desktop-file: Treat backslashes in section names as literal

The Desktop Entry Specification doesn't give any special meaning to
backslashes in section names: a line "[\n]" starts a section whose
name is the two characters (backslash, n), not a section whose name
is a newline. GKeyFile in GLib matches this interpretation.

In practice, the only section used by dbus-daemon is "D-BUS Service",
only way this could make a difference is if someone had written it
as "D-BUS\sService". According to
https://codesearch.debian.net/search?q=%5C%5BD-BUS%5C%5CsService%5C%5D
there is no instance of that pattern in Debian.

Signed-off-by: Simon McVittie <smcv@collabora.com>

bus/desktop-file.c

@@ -302,7 +302,7 @@ new_section (BusDesktopFile *desktop_file,
 
 static BusDesktopFileSection* 
 open_section (BusDesktopFileParser *parser,
-              char                 *name)
+              const char           *name)
 {  
   BusDesktopFileSection *section;
 
@@ -376,8 +376,15 @@ parse_comment_or_blank (BusDesktopFileParser *parser)
 }
 
 static dbus_bool_t
-is_valid_section_name (const char *name)
+is_valid_section_name (const DBusString *section_name)
 {
+  int i;
+  int len;
+  const unsigned char *data;
+
+  len = _dbus_string_get_length (section_name);
+  data = _dbus_string_get_const_udata_len (section_name, 0, len);
+
   /* 5. Group names may contain all ASCII characters except for control characters and '[' and ']'.
    *
    * We don't use isprint() here because it's locale-dependent. ASCII
@@ -385,12 +392,12 @@ is_valid_section_name (const char *name)
    * values >= 0x80 aren't ASCII. 0x20 is a space, which we must allow,
    * not least because DBUS_SERVICE_SECTION contains one. */
 
-  while (*name)
+  for (i = 0; i < len; i++)
     {
-      if (*name <= 0x1f || *name >= 0x7f || *name  == '[' || *name == ']')
+      unsigned char c = data[i];
+
+      if (c <= 0x1f || c >= 0x7f || c  == '[' || c == ']')
 	return FALSE;
-      
-      name++;
     }
 
   return TRUE;
@@ -400,7 +407,7 @@ static dbus_bool_t
 parse_section_start (BusDesktopFileParser *parser, DBusError *error)
 {
   int line_end, eol_len;
-  char *section_name;
+  DBusString section_name;
 
   _DBUS_ASSERT_ERROR_IS_CLEAR (error);
     
@@ -415,27 +422,34 @@ parse_section_start (BusDesktopFileParser *parser, DBusError *error)
       return FALSE;
     }
 
-  section_name = unescape_string (parser,
-                                  &parser->data, parser->pos + 1, line_end - 1,
-                                  error);
-
-  if (section_name == NULL)
+  if (!_dbus_string_init (&section_name))
     {
       parser_free (parser);
+      BUS_SET_OOM (error);
       return FALSE;
     }
 
-  if (!is_valid_section_name (section_name))
+  if (!_dbus_string_copy_len (&parser->data, parser->pos + 1,
+                              line_end - parser->pos - 2,
+                              &section_name, 0))
+    {
+      parser_free (parser);
+      _dbus_string_free (&section_name);
+      BUS_SET_OOM (error);
+      return FALSE;
+    }
+
+  if (!is_valid_section_name (&section_name))
     {
       report_error (parser, "Invalid characters in section name", BUS_DESKTOP_PARSE_ERROR_INVALID_CHARS, error);
       parser_free (parser);
-      dbus_free (section_name);
+      _dbus_string_free (&section_name);
       return FALSE;
     }
 
-  if (open_section (parser, section_name) == NULL)
+  if (open_section (parser, _dbus_string_get_const_data (&section_name)) == NULL)
     {
-      dbus_free (section_name);
+      _dbus_string_free (&section_name);
       parser_free (parser);
       BUS_SET_OOM (error);
       return FALSE;
@@ -448,7 +462,7 @@ parse_section_start (BusDesktopFileParser *parser, DBusError *error)
   
   parser->line_num += 1;
 
-  dbus_free (section_name);
+  _dbus_string_free (&section_name);
   
   return TRUE;
 }

test/internals/desktop-file.c

@@ -86,13 +86,19 @@ static const Test valid_content[] =
   { "odd whitespace",
     "\n\n    \n[D-BUS Service]\n    \n",
     -1 },
-  /* Note that backslash is not included here. dbus-daemon currently
-   * interprets group names in the same way as string values, with
-   * backslash escapes interpreted; this does not appear to match
-   * the Desktop Entry Specification or the implementation in GKeyFile. */
   { "Misc printable ASCII in section heading",
-    "[abcxyzABCXYZ012789`!\"$%^&*()-_=+{}:;'@#~<,>./?|]",
+    "[abcxyzABCXYZ012789`!\"$%^&*()-_=+{}:;'@#~<,>./?|\\]",
     -1 },
+  { "Backslash in section heading",
+    /* Section name consists of a single backslash followed by literal n
+     * (it is not a newline) */
+    "[\\n]\n"
+    "foo=bar",
+    -1,
+    "\\n",
+    "foo",
+    "bar",
+    "bar" },
   { "empty", "", -1 }
 };