[PATCH nf-next v5 2/4] netfilter: nf_conntrack_irc: use nf_ct_helper_parse_port()

[Rahul Chandelkar <rc@rexion.ai>]

parse_dcc() stores the result of simple_strtoul() directly into the u16
*port, so a DCC port above 65535 is silently truncated (e.g. 65537
becomes 1) and a conntrack expectation is created for a port that never
appeared in the DCC command.

Use nf_ct_helper_parse_port(), which parses the length-delimited buffer
without relying on NUL termination and rejects port 0, values above
65535 and digit runs longer than five characters.

Since parse_dcc() now fails for port 0, the dcc_port == 0 test in help()
can no longer be true; remove it.  A DCC command with port 0 is now
dropped through the "unable to parse dcc command" debug path instead of
the ratelimited "Forged DCC command" warning; no expectation is created
in either case.

Build-tested with allmodconfig and allyesconfig (W=1) and sparse, and
cross-built for i386 and big-endian powerpc.  It has not
been run-time tested with IRC traffic.

Fixes: 869f37d8e48f ("[NETFILTER]: nf_conntrack/nf_nat: add IRC helper port")
Assisted-by: Claude-Code:claude-opus-5-5 sparse
Signed-off-by: Rahul Chandelkar <rc@rexion.ai>
---
 net/netfilter/nf_conntrack_irc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_conntrack_irc.c b/net/netfilter/nf_conntrack_irc.c
index 92360963757a..88c4530c4841 100644
--- a/net/netfilter/nf_conntrack_irc.c
+++ b/net/netfilter/nf_conntrack_irc.c
@@ -88,7 +88,9 @@ static int parse_dcc(char *data, const char *data_end, __be32 *ip,
 		data++;
 	}
 
-	*port = simple_strtoul(data, &data, 10);
+	if (nf_ct_helper_parse_port(data, data_end - data, port, &data))
+		return -1;
+
 	*ad_end_p = data;
 
 	return 0;
@@ -206,9 +208,8 @@ 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 &&
-			     ct->tuplehash[!dir].tuple.dst.u3.ip != dcc_ip) ||
-			    dcc_port == 0) {
+			if (tuple->src.u3.ip != dcc_ip &&
+			    ct->tuplehash[!dir].tuple.dst.u3.ip != dcc_ip) {
 				net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 						     &tuple->src.u3.ip,
 						     &dcc_ip, dcc_port);
-- 
2.43.0