net: Socket filter ancilliary data access for skb->dev->type

Add an SKF_AD_HATYPE field to the packet ancilliary data area, giving
access to skb->dev->type, as reported in the sll_hatype field.

When capturing packets on a PF_PACKET/SOCK_RAW socket bound to all
interfaces, there doesn't appear to be a way for the filter program to
actually find out the underlying hardware type the packet was captured
on. This patch adds such ability.

This patch also handles the case where skb->dev can be NULL, such as on
netlink sockets.

Signed-off-by: Paul Evans <leonerd@leonerd.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/filter.h

@@ -123,7 +123,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_NLATTR_NEST	16
 #define SKF_AD_MARK 	20
 #define SKF_AD_QUEUE	24
-#define SKF_AD_MAX	28
+#define SKF_AD_HATYPE	28
+#define SKF_AD_MAX	32
 #define SKF_NET_OFF   (-0x100000)
 #define SKF_LL_OFF    (-0x200000)
 

net/core/filter.c

@@ -302,6 +302,8 @@ load_b:
 			A = skb->pkt_type;
 			continue;
 		case SKF_AD_IFINDEX:
+			if (!skb->dev)
+				return 0;
 			A = skb->dev->ifindex;
 			continue;
 		case SKF_AD_MARK:
@@ -310,6 +312,11 @@ load_b:
 		case SKF_AD_QUEUE:
 			A = skb->queue_mapping;
 			continue;
+		case SKF_AD_HATYPE:
+			if (!skb->dev)
+				return 0;
+			A = skb->dev->type;
+			continue;
 		case SKF_AD_NLATTR: {
 			struct nlattr *nla;