From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 18 Jan 2018 19:18:14 +0000 (-0500)
Subject: Fix: network instrumentation handling of corrupted TCP headers
X-Git-Tag: v2.11.0-rc1~82
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=0910ab71db3c3f618edae89ec46fe9b7487c7eac;p=lttng-modules.git

Fix: network instrumentation handling of corrupted TCP headers

A malformed packet may contain a valid IPv4/IPv6 header, but an
inconsistent TCP header. As a result, the trace contains a fully
formed IPv4/IPv6 header, including the "protocol" or "nexthdr"
fields indicating TCP, but no following TCP header.

This scenario leads to an unreadable CTF trace, because the
trace viewer expects a TCP header, but instead gets the next
event.

Therefore, using the IP header fields as selector for the
transport layer variant is not the right approach: introduce
our own selector field, which allows to properly deal with this
corner-case.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/instrumentation/events/lttng-module/net.h b/instrumentation/events/lttng-module/net.h
index 19a22a84..e48c4db1 100644
--- a/instrumentation/events/lttng-module/net.h
+++ b/instrumentation/events/lttng-module/net.h
@@ -104,11 +104,11 @@ static struct lttng_event_field transport_fields[] = {
 };
 
 enum transport_header_types {
-	TH_NONE,
-	TH_TCP,
+	TH_NONE = 0,
+	TH_TCP = 1,
 };
 
-static inline unsigned char __get_transport_header_type(struct sk_buff *skb)
+static inline enum transport_header_types __get_transport_header_type(struct sk_buff *skb)
 {
 	if (__has_network_hdr(skb)) {
 		/*
@@ -135,20 +135,15 @@ static inline unsigned char __get_transport_header_type(struct sk_buff *skb)
 
 static struct lttng_enum_entry transport_enum_entries[] = {
 	[0] = {
-		.start = { .value = 0, .signedness = 0, },
-		.end = { .value = IPPROTO_TCP - 1, .signedness = 0, },
+		.start = { .value = TH_NONE, .signedness = 0, },
+		.end = { .value = TH_NONE, .signedness = 0, },
 		.string = "_unknown",
 	},
 	[1] = {
-		.start = { .value = IPPROTO_TCP, .signedness = 0, },
-		.end = { .value = IPPROTO_TCP, .signedness = 0, },
+		.start = { .value = TH_TCP, .signedness = 0, },
+		.end = { .value = TH_TCP, .signedness = 0, },
 		.string = "_tcp",
 	},
-	[2] = {
-		.start = { .value = IPPROTO_TCP + 1, .signedness = 0, },
-		.end = { .value = 255, .signedness = 0, },
-		.string = "_unknown",
-	},
 };
 
 static const struct lttng_enum_desc transport_header_type = {
@@ -239,10 +234,25 @@ static struct lttng_event_field ipv4fields[] = {
 		},
 	},
 	[11] = {
+		.name = "transport_header_type",
+		.type = {
+			.atype = atype_enum,
+			.u.basic.enumeration.desc = &transport_header_type,
+			.u.basic.enumeration.container_type = {
+				.size = 8,
+				.alignment = 8,
+				.signedness = 0,
+				.reverse_byte_order = 0,
+				.base = 10,
+				.encoding = lttng_encode_none,
+			},
+		},
+	},
+	[12] = {
 		.name = "transport_header",
 		.type = {
 			.atype = atype_variant,
-			.u.variant.tag_name = "protocol",
+			.u.variant.tag_name = "transport_header_type",
 			.u.variant.choices = transport_fields,
 			.u.variant.nr_choices = ARRAY_SIZE(transport_fields),
 		},
@@ -320,10 +330,25 @@ static struct lttng_event_field ipv6fields[] = {
 		},
 	},
 	[8] = {
+		.name = "transport_header_type",
+		.type = {
+			.atype = atype_enum,
+			.u.basic.enumeration.desc = &transport_header_type,
+			.u.basic.enumeration.container_type = {
+				.size = 8,
+				.alignment = 8,
+				.signedness = 0,
+				.reverse_byte_order = 0,
+				.base = 10,
+				.encoding = lttng_encode_none,
+			},
+		},
+	},
+	[9] = {
 		.name = "transport_header",
 		.type = {
 			.atype = atype_variant,
-			.u.variant.tag_name = "nexthdr",
+			.u.variant.tag_name = "transport_header_type",
 			.u.variant.choices = transport_fields,
 			.u.variant.nr_choices = ARRAY_SIZE(transport_fields),
 		},
@@ -436,18 +461,22 @@ LTTNG_TRACEPOINT_EVENT_CLASS(net_dev_template,
 			),
 			network_header,
 			ctf_custom_code(
+				bool has_network_header = false;
+
 				/* Copy the network header. */
 				switch (__get_network_header_type(skb)) {
 				case NH_IPV4: {
 					ctf_align(uint16_t)
 					ctf_array_type(uint8_t, ip_hdr(skb),
 							sizeof(struct iphdr))
+					has_network_header = true;
 					break;
 				}
 				case NH_IPV6: {
 					ctf_align(uint16_t)
 					ctf_array_type(uint8_t, ipv6_hdr(skb),
 							sizeof(struct ipv6hdr))
+					has_network_header = true;
 					break;
 				}
 				default:
@@ -458,17 +487,24 @@ LTTNG_TRACEPOINT_EVENT_CLASS(net_dev_template,
 					break;
 				}
 
-				/* Copy the transport header. */
-				if (__get_transport_header_type(skb)
-						== TH_TCP) {
-					ctf_align(uint32_t)
-					ctf_array_type(uint8_t, tcp_hdr(skb),
-							sizeof(struct tcphdr))
+				if (has_network_header) {
+					enum transport_header_types th_type =
+						__get_transport_header_type(skb);
+
+					/* Transport header type field. */
+					ctf_integer_type(unsigned char, th_type)
+
+					/* Copy the transport header. */
+					if (th_type == TH_TCP) {
+						ctf_align(uint32_t)
+						ctf_array_type(uint8_t, tcp_hdr(skb),
+								sizeof(struct tcphdr))
+					}
+					/*
+					 * For any other transport header type,
+					 * there is nothing to do.
+					 */
 				}
-				/*
-				 * For any other transport header type,
-				 * there is nothing to do.
-				 */
 			)
 		)
 	)