fix: memory leak during conference load

This was found in our continous fuzzing setup.

toxcore/group.c

@@ -3392,19 +3392,21 @@ uint8_t *conferences_save(const Group_Chats *g_c, uint8_t *data)
     return data;
 }
 
+/**
+ * @brief load_group Load a Group section from a save file
+ * @param g Group to load
+ * @param g_c Reference to all groupchats, need for utility functions
+ * @param data Start of the data to deserialze
+ * @param length Length of data
+ * @return 0 on error, number of consumed bytes otherwise
+ */
 non_null()
-static State_Load_Status load_conferences(Group_Chats *g_c, const uint8_t *data, uint32_t length)
+static uint32_t load_group(Group_c *g, const Group_Chats *g_c, const uint8_t *data, uint32_t length)
 {
     const uint8_t *init_data = data;
 
-    while (length >= (uint32_t)(data - init_data) + SAVED_CONF_SIZE_CONSTANT) {
-        const int groupnumber = create_group_chat(g_c);
-
-        if (groupnumber == -1) {
-            return STATE_LOAD_STATUS_ERROR;
-        }
-
-        Group_c *g = &g_c->chats[groupnumber];
+    // Initialize to default values so we can unconditionally free in case of an error
+    setup_conference(g);
 
     g->type = *data;
     ++data;
@@ -3428,28 +3430,34 @@ static State_Load_Status load_conferences(Group_Chats *g_c, const uint8_t *data,
         g->frozen = (Group_Peer *)calloc(g->numfrozen, sizeof(Group_Peer));
 
         if (g->frozen == nullptr) {
-                return STATE_LOAD_STATUS_ERROR;
+            // Memory allocation failure
+            return 0;
         }
     }
 
     g->title_len = *data;
 
     if (g->title_len > MAX_NAME_LENGTH) {
-            return STATE_LOAD_STATUS_ERROR;
+        return 0;
     }
 
     ++data;
 
+    assert((data - init_data) < UINT32_MAX);
+
     if (length < (uint32_t)(data - init_data) + g->title_len) {
-            return STATE_LOAD_STATUS_ERROR;
+        return 0;
     }
 
     memcpy(g->title, data, g->title_len);
     data += g->title_len;
 
     for (uint32_t j = 0; j < g->numfrozen; ++j) {
+
+        assert((data - init_data) < UINT32_MAX);
+
         if (length < (uint32_t)(data - init_data) + SAVED_PEER_SIZE_CONSTANT) {
-                return STATE_LOAD_STATUS_ERROR;
+            return 0;
         }
 
         Group_Peer *peer = &g->frozen[j];
@@ -3469,13 +3477,14 @@ static State_Load_Status load_conferences(Group_Chats *g_c, const uint8_t *data,
         peer->nick_len = *data;
 
         if (peer->nick_len > MAX_NAME_LENGTH) {
-                return STATE_LOAD_STATUS_ERROR;
+            return 0;
         }
 
         ++data;
+        assert((data - init_data) < UINT32_MAX);
 
         if (length < (uint32_t)(data - init_data) + peer->nick_len) {
-                return STATE_LOAD_STATUS_ERROR;
+            return 0;
         }
 
         memcpy(peer->nick, data, peer->nick_len);
@@ -3490,7 +3499,49 @@ static State_Load_Status load_conferences(Group_Chats *g_c, const uint8_t *data,
     }
 
     g->status = GROUPCHAT_STATUS_CONNECTED;
-        memcpy(g->real_pk, nc_get_self_public_key(g_c->m->net_crypto), CRYPTO_PUBLIC_KEY_SIZE);
+
+    id_copy(g->real_pk, nc_get_self_public_key(g_c->m->net_crypto));
+
+    assert((data - init_data) < UINT32_MAX);
+
+    return (uint32_t)(data - init_data);
+}
+
+non_null()
+static State_Load_Status load_conferences_helper(Group_Chats *g_c, const uint8_t *data, uint32_t length)
+{
+    const uint8_t *init_data = data;
+
+    while (length >= (uint32_t)(data - init_data) + SAVED_CONF_SIZE_CONSTANT) {
+        const int groupnumber = create_group_chat(g_c);
+
+        // Helpful for testing
+        assert(groupnumber != -1);
+
+        if (groupnumber == -1) {
+            // If this fails there's a serious problem, don't bother with cleanup
+            return STATE_LOAD_STATUS_ERROR;
+        }
+
+        Group_c *g = &g_c->chats[groupnumber];
+
+        const uint32_t consumed = load_group(g, g_c, data, length - (uint32_t)(data - init_data));
+
+        if (consumed == 0) {
+            // remove partially loaded stuff, wipe_group_chat must be able to wipe a partially loaded group
+            const bool ret = wipe_group_chat(g_c, groupnumber);
+
+            // HACK: suppress unused variable warning
+            if (!ret) {
+                // wipe_group_chat(...) must be able to wipe partially allocated groups
+                assert(ret == true);
+            }
+
+            return STATE_LOAD_STATUS_ERROR;
+        }
+
+        data += consumed;
+
         const int peer_index = addpeer(g_c, groupnumber, g->real_pk, dht_get_self_public_key(g_c->m->dht), g->peer_number,
                                        nullptr, true, false);
 
@@ -3504,6 +3555,27 @@ static State_Load_Status load_conferences(Group_Chats *g_c, const uint8_t *data,
     return STATE_LOAD_STATUS_CONTINUE;
 }
 
+non_null()
+static State_Load_Status load_conferences(Group_Chats *g_c, const uint8_t *data, uint32_t length)
+{
+    const State_Load_Status res = load_conferences_helper(g_c, data, length);
+
+    if (res == STATE_LOAD_STATUS_CONTINUE) {
+        return res;
+    }
+
+    // Loading failed, cleanup all Group_c
+
+    // save locally, because wipe_group_chat(...) modifies it
+    const uint16_t num_groups = g_c->num_chats;
+
+    for (uint16_t i = 0; i < num_groups; ++i) {
+        wipe_group_chat(g_c, i);
+    }
+
+    return res;
+}
+
 bool conferences_load_state_section(Group_Chats *g_c, const uint8_t *data, uint32_t length, uint16_t type,
                                     State_Load_Status *status)
 {