[PATCH 1/2] netfilter: nf_conntrack_irc: Tighten matching on DCC message

[PATCH 1/2] netfilter: nf_conntrack_irc: Tighten matching on DCC message

[David Leadbeater]

CTCP messages should only be at the start of an IRC message, not
anywhere within it.

Fixes: 869f37d8 ("[NETFILTER]: nf_conntrack/nf_nat: add IRC helper port")
Signed-off-by: David Leadbeater <dgl@dgl.cx>
---
 net/netfilter/nf_conntrack_irc.c | 34 ++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nf_conntrack_irc.c b/net/netfilter/nf_conntrack_irc.c
index 1796c456ac98..3b9d6f8ba436 100644
--- a/net/netfilter/nf_conntrack_irc.c
+++ b/net/netfilter/nf_conntrack_irc.c
@@ -157,15 +157,37 @@ static int help(struct sk_buff *skb, unsigned int protoff,
 	data = ib_ptr;
 	data_limit = ib_ptr + datalen;
 
-	/* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
-	 * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
-	while (data < data_limit - (19 + MINMATCHLEN)) {
-		if (memcmp(data, "\1DCC ", 5)) {
+	/* Skip any whitespace */
+	while (data < data_limit - 10) {
+		if (*data == ' ' || *data == '\r' || *data == '\n')
+			data++;
+		else
+			break;
+	}
+
+	/* strlen("PRIVMSG x ")=10 */
+	if (data < data_limit - 10) {
+		if (strncasecmp("PRIVMSG ", data, 8))
+			goto out;
+		data += 8;
+	}
+
+	/* strlen(" :\1DCC SENT t AAAAAAAA P\1\n")=26
+	 * 7+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=26
+	 */
+	while (data < data_limit - (21 + MINMATCHLEN)) {
+		/* Find first " :", the start of message */
+		if (memcmp(data, " :", 2)) {
 			data++;
 			continue;
 		}
+		data += 2;
+
+		/* then check that place only for the DCC command */
+		if (memcmp(data, "\1DCC ", 5))
+			goto out;
 		data += 5;
-		/* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
+		/* we have at least (21+MINMATCHLEN)-(2+5) bytes valid data left */
 
 		iph = ip_hdr(skb);
 		pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
@@ -181,7 +203,7 @@ static int help(struct sk_buff *skb, unsigned int protoff,
 			pr_debug("DCC %s detected\n", dccprotos[i]);
 
 			/* we have at least
-			 * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
+			 * (21+MINMATCHLEN)-7-dccprotos[i].matchlen bytes valid
 			 * data left (== 14/13 bytes) */
 			if (parse_dcc(data, data_limit, &dcc_ip,
 				       &dcc_port, &addr_beg_p, &addr_end_p)) {
-- 
2.37.1

[PATCH 2/2] netfilter: nf_conntrack_irc: Fix forged IP logic

[David Leadbeater]

Ensure the match happens in the right direction, previously the
destination used was the server, not the NAT host, as the comment
shows the code intended.

Additionally nf_nat_irc uses port 0 as a signal and there's no valid way
it can appear in a DCC message, so consider port 0 also forged.

Fixes: 869f37d8 ("[NETFILTER]: nf_conntrack/nf_nat: add IRC helper port")
Signed-off-by: David Leadbeater <dgl@dgl.cx>
---
 net/netfilter/nf_conntrack_irc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_irc.c b/net/netfilter/nf_conntrack_irc.c
index 3b9d6f8ba436..5703846bea3b 100644
--- a/net/netfilter/nf_conntrack_irc.c
+++ b/net/netfilter/nf_conntrack_irc.c
@@ -216,8 +216,9 @@ static int help(struct sk_buff *skb, unsigned int protoff,
 
 			/* dcc_ip can be the internal OR external (NAT'ed) IP */
 			tuple = &ct->tuplehash[dir].tuple;
-			if (tuple->src.u3.ip != dcc_ip &&
-			    tuple->dst.u3.ip != dcc_ip) {
+			if ((tuple->src.u3.ip != dcc_ip &&
+			     ct->tuplehash[!dir].tuple.dst.u3.ip != dcc_ip) ||
+			    dcc_port == 0) {
 				net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 						     &tuple->src.u3.ip,
 						     &dcc_ip, dcc_port);
-- 
2.37.1

Re: [PATCH 2/2] netfilter: nf_conntrack_irc: Fix forged IP logic

[Pablo Neira Ayuso]

On Fri, Aug 26, 2022 at 02:56:58PM +1000, David Leadbeater wrote:
> Ensure the match happens in the right direction, previously the
> destination used was the server, not the NAT host, as the comment
> shows the code intended.
> 
> Additionally nf_nat_irc uses port 0 as a signal and there's no valid way
> it can appear in a DCC message, so consider port 0 also forged.

Applied, thanks