netfilter: restore rule tracing via nfnetlink_log

Since fab4085f ("netfilter: log: nf_log_packet() as real unified
interface"), the loginfo structure that is passed to nf_log_packet() is
used to explicitly indicate the logger type you want to use.

This is a problem for people tracing rules through nfnetlink_log since
packets are always routed to the NF_LOG_TYPE logger after the
aforementioned patch.

We can fix this by removing the trace loginfo structures, but that still
changes the log level from 4 to 5 for tracing messages and there may be
someone relying on this outthere. So let's just introduce a new
nf_log_trace() function that restores the former behaviour.
Reported-by: Markus Kötter <koetter@rrzn.uni-hannover.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_log.h

@@ -79,6 +79,16 @@ void nf_log_packet(struct net *net,
 		   const struct nf_loginfo *li,
 		   const char *fmt, ...);
 
+__printf(8, 9)
+void nf_log_trace(struct net *net,
+		  u_int8_t pf,
+		  unsigned int hooknum,
+		  const struct sk_buff *skb,
+		  const struct net_device *in,
+		  const struct net_device *out,
+		  const struct nf_loginfo *li,
+		  const char *fmt, ...);
+
 struct nf_log_buf;
 
 struct nf_log_buf *nf_log_buf_open(void);

net/ipv4/netfilter/ip_tables.c

@@ -272,7 +272,7 @@ static void trace_packet(const struct sk_buff *skb,
 		    &chainname, &comment, &rulenum) != 0)
 			break;
 
-	nf_log_packet(net, AF_INET, hook, skb, in, out, &trace_loginfo,
+	nf_log_trace(net, AF_INET, hook, skb, in, out, &trace_loginfo,
 		     "TRACE: %s:%s:%s:%u ",
 		     tablename, chainname, comment, rulenum);
 }

net/ipv6/netfilter/ip6_tables.c

@@ -298,7 +298,7 @@ static void trace_packet(const struct sk_buff *skb,
 		    &chainname, &comment, &rulenum) != 0)
 			break;
 
-	nf_log_packet(net, AF_INET6, hook, skb, in, out, &trace_loginfo,
+	nf_log_trace(net, AF_INET6, hook, skb, in, out, &trace_loginfo,
 		     "TRACE: %s:%s:%s:%u ",
 		     tablename, chainname, comment, rulenum);
 }

net/netfilter/nf_log.c

@@ -212,6 +212,30 @@ void nf_log_packet(struct net *net,
 }
 EXPORT_SYMBOL(nf_log_packet);
 
+void nf_log_trace(struct net *net,
+		  u_int8_t pf,
+		  unsigned int hooknum,
+		  const struct sk_buff *skb,
+		  const struct net_device *in,
+		  const struct net_device *out,
+		  const struct nf_loginfo *loginfo, const char *fmt, ...)
+{
+	va_list args;
+	char prefix[NF_LOG_PREFIXLEN];
+	const struct nf_logger *logger;
+
+	rcu_read_lock();
+	logger = rcu_dereference(net->nf.nf_loggers[pf]);
+	if (logger) {
+		va_start(args, fmt);
+		vsnprintf(prefix, sizeof(prefix), fmt, args);
+		va_end(args);
+		logger->logfn(net, pf, hooknum, skb, in, out, loginfo, prefix);
+	}
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL(nf_log_trace);
+
 #define S_SIZE (1024 - (sizeof(unsigned int) + 1))
 
 struct nf_log_buf {

net/netfilter/nf_tables_core.c

@@ -94,7 +94,7 @@ static void nft_trace_packet(const struct nft_pktinfo *pkt,
 {
 	struct net *net = dev_net(pkt->in ? pkt->in : pkt->out);
 
-	nf_log_packet(net, pkt->xt.family, pkt->ops->hooknum, pkt->skb, pkt->in,
+	nf_log_trace(net, pkt->xt.family, pkt->ops->hooknum, pkt->skb, pkt->in,
 		     pkt->out, &trace_loginfo, "TRACE: %s:%s:%s:%u ",
 		     chain->table->name, chain->name, comments[type],
 		     rulenum);