releases/4.4.8/ax25-add-link-layer-header-validation-function.patch

From foo@baz Sat Apr 16 10:02:53 PDT 2016
From: Willem de Bruijn <willemb@google.com>
Date: Wed, 9 Mar 2016 21:58:33 -0500
Subject: ax25: add link layer header validation function

From: Willem de Bruijn <willemb@google.com>

[ Upstream commit ea47781c26510e5d97f80f9aceafe9065bd5e3aa ]

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@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ax25/ax25_ip.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/net/ax25/ax25_ip.c
+++ b/net/ax25/ax25_ip.c
@@ -228,8 +228,23 @@ netdev_tx_t ax25_ip_xmit(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,
+	.validate = ax25_validate_header,
 };
 
 EXPORT_SYMBOL(ax25_header_ops);