4.5-stable review patch.  If anyone has any objections, please let me know.

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

From: Willem de Bruijn <will...@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 <will...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@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);


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