Patch some memory leaks.

capture_dev_user_descr_find() and capture_dev_user_cfilter_find() return
g_malloc()ated strings; we don't need to g_strdup() them to get a
g_malloc()ated string, and we *do* need to free them if we aren't going
to use them any more.

Document that while we're at it, and give more details for the functions
returning integer user-specified interface parameters as well.

Change-Id: Icf98a48992b1c4168ead54bdc4cc2847da89d665
Reviewed-on: https://code.wireshark.org/review/7745
Reviewed-by: Guy Harris <guy@alum.mit.edu>

4 files changed, 73 insertions, 45 deletions

diff --git a/ui/capture_ui_utils.c b/ui/capture_ui_utils.c
index 4bac875056..50317f1431 100644
--- a/ui/capture_ui_utils.c
+++ b/ui/capture_ui_utils.c
@@ -276,52 +276,52 @@ get_interface_descriptive_name(const char *if_name)
 
   /* Do we have a user-supplied description? */
   descr = capture_dev_user_descr_find(if_name);
-  if (descr != NULL) {
-    /* Yes - make a copy of that. */
-    descr = g_strdup(descr);
-  } else if (strcmp(if_name, "-") == 0) {
-    /*
-     * Strictly speaking, -X (extension) options are for modules, e.g. Lua
-     * and using one here stretches that definition. However, this doesn't
-     * waste a single-letter option on something that might be rarely used
-     * and is backward-compatible to 1.0.
-     */
-    descr = g_strdup(ex_opt_get_nth("stdin_descr", 0));
-    if (!descr) {
-      descr = g_strdup("Standard input");
-    }
-  } else {
-    /* No, we don't have a user-supplied description; did we get
-       one from the OS or libpcap? */
-    descr = NULL;
-    if_list = capture_interface_list(&err, NULL, NULL);
-    if (if_list != NULL) {
-      if_entry = if_list;
-      do {
-        if_info = (if_info_t *)if_entry->data;
-        if (strcmp(if_info->name, if_name) == 0) {
-          if (if_info->friendly_name != NULL) {
-              /* We have a "friendly name"; return a copy of that
-                 as the description - when we free the interface
-                 list, that'll also free up the strings to which
-                 it refers. */
-              descr = g_strdup(if_info->friendly_name);
-          } else if (if_info->vendor_description != NULL) {
-            /* We have no "friendly name", but we have a vendor
-               description; return a copy of that - when we free
-               the interface list, that'll also free up the strings
-               to which it refers. */
-            descr = g_strdup(if_info->vendor_description);
+  if (descr == NULL) {
+    /* No; try to construct a descriptive name. */
+    if (strcmp(if_name, "-") == 0) {
+      /*
+       * Strictly speaking, -X (extension) options are for modules, e.g. Lua
+       * and using one here stretches that definition. However, this doesn't
+       * waste a single-letter option on something that might be rarely used
+       * and is backward-compatible to 1.0.
+       */
+      descr = g_strdup(ex_opt_get_nth("stdin_descr", 0));
+      if (!descr) {
+        descr = g_strdup("Standard input");
+      }
+    } else {
+      /* No, we don't have a user-supplied description; did we get
+         one from the OS or libpcap? */
+      descr = NULL;
+      if_list = capture_interface_list(&err, NULL, NULL);
+      if (if_list != NULL) {
+        if_entry = if_list;
+        do {
+          if_info = (if_info_t *)if_entry->data;
+          if (strcmp(if_info->name, if_name) == 0) {
+            if (if_info->friendly_name != NULL) {
+                /* We have a "friendly name"; return a copy of that
+                   as the description - when we free the interface
+                   list, that'll also free up the strings to which
+                   it refers. */
+                descr = g_strdup(if_info->friendly_name);
+            } else if (if_info->vendor_description != NULL) {
+              /* We have no "friendly name", but we have a vendor
+                 description; return a copy of that - when we free
+                 the interface list, that'll also free up the strings
+                 to which it refers. */
+              descr = g_strdup(if_info->vendor_description);
+            }
+            break;
           }
-          break;
-        }
-      } while ((if_entry = g_list_next(if_entry)) != NULL);
-    }
-    free_interface_list(if_list);
+        } while ((if_entry = g_list_next(if_entry)) != NULL);
+      }
+      free_interface_list(if_list);
 
