[ovs-dev] [PATCH] conntrack: Correct length check for tcp packet inside ICMP data.

Vishal Deep Ajmera vishal.deep.ajmera at ericsson.com
Fri Aug 23 13:20:17 UTC 2019


An ICMP packet with type destination or host not reachable also carries
28 bytes of ICMP data field. This data field contains IP header and TCP
header (partial first 8 bytes) of the original packet for which ICMP
is being generated.

Conntrack module when processing these ICMP packets checks for TCP header
length (20 bytes). Since TCP header is partial the length check fails and
packet is erroneously dropped.

This patch fixes length check for TCP header when processing ICMP data
fields.

Signed-off-by: Vishal Deep Ajmera <vishal.deep.ajmera at ericsson.com>
---
 lib/conntrack.c | 14 +++++++++++---
 lib/packets.h   |  1 +
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/lib/conntrack.c b/lib/conntrack.c
index 5f60fea..0618fdd 100644
--- a/lib/conntrack.c
+++ b/lib/conntrack.c
@@ -1513,10 +1513,18 @@ check_l4_icmp6(const struct conn_key *key, const void *data, size_t size,
     return validate_checksum ? checksum_valid(key, data, size, l3) : true;
 }
 
+/* If related is NULL, we are parsing nested TCP header  inside ICMP packet.
+ * Only 8 bytes of TCP header is required by RFC to be present in such case.
+ */
 static inline bool
-extract_l4_tcp(struct conn_key *key, const void *data, size_t size)
+extract_l4_tcp(struct conn_key *key, const void *data, size_t size,
+               bool *related)
 {
-    if (OVS_UNLIKELY(size < TCP_HEADER_LEN)) {
+    if (!related) {
+        if (size < ICMP_L4_DATA_LEN) {
+            return false;
+        }
+    } else if (size < TCP_HEADER_LEN) {
         return false;
     }
 
@@ -1750,7 +1758,7 @@ extract_l4(struct conn_key *key, const void *data, size_t size, bool *related,
 {
     if (key->nw_proto == IPPROTO_TCP) {
         return (!related || check_l4_tcp(key, data, size, l3,
-                validate_checksum)) && extract_l4_tcp(key, data, size);
+              validate_checksum)) && extract_l4_tcp(key, data, size, related);
     } else if (key->nw_proto == IPPROTO_UDP) {
         return (!related || check_l4_udp(key, data, size, l3,
                 validate_checksum)) && extract_l4_udp(key, data, size);
diff --git a/lib/packets.h b/lib/packets.h
index a4bee38..2bc65c9 100644
--- a/lib/packets.h
+++ b/lib/packets.h
@@ -886,6 +886,7 @@ struct tcp_header {
     ovs_be16 tcp_urg;
 };
 BUILD_ASSERT_DECL(TCP_HEADER_LEN == sizeof(struct tcp_header));
+#define ICMP_L4_DATA_LEN 8
 
 /* Connection states.
  *
-- 
1.9.1



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