3.16.83-rc1 review patch. If anyone has any objections, please let me know.
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From: Florian Westphal fw@strlen.de
commit 18a110b022a5c02e7dc9f6109d0bd93e58ac6ebb upstream.
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 Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/netfilter/nf_conntrack_netlink.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/net/netfilter/nf_conntrack_netlink.c +++ b/net/netfilter/nf_conntrack_netlink.c @@ -3225,6 +3225,9 @@ static void __net_exit ctnetlink_net_exi
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 = {