[PATCH net-next v2 1/3] netfilter: conntrack: add shared port parser for helpers

[HACKE-RC <rc@rexion.ai>]

Add nf_ct_helper_parse_port() to the conntrack helper core. This
provides a port parser that does not rely on nul-terminated strings,
taking an explicit length parameter and validating the result fits
in the 1-65535 range.

Modeled after the approach in 8cf6809cddcb ("netfilter:
nf_conntrack_sip: don't use simple_strtoul") but as a shared
function so IRC, Amanda, and other helpers can use it instead of
open-coding simple_strtoul calls with ad-hoc range checks.

Signed-off-by: HACKE-RC <rc@rexion.ai>
---
 include/net/netfilter/nf_conntrack_helper.h |  3 +++
 net/netfilter/nf_conntrack_helper.c         | 28 +++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
index de2f956ab..db19fe25f 100644
--- a/include/net/netfilter/nf_conntrack_helper.h
+++ b/include/net/netfilter/nf_conntrack_helper.h
@@ -160,6 +160,9 @@ nf_ct_helper_expectfn_find_by_name(const char *name);
 struct nf_ct_helper_expectfn *
 nf_ct_helper_expectfn_find_by_symbol(const void *symbol);
 
+int nf_ct_helper_parse_port(const char *cp, unsigned int len,
+			    u16 *port, char **endp);
+
 extern struct hlist_head *nf_ct_helper_hash;
 extern unsigned int nf_ct_helper_hsize;
 
diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index a715304a5..12f51670d 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -499,6 +499,34 @@ void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 }
 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 
+int nf_ct_helper_parse_port(const char *cp, unsigned int len,
+			    u16 *port, char **endp)
+{
+	unsigned long result = 0;
+	const char *start = cp;
+
+	while (len > 0 && *cp >= '0' && *cp <= '9') {
+		result = result * 10 + (*cp - '0');
+		if (result > 65535)
+			return -1;
+		cp++;
+		len--;
+	}
+
+	if (cp == start)
+		return -1;
+
+	if (result == 0)
+		return -1;
+
+	*port = result;
+	if (endp)
+		*endp = (char *)cp;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nf_ct_helper_parse_port);
+
 int nf_conntrack_helper_init(void)
 {
 	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
-- 
2.54.0