Fix a few crashes and leaks when cloning C strings.

* alloc.c, lisp.h (dupstring): New function.
* gtkutil.c (xg_get_font):
* term.c (tty_default_color_capabilities):
* xsettings.c (store_monospaced_changed)
(store_font_name_changed, parse_settings)
(read_and_apply_settings, init_gsettings, init_gconf): Use it.
This avoids some unlikely crashes due to accessing freed storage,
and avoids some minor memory leaks in the more-typical case.

6 files changed, 40 insertions, 27 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index d2eeab33e4f..704ac68b67e 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,15 @@
+2014-02-28  Paul Eggert  <eggert@penguin.cs.ucla.edu>
+
+        Fix a few crashes and leaks when cloning C strings.
+        * alloc.c, lisp.h (dupstring): New function.
+        * gtkutil.c (xg_get_font):
+        * term.c (tty_default_color_capabilities):
+        * xsettings.c (store_monospaced_changed)
+        (store_font_name_changed, parse_settings)
+        (read_and_apply_settings, init_gsettings, init_gconf): Use it.
+        This avoids some unlikely crashes due to accessing freed storage,
+        and avoids some minor memory leaks in the more-typical case.
+
 2014-02-28  Martin Rudalics  <rudalics@gmx.at>
 
         * xdisp.c (note_mode_line_or_margin_highlight): Don't show drag
diff --git a/src/alloc.c b/src/alloc.c
index 7f0a74ca834..7c671e25cfc 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -850,6 +850,20 @@ xlispstrdup (Lisp_Object string)
   return memcpy (xmalloc (size), SSDATA (string), size);
 }
 
+/* Assign to *PTR a copy of STRING, freeing any storage *PTR formerly
+   pointed to.  If STRING is null, assign it without copying anything.
+   Allocate before freeing, to avoid a dangling pointer if allocation
+   fails.  */
+
+void
+dupstring (char **ptr, char const *string)
+{
+  char *old = *ptr;
+  *ptr = string ? xstrdup (string) : 0;
+  xfree (old);
+}
+
+
 /* Like putenv, but (1) use the equivalent of xmalloc and (2) the
    argument is a const pointer.  */
 
diff --git a/src/gtkutil.c b/src/gtkutil.c
index 6e039c7a141..cebff68614f 100644
--- a/src/gtkutil.c
+++ b/src/gtkutil.c
@@ -2106,8 +2106,7 @@ xg_get_font (struct frame *f, const char *default_name)
           font = Ffont_spec (8, args);
 
           pango_font_description_free (desc);
-          xfree (x_last_font_name);
-          x_last_font_name = xstrdup (name);
+          dupstring (&x_last_font_name, name);
         }
 
 #else /* Use old font selector, which just returns the font name.  */
diff --git a/src/lisp.h b/src/lisp.h
index a7e80a41c28..2f9a30fdfe9 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4398,6 +4398,7 @@ extern void *xpalloc (void *, ptrdiff_t *, ptrdiff_t, ptrdiff_t, ptrdiff_t);
 
 extern char *xstrdup (const char *);
 extern char *xlispstrdup (Lisp_Object);
+extern void dupstring (char **, char const *);
 extern void xputenv (const char *);
 
 extern char *egetenv (const char *);
diff --git a/src/term.c b/src/term.c
index 0c40c2d16b9..61a8d39d971 100644
--- a/src/term.c
+++ b/src/term.c
@@ -2052,17 +2052,9 @@ tty_default_color_capabilities (struct tty_display_info *tty, bool save)
 
