netlink: support legacy dump request messages

Some legacy tools, including iproute2 < 3.9, issue shorter RTM_GETLINK
and RTM_GETADDR dump queries which only contain struct rtgenmsg rather
than struct ifinfomsg. As noted in kernel comment in rtnl_dump_ifinfo(),
these legacy requests will be (even with attributes) always shorter than
struct ifinfomsg so that they are easy to detect.

Similar problem can be observed with tools using nl_rtgen_request()
function from libnl3; this also affects other RTM_GET* types.

If such legacy message is detected by length shorter than expected data
structure, parse it as this legacy version with (1-byte) struct
rtgenmsg so that it's shown as intended rather than as malformed.

Change-Id: I53b6bff9e44cd2359d7cd313b6f0724f63f0e74d
Reviewed-on: https://code.wireshark.org/review/20461
Petri-Dish: Michael Mann <mmann78@netscape.net>
Reviewed-by: Michal Kubeček <mkubecek@suse.cz>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>

1 files changed, 21 insertions, 0 deletions

diff --git a/epan/dissectors/packet-netlink-route.c b/epan/dissectors/packet-netlink-route.c
index 8e4c24564f..c00090e0e3 100644
--- a/epan/dissectors/packet-netlink-route.c
+++ b/epan/dissectors/packet-netlink-route.c
@@ -39,6 +39,7 @@ struct netlink_route_info {
 	struct packet_netlink_data *data;
 
 	int encoding; /* copy of data->encoding */
+	gboolean legacy;
 };
 
 enum {
@@ -411,6 +412,9 @@ dissect_netlink_route_ifinfomsg(tvbuff_t *tvb, struct netlink_route_info *info,
 	proto_tree_add_item(tree, &hfi_netlink_route_ifi_family, tvb, offset, 1, info->encoding);
 	offset += 1;
 
+	if (info->legacy)
+		return offset;
+
 	/* XXX padding, check if 0 */
 	offset += 1;
 
@@ -578,6 +582,9 @@ dissect_netlink_route_ifaddrmsg(tvbuff_t *tvb, struct netlink_route_info *info,
 	proto_tree_add_item(tree, &hfi_netlink_route_ifa_family,    tvb, offset, 1, ENC_NA);
 	offset += 1;
 
+	if (info->legacy)
+		return offset;
+
 	proto_tree_add_item(tree, &hfi_netlink_route_ifa_prefixlen, tvb, offset, 1, ENC_NA);
 	offset += 1;
 
@@ -731,6 +738,9 @@ dissect_netlink_route_rtmsg(tvbuff_t *tvb, struct netlink_route_info *info, prot
 	proto_tree_add_item(tree, &hfi_netlink_route_rt_family,   tvb, offset, 1, ENC_NA);
 	offset += 1;
 
+	if (info->legacy)
+		return offset;
+
 	proto_tree_add_item(tree, &hfi_netlink_route_rt_dst_len,  tvb, offset, 1, ENC_NA);
 	offset += 1;
 
@@ -877,6 +887,9 @@ dissect_netlink_route_ndmsg(tvbuff_t *tvb, struct netlink_route_info *info, prot
 	proto_tree_add_item(tree, &hfi_netlink_route_nd_family, tvb, offset, 1, ENC_NA);
 	offset += 1;
 
+	if (info->legacy)
+		return offset;
+
 	/* XXX, 3B padding */
 	offset += 3;
 
@@ -990,6 +1003,8 @@ dissect_netlink_route(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void
 		case WS_RTM_NEWLINK:
 		case WS_RTM_DELLINK:
 		case WS_RTM_GETLINK:
+			/* backward compatibility with legacy tools; 16 is sizeof(struct ifinfomsg) */
+			info.legacy = (data->type == WS_RTM_GETLINK) && (tvb_reported_length_remaining(tvb, offset) < 16);
 			offset = dissect_netlink_route_ifinfomsg(tvb, &info, tree, offset);
 			/* Optional attributes */
 			offset = dissect_netlink_route_attributes(tvb, &hfi_netlink_route_ifla_attr_type, &info, tree, offset, dissect_netlink_route_ifla_attrs);
@@ -998,6 +1013,8 @@ dissect_netlink_route(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void
 		case WS_RTM_NEWADDR:
 		case WS_RTM_DELADDR:
 		case WS_RTM_GETADDR:
+			/* backward compatibility with legacy tools; 8 is sizeof(struct ifaddrmsg) */
+			info.legacy = (data->type == WS_RTM_GETADDR) && (tvb_reported_length_remaining(tvb, offset) < 8);
 			offset = dissect_netlink_route_ifaddrmsg(tvb, &info, tree, offset);
 			/* Optional attributes */
 			offset = dissect_netlink_route_attributes(tvb, &hfi_netlink_route_ifa_attr_type, &info, tree, offset, dissect_netlink_route_ifa_attrs);
@@ -1006,6 +1023,8 @@ dissect_netlink_route(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void
 		case WS_RTM_NEWROUTE:
 		case WS_RTM_DELROUTE:
 		case WS_RTM_GETROUTE:
+			/* backward compatibility with legacy tools; 12 is sizeof(struct rtmsg) */
+			info.legacy = (data->type == WS_RTM_GETROUTE) && (tvb_reported_length_remaining(tvb, offset) < 12);
 			offset = dissect_netlink_route_rtmsg(tvb, &info, tree, offset);
 			/* Optional attributes */
 			offset = dissect_netlink_route_attributes(tvb, &hfi_netlink_route_rta_attr_type, &info, tree, offset, dissect_netlink_route_route_attrs);
@@ -1014,6 +1033,8 @@ dissect_netlink_route(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void
 		case WS_RTM_NEWNEIGH:
 		case WS_RTM_DELNEIGH:
 		case WS_RTM_GETNEIGH:
+			/* backward compatibility with legacy tools; 12 is sizeof(struct ndmsg) */
+			info.legacy = (data->type == WS_RTM_GETNEIGH) && (tvb_reported_length_remaining(tvb, offset) < 12);
 			offset = dissect_netlink_route_ndmsg(tvb, &info, tree, offset);
 			break;
 	}