On Thu, Jan 07, 2021 at 06:13:15PM +0000, Tom Parkin wrote: > When setting up a channel bridge, ppp_bridge_channels sets the > pch->bridge field before taking the associated reference on the bridge > file instance. > > This opens up a refcount underflow bug if ppp_bridge_channels called > via. iotcl runs concurrently with ppp_unbridge_channels executing via. > file release. > > The bug is triggered by ppp_bridge_channels taking the error path > through the 'err_unset' label. In this scenario, pch->bridge is set, > but the reference on the bridged channel will not be taken because > the function errors out. If ppp_unbridge_channels observes pch->bridge > before it is unset by the error path, it will erroneously drop the > reference on the bridged channel and cause a refcount underflow. > > To avoid this, ensure that ppp_bridge_channels holds a reference on > each channel in advance of setting the bridge pointers.
Thanks for following up on this! Acked-by: Guillaume Nault <gna...@redhat.com>
