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

NF_CT_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 nf_conntrack_lock.

Add NF_CT_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/net/netfilter/nf_conntrack.h

@@ -257,6 +257,12 @@ extern int nf_conntrack_max;
 
 DECLARE_PER_CPU(struct ip_conntrack_stat, nf_conntrack_stat);
 #define NF_CT_STAT_INC(count) (__get_cpu_var(nf_conntrack_stat).count++)
+#define NF_CT_STAT_INC_ATOMIC(count)			\
+do {							\
+	local_bh_disable();				\
+	__get_cpu_var(nf_conntrack_stat).count++;	\
+	local_bh_enable();				\
+} while (0)
 
 /* no helper, no nat */
 #define	NF_CT_F_BASIC	0

net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c

@@ -154,8 +154,8 @@ ipv6_prepare(struct sk_buff **pskb, unsigned int hooknum, unsigned int *dataoff,
 	 */
 	if ((protoff < 0) || (protoff > (*pskb)->len)) {
 		DEBUGP("ip6_conntrack_core: can't find proto in pkt\n");
-		NF_CT_STAT_INC(error);
-		NF_CT_STAT_INC(invalid);
+		NF_CT_STAT_INC_ATOMIC(error);
+		NF_CT_STAT_INC_ATOMIC(invalid);
 		return -NF_ACCEPT;
 	}
 

net/netfilter/nf_conntrack_core.c

@@ -563,7 +563,7 @@ static int early_drop(struct list_head *chain)
 	if (del_timer(&ct->timeout)) {
 		death_by_timeout((unsigned long)ct);
 		dropped = 1;
-		NF_CT_STAT_INC(early_drop);
+		NF_CT_STAT_INC_ATOMIC(early_drop);
 	}
 	nf_ct_put(ct);
 	return dropped;
@@ -821,7 +821,7 @@ nf_conntrack_in(int pf, unsigned int hooknum, struct sk_buff **pskb)
 
 	/* Previously seen (loopback or untracked)?  Ignore. */
 	if ((*pskb)->nfct) {
-		NF_CT_STAT_INC(ignore);
+		NF_CT_STAT_INC_ATOMIC(ignore);
 		return NF_ACCEPT;
 	}
 
@@ -840,8 +840,8 @@ nf_conntrack_in(int pf, unsigned int hooknum, struct sk_buff **pskb)
 	 * core what to do with the packet. */
 	if (l4proto->error != NULL &&
 	    (ret = l4proto->error(*pskb, dataoff, &ctinfo, pf, hooknum)) <= 0) {
-		NF_CT_STAT_INC(error);
-		NF_CT_STAT_INC(invalid);
+		NF_CT_STAT_INC_ATOMIC(error);
+		NF_CT_STAT_INC_ATOMIC(invalid);
 		return -ret;
 	}
 
@@ -849,13 +849,13 @@ nf_conntrack_in(int pf, unsigned int hooknum, struct sk_buff **pskb)
 			       &set_reply, &ctinfo);
 	if (!ct) {
 		/* Not valid part of a connection */
-		NF_CT_STAT_INC(invalid);
+		NF_CT_STAT_INC_ATOMIC(invalid);
 		return NF_ACCEPT;
 	}
 
 	if (IS_ERR(ct)) {
 		/* Too stressed to deal. */
-		NF_CT_STAT_INC(drop);
+		NF_CT_STAT_INC_ATOMIC(drop);
 		return NF_DROP;
 	}
 
@@ -868,7 +868,7 @@ nf_conntrack_in(int pf, unsigned int hooknum, struct sk_buff **pskb)
 		DEBUGP("nf_conntrack_in: Can't track with proto module\n");
 		nf_conntrack_put((*pskb)->nfct);
 		(*pskb)->nfct = NULL;
-		NF_CT_STAT_INC(invalid);
+		NF_CT_STAT_INC_ATOMIC(invalid);
 		return -ret;
 	}