* [PATCH nf] netfilter: ctnetlink: netns exit must wait for callbacks
@ 2019-11-15 11:39 Florian Westphal
2019-11-29 8:02 ` Pablo Neira Ayuso
0 siblings, 1 reply; 2+ messages in thread
From: Florian Westphal @ 2019-11-15 11:39 UTC (permalink / raw)
To: netfilter-devel; +Cc: Florian Westphal
Curtis Taylor and Jon Maxwell reported and debugged a crash on 3.10
based kernel.
Crash occurs in ctnetlink_conntrack_events because net->nfnl socket is
NULL. The nfnl socket was set to NULL by netns destruction running on
another cpu.
The exiting network namespace calls the relevant destructors in the
following order:
1. ctnetlink_net_exit_batch
This nulls out the event callback pointer in struct netns.
2. nfnetlink_net_exit_batch
This nulls net->nfnl socket and frees it.
3. nf_conntrack_cleanup_net_list
This removes all remaining conntrack entries.
This is order is correct. The only explanation for the crash so ar is:
cpu1: conntrack is dying, eviction occurs:
-> nf_ct_delete()
-> nf_conntrack_event_report \
-> nf_conntrack_eventmask_report
-> notify->fcn() (== ctnetlink_conntrack_events).
cpu1: a. fetches rcu protected pointer to obtain ctnetlink event callback.
b. gets interrupted.
cpu2: runs netns exit handlers:
a runs ctnetlink destructor, event cb pointer set to NULL.
b runs nfnetlink destructor, nfnl socket is closed and set to NULL.
cpu1: c. resumes and trips over NULL net->nfnl.
Problem appears to be that ctnetlink_net_exit_batch only prevents future
callers of nf_conntrack_eventmask_report() from obtaining the callback.
It doesn't wait of other cpus that might have already obtained the
callbacks address.
I don't see anything in upstream kernels that would prevent similar
crash: We need to wait for all cpus to have exited the event callback.
Fixes: 9592a5c01e79dbc59eb56fa ("netfilter: ctnetlink: netns support")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
net/netfilter/nf_conntrack_netlink.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index e2d13cd18875..aa8adf930b3c 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3602,6 +3602,9 @@ static void __net_exit ctnetlink_net_exit_batch(struct list_head *net_exit_list)
list_for_each_entry(net, net_exit_list, exit_list)
ctnetlink_net_exit(net);
+
+ /* wait for other cpus until they are done with ctnl_notifiers */
+ synchronize_rcu();
}
static struct pernet_operations ctnetlink_net_ops = {
--
2.23.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH nf] netfilter: ctnetlink: netns exit must wait for callbacks
2019-11-15 11:39 [PATCH nf] netfilter: ctnetlink: netns exit must wait for callbacks Florian Westphal
@ 2019-11-29 8:02 ` Pablo Neira Ayuso
0 siblings, 0 replies; 2+ messages in thread
From: Pablo Neira Ayuso @ 2019-11-29 8:02 UTC (permalink / raw)
To: Florian Westphal; +Cc: netfilter-devel
Applied, thanks.
^ permalink raw reply [flat|nested] 2+ messages in thread
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