ofp-ed-props: Fix using uninitialized padding for NSH encap actions.

OVS uses memcmp to compare actions of existing and new flows, but
'struct ofp_ed_prop_nsh_md_type' and corresponding ofpact structure has
3 bytes of padding that never initialized and passed around within OF
data structures and messages.

  Uninitialized bytes in MemcmpInterceptorCommon
    at offset 21 inside [0x7090000003f8, 136)
  WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x4a184e in bcmp (vswitchd/ovs-vswitchd+0x4a184e)
    #1 0x896c8a in ofpacts_equal lib/ofp-actions.c:9121:31
    #2 0x564403 in replace_rule_finish ofproto/ofproto.c:5650:37
    #3 0x563462 in add_flow_finish ofproto/ofproto.c:5218:13
    #4 0x54a1ff in ofproto_flow_mod_finish ofproto/ofproto.c:8091:17
    #5 0x5433b2 in handle_flow_mod__ ofproto/ofproto.c:6216:17
    #6 0x56a2fc in handle_flow_mod ofproto/ofproto.c:6190:17
    #7 0x565bda in handle_single_part_openflow ofproto/ofproto.c:8504:16
    #8 0x540b25 in handle_openflow ofproto/ofproto.c:8685:21
    #9 0x6697fd in ofconn_run ofproto/connmgr.c:1329:13
    #10 0x668e6e in connmgr_run ofproto/connmgr.c:356:9
    #11 0x53f1bc in ofproto_run ofproto/ofproto.c:1890:5
    #12 0x4ead0c in bridge_run__ vswitchd/bridge.c:3250:9
    #13 0x4e9bc8 in bridge_run vswitchd/bridge.c:3309:5
    #14 0x51c072 in main vswitchd/ovs-vswitchd.c:127:9
    #15 0x7f23a99011a2 in __libc_start_main (/lib64/libc.so.6)
    #16 0x46b92d in _start (vswitchd/ovs-vswitchd+0x46b92d)

  Uninitialized value was stored to memory at
    #0 0x4745aa in __msan_memcpy.part.0 (vswitchd/ovs-vswitchd)
    #1 0x54529f in rule_actions_create ofproto/ofproto.c:3134:5
    #2 0x54915e in ofproto_rule_create ofproto/ofproto.c:5284:11
    #3 0x55d419 in add_flow_init ofproto/ofproto.c:5123:17
    #4 0x54841f in ofproto_flow_mod_init ofproto/ofproto.c:7987:17
    #5 0x543250 in handle_flow_mod__ ofproto/ofproto.c:6206:13
    #6 0x56a2fc in handle_flow_mod ofproto/ofproto.c:6190:17
    #7 0x565bda in handle_single_part_openflow ofproto/ofproto.c:8504:16
    #8 0x540b25 in handle_openflow ofproto/ofproto.c:8685:21
    #9 0x6697fd in ofconn_run ofproto/connmgr.c:1329:13
    #10 0x668e6e in connmgr_run ofproto/connmgr.c:356:9
    #11 0x53f1bc in ofproto_run ofproto/ofproto.c:1890:5
    #12 0x4ead0c in bridge_run__ vswitchd/bridge.c:3250:9
    #13 0x4e9bc8 in bridge_run vswitchd/bridge.c:3309:5
    #14 0x51c072 in main vswitchd/ovs-vswitchd.c:127:9
    #15 0x7f23a99011a2 in __libc_start_main (/lib64/libc.so.6)

  Uninitialized value was created by an allocation of 'ofpacts_stub'
  in the stack frame of function 'handle_flow_mod'
    #0 0x569e80 in handle_flow_mod ofproto/ofproto.c:6170

This could cause issues with flow modifications or other operations.

To reproduce, some NSH tests could be run under valgrind or clang
MemorySantizer. Ex. "nsh - md1 encap over a veth link" test.

Fix that by clearing padding bytes while encoding and decoding.
OVS will still accept OF messages with non-zero padding from
controllers.

New tests added to tests/ofp-actions.at.

Fixes: 1fc11c5 ("Generic encap and decap support for NSH")
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Jan Scheurich <jan.scheurich@ericsson.com>

lib/ofp-ed-props.c

@@ -49,7 +49,7 @@ decode_ed_prop(const struct ofp_ed_prop_header **ofp_prop,
                 return OFPERR_NXBAC_BAD_ED_PROP;
             }
             struct ofpact_ed_prop_nsh_md_type *pnmt =
-                    ofpbuf_put_uninit(out, sizeof(*pnmt));
+                    ofpbuf_put_zeros(out, sizeof *pnmt);
             pnmt->header.prop_class = prop_class;
             pnmt->header.type = prop_type;
             pnmt->header.len = len;
@@ -108,6 +108,7 @@ encode_ed_prop(const struct ofpact_ed_prop **prop,
             opnmt->header.len =
                     offsetof(struct ofp_ed_prop_nsh_md_type, pad);
             opnmt->md_type = pnmt->md_type;
+            memset(opnmt->pad, 0, sizeof opnmt->pad);
             prop_len = sizeof(*pnmt);
             break;
         }

tests/ofp-actions.at

@@ -769,6 +769,17 @@ dnl Check OpenFlow v1.3.4 Conformance Test: 430.510.
 & 00000010  00 00 00 10 00 00 00 01-
 0019 0010 80000807 000102030405 000000000010 00000001
 
+dnl Check NSH encap (experimenter extension).
+# actions=encap(nsh(md_type=1))
+ffff 0018 00002320 002e 0000 0001894f 0004 01 05 01 000000
+
+dnl NSH encap with non-zero padding.
+# actions=encap(nsh(md_type=1))
+# 21: 12 -> 00
+# 22: 34 -> 00
+# 23: 56 -> 00
+ffff 0018 00002320 002e 0000 0001894f 0004 01 05 01 123456
+
 ])
 sed '/^[[#&]]/d' < test-data > input.txt
 sed -n 's/^# //p; /^$/p' < test-data > expout