list: use multi-variable helpers for list loops.

Use multi-variable iteration helpers to rewrite non-safe loops.

There is an important behavior change compared with the previous
implementation: When the loop ends normally (i.e: not via "break;"), the
object pointer provided by the user is NULL. This is safer because it's
not guaranteed that it would end up pointing a valid address.

For pop iterator, set the variable to NULL when the loop ends.

Clang-analyzer has successfully picked the potential null-pointer
dereference on the code that triggered this change (bond.c) and nothing
else has been detected.

For _SAFE loops, use the LONG version for backwards compatibility.

Acked-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Dumitru Ceara <dceara@redhat.com>
Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

3 files changed, 54 insertions, 35 deletions

diff --git a/include/openvswitch/list.h b/include/openvswitch/list.h
index 8ad5eeb32..bbd2edbd0 100644
--- a/include/openvswitch/list.h
+++ b/include/openvswitch/list.h
@@ -72,37 +72,48 @@ static inline bool ovs_list_is_empty(const struct ovs_list *);
 static inline bool ovs_list_is_singleton(const struct ovs_list *);
 static inline bool ovs_list_is_short(const struct ovs_list *);
 
-#define LIST_FOR_EACH(ITER, MEMBER, LIST)                               \
-    for (INIT_CONTAINER(ITER, (LIST)->next, MEMBER);                    \
-         &(ITER)->MEMBER != (LIST);                                     \
-         ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.next, MEMBER))
-#define LIST_FOR_EACH_CONTINUE(ITER, MEMBER, LIST)                      \
-    for (ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.next, MEMBER);             \
-         &(ITER)->MEMBER != (LIST);                                     \
-         ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.next, MEMBER))
-#define LIST_FOR_EACH_REVERSE(ITER, MEMBER, LIST)                       \
-    for (INIT_CONTAINER(ITER, (LIST)->prev, MEMBER);                    \
-         &(ITER)->MEMBER != (LIST);                                     \
-         ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER))
-#define LIST_FOR_EACH_REVERSE_SAFE(ITER, PREV, MEMBER, LIST)        \
-    for (INIT_CONTAINER(ITER, (LIST)->prev, MEMBER);                \
-         (&(ITER)->MEMBER != (LIST)                                 \
-          ? INIT_CONTAINER(PREV, (ITER)->MEMBER.prev, MEMBER), 1    \
-          : 0);                                                     \
-         (ITER) = (PREV))
-#define LIST_FOR_EACH_REVERSE_CONTINUE(ITER, MEMBER, LIST)              \
-    for (ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER);           \
-         &(ITER)->MEMBER != (LIST);                                     \
-         ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER))
-#define LIST_FOR_EACH_SAFE(ITER, NEXT, MEMBER, LIST)               \
-    for (INIT_CONTAINER(ITER, (LIST)->next, MEMBER);               \
-         (&(ITER)->MEMBER != (LIST)                                \
-          ? INIT_CONTAINER(NEXT, (ITER)->MEMBER.next, MEMBER), 1   \
-          : 0);                                                    \
-         (ITER) = (NEXT))
-#define LIST_FOR_EACH_POP(ITER, MEMBER, LIST)                      \
-    while (!ovs_list_is_empty(LIST)                                    \
-           && (INIT_CONTAINER(ITER, ovs_list_pop_front(LIST), MEMBER), 1))
+#define LIST_FOR_EACH(VAR, MEMBER, LIST)                                      \
+    for (INIT_MULTIVAR(VAR, MEMBER, (LIST)->next, struct ovs_list);           \
+         CONDITION_MULTIVAR(VAR, MEMBER, ITER_VAR(VAR) != (LIST));            \
+         UPDATE_MULTIVAR(VAR, ITER_VAR(VAR)->next))
+
+#define LIST_FOR_EACH_CONTINUE(VAR, MEMBER, LIST)                             \
+    for (INIT_MULTIVAR(VAR, MEMBER, VAR->MEMBER.next, struct ovs_list);       \
+         CONDITION_MULTIVAR(VAR, MEMBER, ITER_VAR(VAR) != (LIST));            \
+         UPDATE_MULTIVAR(VAR, ITER_VAR(VAR)->next))
+
+#define LIST_FOR_EACH_REVERSE(VAR, MEMBER, LIST)                              \
+    for (INIT_MULTIVAR(VAR, MEMBER, (LIST)->prev, struct ovs_list);           \
+         CONDITION_MULTIVAR(VAR, MEMBER, ITER_VAR(VAR) != (LIST));            \
+         UPDATE_MULTIVAR(VAR, ITER_VAR(VAR)->prev))
+
+#define LIST_FOR_EACH_REVERSE_CONTINUE(VAR, MEMBER, LIST)                     \
+    for (INIT_MULTIVAR(VAR, MEMBER, VAR->MEMBER.prev, struct ovs_list);       \
+         CONDITION_MULTIVAR(VAR, MEMBER, ITER_VAR(VAR) != (LIST));            \
+         UPDATE_MULTIVAR(VAR, ITER_VAR(VAR)->prev))
+
+#define LIST_FOR_EACH_REVERSE_SAFE(VAR, PREV, MEMBER, LIST)                   \
+    for (INIT_MULTIVAR_SAFE_LONG(VAR, PREV, MEMBER, (LIST)->prev,             \
+                                 struct ovs_list);                            \
+         CONDITION_MULTIVAR_SAFE_LONG(VAR, PREV, MEMBER,                      \
+                                      ITER_VAR(VAR) != (LIST),                \
+                                      ITER_VAR(PREV) = ITER_VAR(VAR)->prev,   \
+                                      ITER_VAR(PREV) != (LIST));              \
+         UPDATE_MULTIVAR_SAFE_LONG(VAR, PREV))
+
+#define LIST_FOR_EACH_SAFE(VAR, NEXT, MEMBER, LIST)                           \
+    for (INIT_MULTIVAR_SAFE_LONG(VAR, NEXT, MEMBER, (LIST)->next,             \
+                                 struct ovs_list);                            \
+         CONDITION_MULTIVAR_SAFE_LONG(VAR, NEXT, MEMBER,                      \
+                                      ITER_VAR(VAR) != (LIST),                \
+                                      ITER_VAR(NEXT) = ITER_VAR(VAR)->next,   \
+                                      ITER_VAR(NEXT) != (LIST));              \
+         UPDATE_MULTIVAR_SAFE_LONG(VAR, NEXT))
+
+#define LIST_FOR_EACH_POP(ITER, MEMBER, LIST)                                 \
+    while (!ovs_list_is_empty(LIST) ?                                         \
+           (INIT_CONTAINER(ITER, ovs_list_pop_front(LIST), MEMBER), 1) :      \
+           (ITER = NULL, 0))
 
