[QEMU HCI-8.0 PATCH 6/7] hw/display/qxl: unregister vm_change_state handler and BHs #VSTOR-144000

["Denis V. Lunev" <den@openvz.org>]

From: Haotian Jiang <sundayjiang@tencent.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
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3607
Signed-off-by: Haotian Jiang <jianghaotian.sunday@gmail.com>
Cc: qemu-stable@nongnu.org
[ Marc-André - tweak commit message, add TODO ]
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20260720024855.3757499-1-jianghaotian.sunday@gmail.com>
(cherry picked from commit 4727cc883b7e81d2c30b9801af54482d65b84292)
---
 hw/display/qxl.c | 16 +++++++++++++++-
 hw/display/qxl.h |  1 +
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index a6eea18730e..994bfcaa522 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -2225,7 +2225,8 @@ static void qxl_realize_common(PCIQXLDevice *qxl, Error **errp)
     }
 #endif
 
-    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);
@@ -2504,6 +2505,18 @@ static const Property qxl_properties[] = {
                             subsystem_vendor_id, PCI_VENDOR_ID_REDHAT_QUMRANET),
 };
 
+static void qxl_exit(PCIDevice *dev)
+{
+    PCIQXLDevice *qxl = PCI_QXL(dev);
+
+    /* TODO: complete cleanup, error paths etc */
+    g_clear_pointer(&qxl->vmstate_handler, qemu_del_vm_change_state_handler);
+    g_clear_pointer(&qxl->update_irq, qemu_bh_delete);
+    g_clear_pointer(&qxl->update_area_bh, qemu_bh_delete);
+    g_clear_pointer(&qxl->ssd.cursor_bh, qemu_bh_delete);
+    g_clear_pointer(&qxl->guest_surfaces.cmds, g_free);
+}
+
 static void qxl_pci_class_init(ObjectClass *klass, const void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -2511,6 +2524,7 @@ 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 4afdbdd1ed8..a25d9865453 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;
-- 
2.53.0