[PATCH 0/2] Drivers: hv: vmbus: Fix the error paths of channel setup

[Yuqiang Sun]

When setting up a channel fails, vmbus_add_channel_work() and
vmbus_device_register() do not agree on who cleans up:

- vmbus_add_channel_kobj() drops the channel's last reference when it
  fails, and its callers then use the channel and drop it again (patch 1;
  this is what our static analysis reported, for the sub-channel path).
  Paths that fail before it put a kobject that was never initialized.

- When vmbus_device_register() fails, the device's release calls
  hv_process_channel_removal() on a channel that was not rescinded, which
  hits BUG_ON(!channel->rescind); vmbus_add_channel_work() would then
  clean the channel up a second time (patch 2).

Testing: QEMU (x86_64, KVM, kvm=off with the hv-* enlightenments,
vmbus-bridge and hv-balloon) with KASAN, hv_vmbus and hv_balloon as
modules loaded from init after failslab is armed, on mainline
d135ab453a74. failslab is limited to allocations under
vmbus_device_register(), and fails the N-th one when the hv-balloon
offer is processed. Without the series, every run hits the BUG_ON:
24 of 24 with the failure in device_register(), and 30 of 30 with it in
the channels kset, the channel's kobject_add() or its sysfs group.
With both patches, all 54 runs leave the offer unbound with "unable to
add child device object" and report nothing (no BUG, KASAN, WARNING or
refcount_t message). The sub-channel path of patch 1 is not covered:
QEMU's VMBus offers no sub-channels.

The failures need an allocation failure while the guest processes a
channel offer from the host.

Yuqiang Sun (2):
  Drivers: hv: vmbus: Keep the channel when vmbus_add_channel_kobj()
    fails
  Drivers: hv: vmbus: Do not remove the channel when device registration
    fails

 drivers/hv/channel_mgmt.c |  5 +++--
 drivers/hv/hyperv_vmbus.h |  1 +
 drivers/hv/vmbus_drv.c    | 43 +++++++++++++++++++++++++++++----------
 3 files changed, 36 insertions(+), 13 deletions(-)


base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e
-- 
2.53.0