[NETFILTER]: ip_conntrack: fix invalid conntrack statistics RCU assumption

CONNTRACK_STAT_INC assumes rcu_read_lock in nf_hook_slow disables
preemption as well, making it legal to use __get_cpu_var without
disabling preemption manually. The assumption is not correct anymore
with preemptable RCU, additionally we need to protect against softirqs
when not holding ip_conntrack_lock.

Add CONNTRACK_STAT_INC_ATOMIC macro, which disables local softirqs,
and use where necessary.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter_ipv4/ip_conntrack.h

@@ -301,6 +301,12 @@ extern unsigned int ip_conntrack_htable_size;
 extern int ip_conntrack_checksum;
  
 #define CONNTRACK_STAT_INC(count) (__get_cpu_var(ip_conntrack_stat).count++)
+#define CONNTRACK_STAT_INC_ATOMIC(count)		\
+do {							\
+	local_bh_disable();				\
+	__get_cpu_var(ip_conntrack_stat).count++;	\
+	local_bh_enable();				\
+} while (0)
 
 #ifdef CONFIG_IP_NF_CONNTRACK_EVENTS
 #include <linux/notifier.h>

net/ipv4/netfilter/ip_conntrack_core.c

@@ -538,7 +538,7 @@ static int early_drop(struct list_head *chain)
 	if (del_timer(&ct->timeout)) {
 		death_by_timeout((unsigned long)ct);
 		dropped = 1;
-		CONNTRACK_STAT_INC(early_drop);
+		CONNTRACK_STAT_INC_ATOMIC(early_drop);
 	}
 	ip_conntrack_put(ct);
 	return dropped;
@@ -804,7 +804,7 @@ unsigned int ip_conntrack_in(unsigned int hooknum,
 
 	/* Previously seen (loopback or untracked)?  Ignore. */
 	if ((*pskb)->nfct) {
-		CONNTRACK_STAT_INC(ignore);
+		CONNTRACK_STAT_INC_ATOMIC(ignore);
 		return NF_ACCEPT;
 	}
 
@@ -840,20 +840,20 @@ unsigned int ip_conntrack_in(unsigned int hooknum,
 	 * core what to do with the packet. */
 	if (proto->error != NULL
 	    && (ret = proto->error(*pskb, &ctinfo, hooknum)) <= 0) {
-		CONNTRACK_STAT_INC(error);
-		CONNTRACK_STAT_INC(invalid);
+		CONNTRACK_STAT_INC_ATOMIC(error);
+		CONNTRACK_STAT_INC_ATOMIC(invalid);
 		return -ret;
 	}
 
 	if (!(ct = resolve_normal_ct(*pskb, proto,&set_reply,hooknum,&ctinfo))) {
 		/* Not valid part of a connection */
-		CONNTRACK_STAT_INC(invalid);
+		CONNTRACK_STAT_INC_ATOMIC(invalid);
 		return NF_ACCEPT;
 	}
 
 	if (IS_ERR(ct)) {
 		/* Too stressed to deal. */
-		CONNTRACK_STAT_INC(drop);
+		CONNTRACK_STAT_INC_ATOMIC(drop);
 		return NF_DROP;
 	}
 
@@ -865,7 +865,7 @@ unsigned int ip_conntrack_in(unsigned int hooknum,
 		 * the netfilter core what to do*/
 		nf_conntrack_put((*pskb)->nfct);
 		(*pskb)->nfct = NULL;
-		CONNTRACK_STAT_INC(invalid);
+		CONNTRACK_STAT_INC_ATOMIC(invalid);
 		return -ret;
 	}