[PATCH 3.16 202/217] ax25: add link layer header validation function

[Ben Hutchings]

3.16.35-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Willem de Bruijn <willemb@xxxxxxxxxx>

commit ea47781c26510e5d97f80f9aceafe9065bd5e3aa upstream.

As variable length protocol, AX25 fails link layer header validation
tests based on a minimum length. header_ops.validate allows protocols
to validate headers that are shorter than hard_header_len. Implement
this callback for AX25.

See also http://comments.gmane.org/gmane.linux.network/401064

Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/ax25/ax25_ip.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/net/ax25/ax25_ip.c
+++ b/net/ax25/ax25_ip.c
@@ -231,9 +231,24 @@ int ax25_rebuild_header(struct sk_buff *
 
 #endif
 
+static bool ax25_validate_header(const char *header, unsigned int len)
+{
+	ax25_digi digi;
+
+	if (!len)
+		return false;
+
+	if (header[0])
+		return true;
+
+	return ax25_addr_parse(header + 1, len - 1, NULL, NULL, &digi, NULL,
+			       NULL);
+}
+
 const struct header_ops ax25_header_ops = {
 	.create = ax25_hard_header,
 	.rebuild = ax25_rebuild_header,
+	.validate = ax25_validate_header,
 };
 
 EXPORT_SYMBOL(ax25_hard_header);