friendly ping Rundong Ge <rdong.ge@xxxxxxxxx> 于2019年4月9日周二 下午2:33写道： > > Hi Pablo > > I've tested on mainline v5.0. The dangling pointer access of fake_rtable > still exists. > > My env is like this: client0--box--client1. > The box runs ubuntu with v5.0 kernel, br_netfilter and nfnetlink_queue > are inserted. > > Reproduce steps: > 1.Create a bridge on the box. > 2.echo 1 >/proc/sys/net/bridge/bridge-nf-call-iptables > 3.Add a netfilter hook function to queue the packets to nfqueuenum 0. > The hook point must between <NF_BR_PRE_ROUTING,NF_BR_PRI_BRNF> and > <NF_BR_FORWARD,NF_BR_PRI_BRNF - 1>. > 4.Add a userspace process "nfqueue_rcv" to continuously read and > set_verdict "NF_ACCEPT" to packets from queue 0. > 5.Continuosly ping client1 from client0 > 6.Send "Ctrl + Z" to pause the "nfqueue_rcv" to simulate the queue > congestion. > 7.Using "ifconfig br0 down&&brctl delbr br0" to delete the bridge. > 8.At this time the _skb_refdst of skbs in the nfqueue become dangling > pointer. If we send "fg" to resume the "nfqueue_rcv", the kernel > may try to access the freed memory. > > Debug log: > Here I add debug logs in "netdev_freemem" and "dst_release" to prove > the freed memory access. As the log shows, the "dst_release" accessed > bridge's fake_rtable after the bridge was freed. > > Apr 8 22:25:14 raydon kernel: [62139.005062] netdev_freemem name:br0, > fake_rtable:000000009d76cef0 > Apr 8 22:25:21 raydon kernel: [62145.967133] dst_release > dst:000000009d76cef0 dst->dev->name: řKU¡TH > Apr 8 22:25:21 raydon kernel: [62145.967154] dst_release > dst:000000009d76cef0 dst->dev->name: řKU¡TH > Apr 8 22:25:21 raydon kernel: [62145.967180] dst_release > dst:000000009d76cef0 dst->dev->name: řKU¡TH > Apr 8 22:25:21 raydon kernel: [62145.967197] dst_release > dst:000000009d76cef0 dst->dev->name: řKU¡TH > > > > The reason why the hook point should be after <NF_BR_PRE_ROUTING, > NF_BR_PRI_BRNF> is skbs reference bridge's fake_rtable in > "br_nf_pre_routing_finish" hooked at <NF_BR_PRE_ROUTING,NF_BR_PRI_BRNF>. > > And the reason why the hook point should be before <NF_BR_FORWARD, > NF_BR_PRI_BRNF - 1> is "br_nf_forward_ip" will set the state.out to > bridge dev. After this hook point, the "nfqnl_dev_drop" triggered by > the bridge's NETDEV_DOWN event can flush the queued skbs before > bridge's memory is freed, because the state.out now matches the > bridge's dev. > > So the root cause is "nfqnl_dev_drop" didn't flush the skbs properly > queued between <NF_BR_PRE_ROUTING,NF_BR_PRI_BRNF> and <NF_BR_FORWARD, > NF_BR_PRI_BRNF - 1>. > > As you mentioned, hold the bridge dev for these skbs is not a proper > solution. I will send another patch to let "nfqnl_dev_drop" can flush > these skbs. > > Thanks > Rundong > > > Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> 于2019年4月4日周四 上午1:44写道： > > > > On Tue, Apr 02, 2019 at 12:56:09PM +0000, Rundong Ge wrote: > > > Problem: > > > When bridge-nf-call-iptables is enabled, skb_dst(skb) of packets that > > > in the nfqueue may be a dangling pointer if user delete the bridge. > > > Because packets go through the br_nf_pre_routing_finish will set the dst > > > pointer to the br->fake_rtable. But the br struct will be freed > > > without the reference check for these skbs. > > > > > > User impact: > > > Kernel panic may happen when user delete the bridge if there are > > > continuous traffics go through the nfqueue. > > > Here is a panic in my device which using kernel v3.10. > > > > This kernel is _very old_. > > > > Could you provide the steps to reproduce this issue? > > > > Holding the device doesn't seem the way to go to me, we have a of > > netdevice_notifier that is dropping packets for an interface that is > > gone in nfnetlink_queue. We also drop packets whenever a hook in gone. > > > > So I wonder if this is still a problem in mainline kernels.
