netfilter: conntrack_irc: fix possible out-of-bounds read

[ Upstream commit 66eba0ffce3b7e11449946b4cbbef8ea36112f56 ]

When parsing fails after we've matched the command string we
should bail out instead of trying to match a different command.

This helper should be deprecated, given prevalence of TLS I doubt it has
any relevance in 2026.

Fixes: 869f37d8e4 ("[NETFILTER]: nf_conntrack/nf_nat: add IRC helper port")
Closes: https://sashiko.dev/#/patchset/20260525182924.28456-1-fw%40strlen.de
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Ulrich Hecht <uli@kernel.org>

net/netfilter/nf_conntrack_irc.c

@@ -201,7 +201,7 @@ static int help(struct sk_buff *skb, unsigned int protoff,
 			if (parse_dcc(data, data_limit, &dcc_ip,
 				       &dcc_port, &addr_beg_p, &addr_end_p)) {
 				pr_debug("unable to parse dcc command\n");
-				continue;
+				goto out;
 			}
 
 			pr_debug("DCC bound ip/port: %pI4:%u\n",
@@ -215,7 +215,7 @@ static int help(struct sk_buff *skb, unsigned int protoff,
 				net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 						     &tuple->src.u3.ip,
 						     &dcc_ip, dcc_port);
-				continue;
+				goto out;
 			}
 
 			exp = nf_ct_expect_alloc(ct);