hw/vfio/pci: Fix double free of migration_blocker

When user tries to hotplug a VFIO device, but the operation fails
somewhere in the middle (in my testing it failed because of
RLIMIT_MEMLOCK forbidding more memory allocation), then a double
free occurs. In vfio_realize() the vdev->migration_blocker is
allocated, then something goes wrong which causes control to jump
onto 'error' label where the error is freed. But the pointer is
left pointing to invalid memory. Later, when
vfio_instance_finalize() is called, the memory is freed again.

In my testing the second hunk was sufficient to fix the bug, but
I figured the first hunk doesn't hurt either.

==169952== Invalid read of size 8
==169952==    at 0xA47DCD: error_free (error.c:266)
==169952==    by 0x4E0A18: vfio_instance_finalize (pci.c:3040)
==169952==    by 0x8DF74C: object_deinit (object.c:606)
==169952==    by 0x8DF7BE: object_finalize (object.c:620)
==169952==    by 0x8E0757: object_unref (object.c:1074)
==169952==    by 0x45079C: memory_region_unref (memory.c:1779)
==169952==    by 0x45376B: do_address_space_destroy (memory.c:2793)
==169952==    by 0xA5C600: call_rcu_thread (rcu.c:283)
==169952==    by 0xA427CB: qemu_thread_start (qemu-thread-posix.c:519)
==169952==    by 0x80A8457: start_thread (in /lib64/libpthread-2.29.so)
==169952==    by 0x81C96EE: clone (in /lib64/libc-2.29.so)
==169952==  Address 0x143137e0 is 0 bytes inside a block of size 48 free'd
==169952==    at 0x4A342BB: free (vg_replace_malloc.c:530)
==169952==    by 0xA47E05: error_free (error.c:270)
==169952==    by 0x4E0945: vfio_realize (pci.c:3025)
==169952==    by 0x76A4FF: pci_qdev_realize (pci.c:2099)
==169952==    by 0x689B9A: device_set_realized (qdev.c:876)
==169952==    by 0x8E2C80: property_set_bool (object.c:2080)
==169952==    by 0x8E0EF6: object_property_set (object.c:1272)
==169952==    by 0x8E3FC8: object_property_set_qobject (qom-qobject.c:26)
==169952==    by 0x8E11DB: object_property_set_bool (object.c:1338)
==169952==    by 0x5E7BDD: qdev_device_add (qdev-monitor.c:673)
==169952==    by 0x5E81E5: qmp_device_add (qdev-monitor.c:798)
==169952==    by 0x9E18A8: do_qmp_dispatch (qmp-dispatch.c:132)
==169952==  Block was alloc'd at
==169952==    at 0x4A35476: calloc (vg_replace_malloc.c:752)
==169952==    by 0x51B1158: g_malloc0 (in /usr/lib64/libglib-2.0.so.0.6000.6)
==169952==    by 0xA47357: error_setv (error.c:61)
==169952==    by 0xA475D9: error_setg_internal (error.c:97)
==169952==    by 0x4DF8C2: vfio_realize (pci.c:2737)
==169952==    by 0x76A4FF: pci_qdev_realize (pci.c:2099)
==169952==    by 0x689B9A: device_set_realized (qdev.c:876)
==169952==    by 0x8E2C80: property_set_bool (object.c:2080)
==169952==    by 0x8E0EF6: object_property_set (object.c:1272)
==169952==    by 0x8E3FC8: object_property_set_qobject (qom-qobject.c:26)
==169952==    by 0x8E11DB: object_property_set_bool (object.c:1338)
==169952==    by 0x5E7BDD: qdev_device_add (qdev-monitor.c:673)

Fixes: f045a0104c8c ("vfio: unplug failover primary device before migration")
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index e6569a796850b9e3f66dd61b9ee14f29fd6a5940..9c165995df32570fbe3fcedaacf83897fc161f9d 100644 (file)
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2740,6 +2740,7 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
         if (err) {
             error_propagate(errp, err);
             error_free(vdev->migration_blocker);
+            vdev->migration_blocker = NULL;
             return;
         }
     }
@@ -3023,6 +3024,7 @@ error:
     if (vdev->migration_blocker) {
         migrate_del_blocker(vdev->migration_blocker);
         error_free(vdev->migration_blocker);
+        vdev->migration_blocker = NULL;
     }
 }