   if (save)
     {
-      xfree (default_orig_pair);
-      default_orig_pair = tty->TS_orig_pair ? xstrdup (tty->TS_orig_pair) : NULL;
-
-      xfree (default_set_foreground);
-      default_set_foreground = tty->TS_set_foreground ? xstrdup (tty->TS_set_foreground)
-                               : NULL;
-
-      xfree (default_set_background);
-      default_set_background = tty->TS_set_background ? xstrdup (tty->TS_set_background)
-                               : NULL;
-
+      dupstring (&default_orig_pair, tty->TS_orig_pair);
+      dupstring (&default_set_foreground, tty->TS_set_foreground);
+      dupstring (&default_set_background, tty->TS_set_background);
       default_max_colors = tty->TN_max_colors;
       default_max_pairs = tty->TN_max_pairs;
       default_no_color_video = tty->TN_no_color_video;
diff --git a/src/xsettings.c b/src/xsettings.c
index 458c3d45e9a..844da19f638 100644
--- a/src/xsettings.c
+++ b/src/xsettings.c
@@ -91,8 +91,7 @@ store_monospaced_changed (const char *newfont)
   if (current_mono_font != NULL && strcmp (newfont, current_mono_font) == 0)
     return; /* No change. */
 
-  xfree (current_mono_font);
-  current_mono_font = xstrdup (newfont);
+  dupstring (&current_mono_font, newfont);
 
   if (dpyinfo_valid (first_dpyinfo) && use_system_font)
     {
@@ -111,8 +110,7 @@ store_font_name_changed (const char *newfont)
   if (current_font != NULL && strcmp (newfont, current_font) == 0)
     return; /* No change. */
 
-  xfree (current_font);
-  current_font = xstrdup (newfont);
+  dupstring (&current_font, newfont);
 
   if (dpyinfo_valid (first_dpyinfo))
     {
@@ -492,13 +490,13 @@ parse_settings (unsigned char *prop,
           ++settings_seen;
           if (strcmp (name, XSETTINGS_TOOL_BAR_STYLE) == 0)
             {
-              settings->tb_style = xstrdup (sval);
+              dupstring (&settings->tb_style, sval);
               settings->seen |= SEEN_TB_STYLE;
             }
 #ifdef HAVE_XFT
           else if (strcmp (name, XSETTINGS_FONT_NAME) == 0)
             {
-              settings->font = xstrdup (sval);
+              dupstring (&settings->font, sval);
               settings->seen |= SEEN_FONT;
             }
           else if (strcmp (name, "Xft/Antialias") == 0)
@@ -742,10 +740,7 @@ read_and_apply_settings (struct x_display_info *dpyinfo, int send_event_p)
       if (send_event_p)
         store_font_name_changed (settings.font);
       else
-        {
-          xfree (current_font);
-          current_font = xstrdup (settings.font);
-        }
+        dupstring (&current_font, settings.font);
       xfree (settings.font);
     }
 #endif
@@ -835,7 +830,7 @@ init_gsettings (void)
     {
       g_variant_ref_sink (val);
       if (g_variant_is_of_type (val, G_VARIANT_TYPE_STRING))
-        current_mono_font = xstrdup (g_variant_get_string (val, NULL));
+        dupstring (&current_mono_font, g_variant_get_string (val, NULL));
       g_variant_unref (val);
     }
 
@@ -844,7 +839,7 @@ init_gsettings (void)
     {
       g_variant_ref_sink (val);
       if (g_variant_is_of_type (val, G_VARIANT_TYPE_STRING))
-        current_font = xstrdup (g_variant_get_string (val, NULL));
+        dupstring (&current_font, g_variant_get_string (val, NULL));
       g_variant_unref (val);
     }
 #endif /* HAVE_XFT */
@@ -886,13 +881,13 @@ init_gconf (void)
   s = gconf_client_get_string (gconf_client, GCONF_MONO_FONT, NULL);
   if (s)
     {
-      current_mono_font = xstrdup (s);
+      dupstring (&current_mono_font, s);
       g_free (s);
     }
   s = gconf_client_get_string (gconf_client, GCONF_FONT_NAME, NULL);
   if (s)
     {
-      current_font = xstrdup (s);
+      dupstring (&current_font, s);
       g_free (s);
     }
   gconf_client_add_dir (gconf_client,