[ovs-dev] [PATCH branch-2.9] flow: Support extra padding length.

[Ilya Maximets]

From: Flavio Leitner <fbl at sysclose.org>

Although not required, padding can be optionally added until
the packet length is MTU bytes. A packet with extra padding
currently fails sanity checks.

Vulnerability: CVE-2020-35498
Fixes: fa8d9001a624 ("miniflow_extract: Properly handle small IP packets.")
Reported-by: Joakim Hindersson <joakim.hindersson at elastx.se>
Acked-by: Ilya Maximets <i.maximets at ovn.org>
Signed-off-by: Flavio Leitner <fbl at sysclose.org>
Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
---
 lib/conntrack.c     |  2 +-
 lib/dp-packet.h     | 10 +++++-----
 lib/flow.c          |  5 ++---
 tests/classifier.at | 36 ++++++++++++++++++++++++++++++++++++
 4 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/lib/conntrack.c b/lib/conntrack.c
index f7d0aa68f..e45ec18f6 100644
--- a/lib/conntrack.c
+++ b/lib/conntrack.c
@@ -640,7 +640,7 @@ static void
 reverse_nat_packet(struct dp_packet *pkt, const struct conn *conn)
 {
     char *tail = dp_packet_tail(pkt);
-    uint8_t pad = dp_packet_l2_pad_size(pkt);
+    uint16_t pad = dp_packet_l2_pad_size(pkt);
     struct conn_key inner_key;
     const char *inner_l4 = NULL;
     uint16_t orig_l3_ofs = pkt->l3_ofs;
diff --git a/lib/dp-packet.h b/lib/dp-packet.h
index b3a86ccf0..9d95b902d 100644
--- a/lib/dp-packet.h
+++ b/lib/dp-packet.h
@@ -65,7 +65,7 @@ struct dp_packet {
 
     /* All the following elements of this struct are copied in a single call
      * of memcpy in dp_packet_clone_with_headroom. */
-    uint8_t l2_pad_size;           /* Detected l2 padding size.
+    uint16_t l2_pad_size;          /* Detected l2 padding size.
                                     * Padding is non-pullable. */
     uint16_t l2_5_ofs;             /* MPLS label stack offset, or UINT16_MAX */
     uint16_t l3_ofs;               /* Network-level header offset,
@@ -95,8 +95,8 @@ void *dp_packet_resize_l2(struct dp_packet *, int increment);
 void *dp_packet_resize_l2_5(struct dp_packet *, int increment);
 static inline void *dp_packet_eth(const struct dp_packet *);
 static inline void dp_packet_reset_offsets(struct dp_packet *);
-static inline uint8_t dp_packet_l2_pad_size(const struct dp_packet *);
-static inline void dp_packet_set_l2_pad_size(struct dp_packet *, uint8_t);
+static inline uint16_t dp_packet_l2_pad_size(const struct dp_packet *);
+static inline void dp_packet_set_l2_pad_size(struct dp_packet *, uint16_t);
 static inline void *dp_packet_l2_5(const struct dp_packet *);
 static inline void dp_packet_set_l2_5(struct dp_packet *, void *);
 static inline void *dp_packet_l3(const struct dp_packet *);
@@ -295,14 +295,14 @@ dp_packet_reset_offsets(struct dp_packet *b)
     b->l4_ofs = UINT16_MAX;
 }
 
-static inline uint8_t
+static inline uint16_t
 dp_packet_l2_pad_size(const struct dp_packet *b)
 {
     return b->l2_pad_size;
 }
 
 static inline void
-dp_packet_set_l2_pad_size(struct dp_packet *b, uint8_t pad_size)
+dp_packet_set_l2_pad_size(struct dp_packet *b, uint16_t pad_size)
 {
     ovs_assert(pad_size <= dp_packet_size(b));
     b->l2_pad_size = pad_size;
diff --git a/lib/flow.c b/lib/flow.c
index e7fc574fd..551908bdb 100644
--- a/lib/flow.c
+++ b/lib/flow.c
@@ -763,7 +763,7 @@ miniflow_extract(struct dp_packet *packet, struct miniflow *dst)
         if (OVS_UNLIKELY(tot_len > size || ip_len > tot_len)) {
             goto out;
         }
-        if (OVS_UNLIKELY(size - tot_len > UINT8_MAX)) {
+        if (OVS_UNLIKELY(size - tot_len > UINT16_MAX)) {
             goto out;
         }
         dp_packet_set_l2_pad_size(packet, size - tot_len);
@@ -807,8 +807,7 @@ miniflow_extract(struct dp_packet *packet, struct miniflow *dst)
         if (OVS_UNLIKELY(plen > size)) {
             goto out;
         }
-        /* Jumbo Payload option not supported yet. */
-        if (OVS_UNLIKELY(size - plen > UINT8_MAX)) {
+        if (OVS_UNLIKELY(size - plen > UINT16_MAX)) {
             goto out;
         }
         dp_packet_set_l2_pad_size(packet, size - plen);
diff --git a/tests/classifier.at b/tests/classifier.at
index 2362948e3..350aadfc6 100644
--- a/tests/classifier.at
+++ b/tests/classifier.at
@@ -306,3 +306,39 @@ ovs-ofctl: Incorrect instruction ordering
 ])
 OVS_VSWITCHD_STOP
 AT_CLEANUP
+
+# Flow classifier a packet with excess of padding.
+AT_SETUP([flow classifier - packet with extra padding])
+OVS_VSWITCHD_START
+add_of_ports br0 1 2
+AT_DATA([flows.txt], [dnl
+priority=5,ip,ip_dst=1.1.1.1,actions=1
+priority=5,ip,ip_dst=1.1.1.2,actions=2
+priority=0,actions=drop
+])
+AT_CHECK([ovs-ofctl add-flows br0 flows.txt])
+packet=00020202020000010101010008004500001c00010000401176cc01010101010101020d6a00350008ee3a
+AT_CHECK([ovs-appctl ofproto/trace br0 in_port=1 $packet] , [0], [stdout])
+AT_CHECK([tail -2 stdout], [0],
+  [Megaflow: recirc_id=0,eth,ip,in_port=1,nw_dst=1.1.1.2,nw_frag=no
+Datapath actions: 2
+])
+# normal packet plus 255 bytes of padding (8bit padding).
+# 255 * 2 = 510
+padding=$(printf '%*s' 510 | tr ' ' '0')
+AT_CHECK([ovs-appctl ofproto/trace br0 in_port=1 ${packet}${padding}] , [0], [stdout])
+AT_CHECK([tail -2 stdout], [0],
+  [Megaflow: recirc_id=0,eth,ip,in_port=1,nw_dst=1.1.1.2,nw_frag=no
+Datapath actions: 2
+])
+# normal packet plus padding up to 65535 bytes of length (16bit limit).
+# 65535 - 43 = 65492
+# 65492 * 2 = 130984
+padding=$(printf '%*s' 130984 | tr ' ' '0')
+AT_CHECK([ovs-appctl ofproto/trace br0 in_port=1 ${packet}${padding}], [0], [stdout])
+AT_CHECK([tail -2 stdout], [0],
+  [Megaflow: recirc_id=0,eth,ip,in_port=1,nw_dst=1.1.1.2,nw_frag=no
+Datapath actions: 2
+])
+OVS_VSWITCHD_STOP
+AT_CLEANUP
-- 
2.26.2