 /* Inline implementations. */
 
diff --git a/ofproto/bond.c b/ofproto/bond.c
index 405202fb6..54e06211a 100644
--- a/ofproto/bond.c
+++ b/ofproto/bond.c
@@ -1165,7 +1165,7 @@ insert_bal(struct ovs_list *bals, struct bond_slave *slave)
             break;
         }
     }
-    ovs_list_insert(&pos->bal_node, &slave->bal_node);
+    ovs_list_insert(pos ? &pos->bal_node : bals, &slave->bal_node);
 }
 
 /* Removes 'slave' from its current list and then inserts it into 'bals' so
diff --git a/tests/test-list.c b/tests/test-list.c
index 6f1fb059b..648e02a5e 100644
--- a/tests/test-list.c
+++ b/tests/test-list.c
@@ -61,7 +61,7 @@ check_list(struct ovs_list *list, const int values[], size_t n)
         assert(e->value == values[i]);
         i++;
     }
-    assert(&e->node == list);
+    assert(e == NULL);
     assert(i == n);
 
     i = 0;
@@ -70,7 +70,7 @@ check_list(struct ovs_list *list, const int values[], size_t n)
         assert(e->value == values[n - i - 1]);
         i++;
     }
-    assert(&e->node == list);
+    assert(e == NULL);
     assert(i == n);
 
     assert(ovs_list_is_empty(list) == !n);
@@ -135,6 +135,13 @@ test_list_for_each_safe(void)
             values_idx = 0;
             n_remaining = n;
             LIST_FOR_EACH_SAFE (e, next, node, &list) {
+                /* "next" is valid as long as it's not pointing to &list. */
+                if (&e->node == list.prev) {
+                    assert(next == NULL);
+                } else {
+                    assert(&next->node == e->node.next);
+                }
+
                 assert(i < n);
                 if (pattern & (1ul << i)) {
                     ovs_list_remove(&e->node);
@@ -148,7 +155,8 @@ test_list_for_each_safe(void)
                 i++;
             }
             assert(i == n);
-            assert(&e->node == &list);
+            assert(e == NULL);
+            assert(next == NULL);
 
             for (i = 0; i < n; i++) {
                 if (pattern & (1ul << i)) {