netfilter: xt_connbytes: Force CT accounting to be enabled

Check at rule install time that CT accounting is enabled. Force it
to be enabled if not while also emitting a warning since this is not
the default state.

This is in preparation for deprecating CONFIG_NF_CT_ACCT upon which
CONFIG_NETFILTER_XT_MATCH_CONNBYTES depended being set.

Added 2 CT accounting support functions:

nf_ct_acct_enabled() - Get CT accounting state.
nf_ct_set_acct() - Enable/disable CT accountuing.

Signed-off-by: Tim Gardner <[e-mail]>
Acked-by: Jan Engelhardt <[e-mail]>
Signed-off-by: Patrick McHardy <[e-mail]>

include/net/netfilter/nf_conntrack_acct.h

···
 extern unsigned int
 seq_print_acct(struct seq_file *s, const struct nf_conn *ct, int dir);
 
+/* Check if connection tracking accounting is enabled */
+static inline bool nf_ct_acct_enabled(struct net *net)
+{
+	return net->ct.sysctl_acct != 0;
+}
+
+/* Enable/disable connection tracking accounting */
+static inline void nf_ct_set_acct(struct net *net, bool enable)
+{
+	net->ct.sysctl_acct = enable;
+}
+
 extern int nf_conntrack_acct_init(struct net *net);
 extern void nf_conntrack_acct_fini(struct net *net);
 

net/netfilter/xt_connbytes.c

···
 	if (ret < 0)
 		pr_info("cannot load conntrack support for proto=%u\n",
 			par->family);
+
+	/*
+	 * This filter cannot function correctly unless connection tracking
+	 * accounting is enabled, so complain in the hope that someone notices.
+	 */
+	if (!nf_ct_acct_enabled(par->net)) {
+		pr_warning("Forcing CT accounting to be enabled\n");
+		nf_ct_set_acct(par->net, true);
+	}
+
 	return ret;
 }