treewide: Don't pass NULL to library functions that expect non-NULL.

It's actually undefined behavior to pass NULL to standard library
functions that manipulate arrays (e.g., qsort, memcpy, memcmp), even if
the passed number of items is 0.

UB Sanitizer reports:
  ovsdb/monitor.c:408:9: runtime error: null pointer passed as argument 1,
                                        which is declared to never be null
      #0 0x406ae1 in ovsdb_monitor_columns_sort ovsdb/monitor.c:408
      #1 0x406ae1 in ovsdb_monitor_add ovsdb/monitor.c:1683
  [...]
  lib/ovsdb-data.c:1970:5: runtime error: null pointer passed as argument 2,
                                          which is declared to never be null
      #0 0x4071c8 in ovsdb_datum_push_unsafe lib/ovsdb-data.c:1970
      #1 0x471cd0 in ovsdb_datum_apply_diff_in_place lib/ovsdb-data.c:2345
  [...]
  ofproto/ofproto-dpif-rid.c:159:17:
        runtime error: null pointer passed as argument 1,
                       which is declared to never be null
      #0 0x4df5d8 in frozen_state_equal ofproto/ofproto-dpif-rid.c:159
      #1 0x4dfd27 in recirc_find_equal ofproto/ofproto-dpif-rid.c:179
      [...]

Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
Acked-by: Paolo Valerio <pvalerio@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

lib/dpif-netdev.c

@@ -5099,8 +5099,10 @@ dp_netdev_actions_create(const struct nlattr *actions, size_t size)
     struct dp_netdev_actions *netdev_actions;
 
     netdev_actions = xmalloc(sizeof *netdev_actions + size);
-    memcpy(netdev_actions->actions, actions, size);
     netdev_actions->size = size;
+    if (size) {
+        memcpy(netdev_actions->actions, actions, size);
+    }
 
     return netdev_actions;
 }

lib/ofp-actions.c

@@ -9157,7 +9157,7 @@ bool
 ofpacts_equal(const struct ofpact *a, size_t a_len,
               const struct ofpact *b, size_t b_len)
 {
-    return a_len == b_len && !memcmp(a, b, a_len);
+    return a_len == b_len && (!a_len || !memcmp(a, b, a_len));
 }
 
 /* Returns true if the 'a_len' bytes of actions in 'a' and the 'b_len' bytes of

lib/ofpbuf.c

@@ -384,6 +384,10 @@ ofpbuf_put_zeros(struct ofpbuf *b, size_t size)
 void *
 ofpbuf_put(struct ofpbuf *b, const void *p, size_t size)
 {
+    if (!size) {
+        return ofpbuf_tail(b);
+    }
+
     void *dst = ofpbuf_put_uninit(b, size);
     memcpy(dst, p, size);
     return dst;

lib/ovsdb-data.c

@@ -1967,6 +1967,10 @@ ovsdb_datum_push_unsafe(struct ovsdb_datum *dst,
                         unsigned int start_idx, unsigned int n,
                         const struct ovsdb_type *type)
 {
+    if (n == 0) {
+        return;
+    }
+
     memcpy(&dst->keys[dst->n], &src->keys[start_idx], n * sizeof src->keys[0]);
     if (type->value.type != OVSDB_TYPE_VOID) {
         memcpy(&dst->values[dst->n], &src->values[start_idx],

ofproto/ofproto-dpif-rid.c

@@ -156,7 +156,7 @@ frozen_state_equal(const struct frozen_state *a, const struct frozen_state *b)
             && uuid_equals(&a->ofproto_uuid, &b->ofproto_uuid)
             && !memcmp(&a->metadata, &b->metadata, sizeof a->metadata)
             && a->stack_size == b->stack_size
-            && !memcmp(a->stack, b->stack, a->stack_size)
+            && (!a->stack_size || !memcmp(a->stack, b->stack, a->stack_size))
             && a->mirrors == b->mirrors
             && a->conntracked == b->conntracked
             && a->was_mpls == b->was_mpls
@@ -164,7 +164,9 @@ frozen_state_equal(const struct frozen_state *a, const struct frozen_state *b)
                              b->ofpacts, b->ofpacts_len)
             && ofpacts_equal(a->action_set, a->action_set_len,
                              b->action_set, b->action_set_len)
-            && !memcmp(a->userdata, b->userdata, a->userdata_len)
+            && a->userdata_len == b->userdata_len
+            && (!a->userdata_len
+                || !memcmp(a->userdata, b->userdata, a->userdata_len))
             && uuid_equals(&a->xport_uuid, &b->xport_uuid));
 }
 

ovsdb/monitor.c

@@ -405,6 +405,10 @@ ovsdb_monitor_columns_sort(struct ovsdb_monitor *dbmon)
     SHASH_FOR_EACH (node, &dbmon->tables) {
         struct ovsdb_monitor_table *mt = node->data;
 
+        if (mt->n_columns == 0) {
+            continue;
+        }
+
         qsort(mt->columns, mt->n_columns, sizeof *mt->columns,
               compare_ovsdb_monitor_column);
         for (i = 0; i < mt->n_columns; i++) {