tun_metadata: Fix coredump caused by use-after-free bug

Tun_metadata can be referened by flow and frozen_state at the same
time. When ovs-vswitchd handles TLV table mod message, the involved
tun_metadata gets freed. The call trace to free tun_metadata is
shown as below:

ofproto_run
- handle_openflow
  - handle_single_part_openflow
    - handle_tlv_table_mod
      - tun_metadata_table_mod
        - tun_metadata_postpone_free

Unfortunately, this tun_metadata can be still used by some frozen_state,
and later on when frozen_state tries to access its tun_metadata table,
ovs-vswitchd crashes. The call trace to access tun_metadata from
frozen_state is shown as below:

udpif_upcall_handler
- recv_upcalls
  - process_upcall
    - frozen_metadata_to_flow

It is unsafe for frozen_state to reference tun_table because tun_table
is protected by RCU while the lifecycle of frozen_state can span several
RCU quiesce states. Current code violates OVS's RCU protection mechanism.

This patch fixes it by simply stopping frozen_state from referencing
tun_table. If frozen_state needs tun_table, the latest valid tun_table
can be found through ofproto_get_tun_tab() efficiently.

A previous commit seems fixing the samiliar issue:
254878c18874f6 (ofproto-dpif-xlate: Fix segmentation fault caused by tun_table)

VMware-BZ: #2526222
Signed-off-by: Yifeng Sun <pkusunyifeng@gmail.com>
Signed-off-by: William Tu <u9012063@gmail.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/ofproto/ofproto-dpif-rid.h b/ofproto/ofproto-dpif-rid.h
index e5d02caf2..30cd5275f 100644
--- a/ofproto/ofproto-dpif-rid.h
+++ b/ofproto/ofproto-dpif-rid.h
@@ -22,6 +22,7 @@
 
 #include "cmap.h"
 #include "ofproto-dpif-mirror.h"
+#include "ofproto/ofproto-provider.h"
 #include "openvswitch/list.h"
 #include "openvswitch/ofp-actions.h"
 #include "ovs-thread.h"
@@ -115,16 +116,25 @@ frozen_metadata_from_flow(struct frozen_metadata *md,
 {
     memset(md, 0, sizeof *md);
     md->tunnel = flow->tunnel;
+    /* It is unsafe for frozen_state to reference tun_table because
+     * tun_table is protected by RCU while the lifecycle of frozen_state
+     * can span several RCU quiesce states.
+     *
+     * The latest valid tun_table can be found by ofproto_get_tun_tab()
+     * efficiently. */
+    md->tunnel.metadata.tab = NULL;
     md->metadata = flow->metadata;
     memcpy(md->regs, flow->regs, sizeof md->regs);
     md->in_port = flow->in_port.ofp_port;
 }
 
 static inline void
-frozen_metadata_to_flow(const struct frozen_metadata *md,
+frozen_metadata_to_flow(struct ofproto *ofproto,
+                        const struct frozen_metadata *md,
                         struct flow *flow)
 {
     flow->tunnel = md->tunnel;
+    flow->tunnel.metadata.tab = ofproto_get_tun_tab(ofproto);
     flow->metadata = md->metadata;
     memcpy(flow->regs, md->regs, sizeof flow->regs);
     flow->in_port.ofp_port = md->in_port;