netfilter: ctnetlink: fix race between delete and timeout expiration

Kerin Millar reported hardlockups while running `conntrackd -c'
in a busy firewall. That system (with several processors) was
acting as backup in a primary-backup setup.

After several tries, I found a race condition between the deletion
operation of ctnetlink and timeout expiration. This patch fixes
this problem.

Tested-by: Kerin Millar <kerframil@gmail.com>
Reported-by: Kerin Millar <kerframil@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 11 deletions

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 10687692831e..b49da6c925b3 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -943,20 +943,21 @@ ctnetlink_del_conntrack(struct sock *ctnl, struct sk_buff *skb,
                 }
         }
 
-        if (nf_conntrack_event_report(IPCT_DESTROY, ct,
-                                      NETLINK_CB(skb).pid,
-                                      nlmsg_report(nlh)) < 0) {
+        if (del_timer(&ct->timeout)) {
+                if (nf_conntrack_event_report(IPCT_DESTROY, ct,
+                                              NETLINK_CB(skb).pid,
+                                              nlmsg_report(nlh)) < 0) {
+                        nf_ct_delete_from_lists(ct);
+                        /* we failed to report the event, try later */
+                        nf_ct_insert_dying_list(ct);
+                        nf_ct_put(ct);
+                        return 0;
+                }
+                /* death_by_timeout would report the event again */
+                set_bit(IPS_DYING_BIT, &ct->status);
                 nf_ct_delete_from_lists(ct);
-                /* we failed to report the event, try later */
-                nf_ct_insert_dying_list(ct);
                 nf_ct_put(ct);
-                return 0;
         }
-
-        /* death_by_timeout would report the event again */
-        set_bit(IPS_DYING_BIT, &ct->status);
-
-        nf_ct_kill(ct);
         nf_ct_put(ct);
 
         return 0;