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, 2 insertions, 1 deletions

diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
index 8dfa05b71..5e08ef10d 100644
--- a/ofproto/ofproto-dpif-upcall.c
+++ b/ofproto/ofproto-dpif-upcall.c
@@ -1534,7 +1534,8 @@ process_upcall(struct udpif *udpif, struct upcall *upcall,
                 flow_clear_conntrack(&frozen_flow);
             }
 
-            frozen_metadata_to_flow(&state->metadata, &frozen_flow);
+            frozen_metadata_to_flow(&upcall->ofproto->up, &state->metadata,
+                                    &frozen_flow);
             flow_get_metadata(&frozen_flow, &am->pin.up.base.flow_metadata);
 
             ofproto_dpif_send_async_msg(upcall->ofproto, am);