KVM: Destroy target device if coalesced MMIO unregistration fails

Destroy and free the target coalesced MMIO device if unregistering said
device fails.  As clearly noted in the code, kvm_io_bus_unregister_dev()
does not destroy the target device.

  BUG: memory leak
  unreferenced object 0xffff888112a54880 (size 64):
    comm "syz-executor.2", pid 5258, jiffies 4297861402 (age 14.129s)
    hex dump (first 32 bytes):
      38 c7 67 15 00 c9 ff ff 38 c7 67 15 00 c9 ff ff  8.g.....8.g.....
      e0 c7 e1 83 ff ff ff ff 00 30 67 15 00 c9 ff ff  .........0g.....
    backtrace:
      [<0000000006995a8a>] kmalloc include/linux/slab.h:556 [inline]
      [<0000000006995a8a>] kzalloc include/linux/slab.h:690 [inline]
      [<0000000006995a8a>] kvm_vm_ioctl_register_coalesced_mmio+0x8e/0x3d0 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:150
      [<00000000022550c2>] kvm_vm_ioctl+0x47d/0x1600 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3323
      [<000000008a75102f>] vfs_ioctl fs/ioctl.c:46 [inline]
      [<000000008a75102f>] file_ioctl fs/ioctl.c:509 [inline]
      [<000000008a75102f>] do_vfs_ioctl+0xbab/0x1160 fs/ioctl.c:696
      [<0000000080e3f669>] ksys_ioctl+0x76/0xa0 fs/ioctl.c:713
      [<0000000059ef4888>] __do_sys_ioctl fs/ioctl.c:720 [inline]
      [<0000000059ef4888>] __se_sys_ioctl fs/ioctl.c:718 [inline]
      [<0000000059ef4888>] __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:718
      [<000000006444fa05>] do_syscall_64+0x9f/0x4e0 arch/x86/entry/common.c:290
      [<000000009a4ed50b>] entry_SYSCALL_64_after_hwframe+0x49/0xbe

  BUG: leak checking failed

Fixes: 5d3c4c7 ("KVM: Stop looking for coalesced MMIO zones if the bus is destroyed")
Cc: [email protected]
Reported-by: 柳菁峰 <[email protected]>
Reported-by: Michal Luczaj <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Link: https://lore.kernel.org/all/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

virt/kvm/coalesced_mmio.c

@@ -187,15 +187,17 @@ int kvm_vm_ioctl_unregister_coalesced_mmio(struct kvm *kvm,
 			r = kvm_io_bus_unregister_dev(kvm,
 				zone->pio ? KVM_PIO_BUS : KVM_MMIO_BUS, &dev->dev);
 
+			kvm_iodevice_destructor(&dev->dev);
+
 			/*
 			 * On failure, unregister destroys all devices on the
 			 * bus _except_ the target device, i.e. coalesced_zones
-			 * has been modified.  No need to restart the walk as
-			 * there aren't any zones left.
+			 * has been modified.  Bail after destroying the target
+			 * device, there's no need to restart the walk as there
+			 * aren't any zones left.
 			 */
 			if (r)
 				break;
-			kvm_iodevice_destructor(&dev->dev);
 		}
 	}