[PATCH nf-next v4 1/4] netfilter: conntrack: add shared uint and port parsers for helpers

[Rahul Chandelkar <rc@rexion.ai>]

Several conntrack helpers parse integers and port numbers out of
application-layer payload.  Some open-code simple_strtoul() (which
requires a NUL-terminated string and returns unsigned long without any
range check), while nf_conntrack_sip carries its own sip_strtouint().

Add two length-delimited parsers to the conntrack helper core so helpers
can share one implementation:

  nf_ct_helper_parse_uint() - bounded decimal parser that operates on an
    unterminated buffer, capping the result at UINT_MAX.  Its body is
    taken from sip_strtouint() so nf_conntrack_sip can drop its private
    copy in a later patch.

  nf_ct_helper_parse_port() - thin wrapper that parses a port and rejects
    zero and values above 65535.

Both are exported so the IRC, Amanda and SIP helpers can use them.

Signed-off-by: Rahul Chandelkar <rc@rexion.ai>
---
 include/net/netfilter/nf_conntrack_helper.h |  5 ++
 net/netfilter/nf_conntrack_helper.c         | 68 +++++++++++++++++++++
 2 files changed, 73 insertions(+)

diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
index 335b8c43694f..4d5ad5ae1d13 100644
--- a/include/net/netfilter/nf_conntrack_helper.h
+++ b/include/net/netfilter/nf_conntrack_helper.h
@@ -184,6 +184,11 @@ 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);
 
+unsigned int nf_ct_helper_parse_uint(const char *cp, unsigned int len,
+				     char **endp);
+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 c30ae3f203be..99b90a54d8a9 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -16,6 +16,7 @@
 #include <linux/random.h>
 #include <linux/err.h>
 #include <linux/kernel.h>
+#include <linux/ctype.h>
 #include <linux/netdevice.h>
 #include <linux/rculist.h>
 #include <linux/rtnetlink.h>
@@ -569,6 +570,73 @@ void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 }
 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 
+/* Parse a decimal unsigned integer from a length-delimited buffer that is not
+ * necessarily NUL-terminated.  At most @len bytes are examined.  On success
+ * the parsed value is returned and, if @endp is non-NULL, *@endp points just
+ * past the last digit consumed.  If no digit is found or the value would
+ * exceed UINT_MAX, 0 is returned and *@endp is set to @cp.
+ */
+unsigned int nf_ct_helper_parse_uint(const char *cp, unsigned int len,
+				     char **endp)
+{
+	const unsigned int max = sizeof("4294967295");
+	unsigned int olen = len;
+	const char *s = cp;
+	u64 result = 0;
+
+	if (len > max)
+		len = max;
+
+	while (olen > 0 && isdigit(*s)) {
+		unsigned int value;
+
+		if (len == 0)
+			goto err;
+
+		value = *s - '0';
+		result = result * 10 + value;
+
+		if (result > UINT_MAX)
+			goto err;
+		s++;
+		len--;
+		olen--;
+	}
+
+	if (endp)
+		*endp = (char *)s;
+
+	return result;
+err:
+	if (endp)
+		*endp = (char *)cp;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nf_ct_helper_parse_uint);
+
+/* Parse a TCP/UDP port (1-65535) from a length-delimited buffer using
+ * nf_ct_helper_parse_uint().  Returns 0 and stores the port in *@port (and the
+ * end pointer in *@endp) on success, or -1 if no digit is found or the value
+ * is out of range.
+ */
+int nf_ct_helper_parse_port(const char *cp, unsigned int len,
+			    u16 *port, char **endp)
+{
+	char *e = (char *)cp;
+	unsigned int val;
+
+	val = nf_ct_helper_parse_uint(cp, len, &e);
+	if (e == cp || val == 0 || val > 65535)
+		return -1;
+
+	*port = val;
+	if (endp)
+		*endp = e;
+
+	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 */
-- 
2.43.0