-    if (descr == NULL) {
-      /* The interface name is all we have, so just return a copy of that. */
-      descr = g_strdup(if_name);
+      if (descr == NULL) {
+        /* The interface name is all we have, so just return a copy of that. */
+        descr = g_strdup(if_name);
+      }
     }
   }
 
diff --git a/ui/capture_ui_utils.h b/ui/capture_ui_utils.h
index 28c117f02a..6b5361f83e 100644
--- a/ui/capture_ui_utils.h
+++ b/ui/capture_ui_utils.h
@@ -36,12 +36,21 @@ extern "C" {
 /**
  * Find user-specified capture device description that matches interface
  * name, if any.
+ *
+ * @param if_name The name of the interface.
+ *
+ * @return The device description (must be g_free'd later) or NULL
+ * if not found.
  */
 char *capture_dev_user_descr_find(const gchar *if_name);
 
 /**
  * Find user-specified link-layer header type that matches interface
  * name, if any.
+ *
+ * @param if_name The name of the interface.
+ *
+ * @return The link-layer header type (a DLT_) or -1 if not found.
  */
 gint capture_dev_user_linktype_find(const gchar *if_name);
 
@@ -49,6 +58,10 @@ gint capture_dev_user_linktype_find(const gchar *if_name);
 /**
  * Find user-specified buffer size that matches interface
  * name, if any.
+ *
+ * @param if_name The name of the interface.
+ *
+ * @return The buffer size or -1 if not found.
  */
 gint capture_dev_user_buffersize_find(const gchar *if_name);
 #endif
@@ -56,6 +69,16 @@ gint capture_dev_user_buffersize_find(const gchar *if_name);
 /**
  * Find user-specified snap length that matches interface
  * name, if any.
+ *
+ * @param if_name The name of the interface.
+ * @param hassnap Pointer to a variable to be set to TRUE if the
+ * interface should be given a snap length or FALSE if it shouldn't
+ * be given a snap length.
+ * @param snaplen Pointer to a variable to be set to the snap length
+ * if the interface should be given a snap length or the maximum
+ * snap length if it shouldn't be given a snap length.
+ *
+ * @return TRUE if found or FALSE if not found.
  */
 gboolean capture_dev_user_snaplen_find(const gchar *if_name, gboolean *hassnap, int *snaplen);
 
@@ -68,6 +91,10 @@ gboolean capture_dev_user_pmode_find(const gchar *if_name);
 /**
  * Find user-specified capture filter that matches interface
  * name, if any.
+ *
+ * @param if_name The name of the interface.
+ *
+ * @return The capture filter (must be g_free'd later) or NULL if not found.
  */
 gchar* capture_dev_user_cfilter_find(const gchar *if_name);
 
diff --git a/ui/qt/capture_interfaces_dialog.cpp b/ui/qt/capture_interfaces_dialog.cpp
index 89aceee1e3..f1c8539429 100644
--- a/ui/qt/capture_interfaces_dialog.cpp
+++ b/ui/qt/capture_interfaces_dialog.cpp
@@ -537,7 +537,7 @@ void CaptureInterfacesDialog::updateInterfaces()
 #endif
             gchar* prefFilter = capture_dev_user_cfilter_find(device->name);
             if (prefFilter) {
-                device->cfilter = g_strdup(prefFilter);
+                device->cfilter = prefFilter;
             }
             ti->setText(col_filter_, device->cfilter);
 
diff --git a/ui/qt/manage_interfaces_dialog.cpp b/ui/qt/manage_interfaces_dialog.cpp
index 93164c5fa8..4b36fa1256 100644
--- a/ui/qt/manage_interfaces_dialog.cpp
+++ b/ui/qt/manage_interfaces_dialog.cpp
@@ -334,6 +334,7 @@ void ManageInterfacesDialog::showLocalInterfaces()
             comment = capture_dev_user_descr_find(device.name);
             if (comment) {
                 item->setText(col_l_comment_, comment);
+                g_free(comment);
             }
         } else {
           continue;