed.
>
> Fixes: a19cbfb34642 ("spice: add qxl device")
> Fixes: CVE-2026-63322
> Reported-by: Haotian Jiang of Tencent Security (Yunding Lab) <jianghaotian.sunday@gmail.com>
> Signed-off-by: Haotian Jiang <jianghaotian.sunday@gmail.com>
> Cc: qemu-stable@nongnu.org
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3607
> ---
>  hw/display/qxl.c | 29 ++++++++++++++++++++++++++++-
>  hw/display/qxl.h |  1 +
>  2 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/hw/display/qxl.c b/hw/display/qxl.c
> index 74258afa58..23608f988a 100644
> --- a/hw/display/qxl.c
> +++ b/hw/display/qxl.c
> @@ -2203,7 +2203,8 @@ static void qxl_realize_common(PCIQXLDevice *qxl, Error **errp)
>          error_report_err(err);
>      }
>
> -    qemu_add_vm_change_state_handler(qxl_vm_change_state_handler, qxl);
> +    qxl->vmstate_handler =
> +        qemu_add_vm_change_state_handler(qxl_vm_change_state_handler, qxl);
>
>      qxl->update_irq = qemu_bh_new_guarded(qxl_update_irq_bh, qxl,
>                                            &DEVICE(qxl)->mem_reentrancy_guard);
> @@ -2475,6 +2476,31 @@ static const Property qxl_properties[] = {
>          DEFINE_PROP_UINT32("yres", PCIQXLDevice, yres, 0),
>  };
>
> +static void qxl_exit(PCIDevice *dev)
> +{
> +    PCIQXLDevice *qxl = PCI_QXL(dev);
> +
> +    if (qxl->vmstate_handler) {
> +        qemu_del_vm_change_state_handler(qxl->vmstate_handler);
> +        qxl->vmstate_handler = NULL;
> +    }
> +    if (qxl->update_irq) {
> +        qemu_bh_delete(qxl->update_irq);
> +        qxl->update_irq = NULL;
> +    }
> +    if (qxl->update_area_bh) {
> +        qemu_bh_delete(qxl->update_area_bh);
> +        qxl->update_area_bh = NULL;
> +    }
> +    if (qxl->ssd.cursor_bh) {
> +        qemu_bh_delete(qxl->ssd.cursor_bh);
> +        qxl->ssd.cursor_bh = NULL;
> +    }


Please use g_clear_pointer(&bh, qemu_bh_delete).

> +
> +    g_free(qxl->guest_surfaces.cmds);
> +    qxl->guest_surfaces.cmds = NULL;

And g_clear_pointer(&..cmds, g_free)

Hard to say without careful examination if other fields should be
unref/free here...

> +}
> +
>  static void qxl_pci_class_init(ObjectClass *klass, const void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(klass);
> @@ -2482,6 +2508,7 @@ static void qxl_pci_class_init(ObjectClass *klass, const void *data)
>
>      k->vendor_id = REDHAT_PCI_VENDOR_ID;
>      k->device_id = QXL_DEVICE_ID_STABLE;
> +    k->exit = qxl_exit;
>      set_bit(DEVICE_CATEGORY_DISPLAY, dc->categories);
>      device_class_set_legacy_reset(dc, qxl_reset_handler);
>      dc->vmsd = &qxl_vmstate;
> diff --git a/hw/display/qxl.h b/hw/display/qxl.h
> index ad8a912878..48d664f777 100644
> --- a/hw/display/qxl.h
> +++ b/hw/display/qxl.h
> @@ -83,6 +83,7 @@ struct PCIQXLDevice {
>
>      /* thread signaling */
>      QEMUBH             *update_irq;
> +    VMChangeStateEntry *vmstate_handler;
>
>      /* ram pci bar */
>      QXLRam             *ram;
> --
> 2.34.1
>
>