BUG#58246: INSTALL PLUGIN not secure & crashable

When installing plugins, there is a missing check
for slash (/) in the path on Windows. Note that on
Windows, both / and \ can be used to separate
directories.

This patch fixes the issue by:
- Adding a FN_DIRSEP symbol for all platforms
  consisting of a string of legal directory
  separators.
- Adding a charset-aware version of strcspn().
- Adding a check_valid_path() function that uses
  my_strcspn() to check if any FN_DIRSEP character
  is in the supplied string.
- Using the check_valid_path() function in
  sql_plugin.cc and sql_udf.cc (which means
  replacing the existing test there).

include/config-netware.h:
  Adding FN_DIRSEP
  ******
  Adding FN_DIRSEP
include/config-win.h:
  Adding FN_DIRSEP
  ******
  Adding FN_DIRSEP
include/m_ctype.h:
  Adding my_strspn() and my_strcspn().
  
  ******
  Adding my_strspn() and my_strcspn().
include/my_global.h:
  Adding FN_DIRSEP
  ******
  Adding FN_DIRSEP
mysql-test/t/plugin_not_embedded.test:
  Adding test that file names containing / is
  disallowed on *all* platforms.
  ******
  Adding test that file names containing / is
  disallowed on *all* platforms.
sql/sql_plugin.cc:
  Introducing check_if_path() function for
  checking if filename is a path to include
  / on Windows.
  ******
  Introducing check_if_path() function for
  checking if filename is a path to include
  / on Windows.
sql/sql_udf.cc:
  Switching to use check_if_path() function.
  ******
  Switching to use check_if_path() function.
strings/my_strchr.c:
  Adding my_strspn() and my_strcspn().
  ******
  Adding my_strspn() and my_strcspn().

3 files changed, 25 insertions, 11 deletions

diff --git a/sql/sql_plugin.cc b/sql/sql_plugin.cc
index e0fc88c3068..d8423fd153b 100644
--- a/sql/sql_plugin.cc
+++ b/sql/sql_plugin.cc
@@ -231,6 +231,26 @@ extern bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool *exists);
 #endif /* EMBEDDED_LIBRARY */
 
 
+/**
+   Check if the provided path is valid in the sense that it does cause
+   a relative reference outside the directory.
+
+   @note Currently, this function only check if there are any
+   characters in FN_DIRSEP in the string, but it might change in the
+   future.
+
+   @code
+   check_valid_path("../foo.so") -> true
+   check_valid_path("foo.so") -> false
+   @endcode
+ */
+bool check_valid_path(const char *path, size_t len)
+{
+  size_t prefix= my_strcspn(files_charset_info, path, path + len, FN_DIRSEP);
+  return  prefix < len;
+}
+
+
 /****************************************************************************
   Value type thunks, allows the C world to play in the C++ world
 ****************************************************************************/
@@ -354,13 +374,14 @@ static st_plugin_dl *plugin_dl_add(const LEX_STRING *dl, int report)
   struct st_plugin_dl *tmp, plugin_dl;
   void *sym;
   DBUG_ENTER("plugin_dl_add");
+  DBUG_PRINT("enter", ("dl->str: '%s', dl->length: %d", dl->str, dl->length));
   plugin_dir_len= strlen(opt_plugin_dir);
   /*
     Ensure that the dll doesn't have a path.
     This is done to ensure that only approved libraries from the
     plugin directory are used (to make this even remotely secure).
   */
-  if (my_strchr(files_charset_info, dl->str, dl->str + dl->length, FN_LIBCHAR) ||
+  if (check_valid_path(dl->str, dl->length) ||
       check_string_char_length((LEX_STRING *) dl, "", NAME_CHAR_LEN,
                                system_charset_info, 1) ||
       plugin_dir_len + dl->length + 1 >= FN_REFLEN)
diff --git a/sql/sql_plugin.h b/sql/sql_plugin.h
index 004d0d5abb7..72984865807 100644
--- a/sql/sql_plugin.h
+++ b/sql/sql_plugin.h
@@ -131,6 +131,7 @@ extern bool mysql_uninstall_plugin(THD *thd, const LEX_STRING *name);
 extern bool plugin_register_builtin(struct st_mysql_plugin *plugin);
 extern void plugin_thdvar_init(THD *thd);
 extern void plugin_thdvar_cleanup(THD *thd);
+extern bool check_valid_path(const char *path, size_t length);
 
 typedef my_bool (plugin_foreach_func)(THD *thd,
                                       plugin_ref plugin,
diff --git a/sql/sql_udf.cc b/sql/sql_udf.cc
index d455a66c4f2..1d5335f0652 100644
--- a/sql/sql_udf.cc
+++ b/sql/sql_udf.cc
@@ -173,10 +173,7 @@ void udf_init()
 
       On windows we must check both FN_LIBCHAR and '/'.
     */
-    if (my_strchr(files_charset_info, dl_name,
-                  dl_name + strlen(dl_name), FN_LIBCHAR) ||
-        IF_WIN(my_strchr(files_charset_info, dl_name,
-                         dl_name + strlen(dl_name), '/'), 0) ||
+    if (check_valid_path(dl_name, strlen(dl_name)) ||
         check_string_char_length(&name, "", NAME_CHAR_LEN,
                                  system_charset_info, 1))
     {
@@ -416,13 +413,8 @@ int mysql_create_function(THD *thd,udf_func *udf)
     Ensure that the .dll doesn't have a path
     This is done to ensure that only approved dll from the system
     directories are used (to make this even remotely secure).
-
-    On windows we must check both FN_LIBCHAR and '/'.
   */
-  if (my_strchr(files_charset_info, udf->dl,
-                udf->dl + strlen(udf->dl), FN_LIBCHAR) ||
-      IF_WIN(my_strchr(files_charset_info, udf->dl,
-                       udf->dl + strlen(udf->dl), '/'), 0))
+  if (check_valid_path(udf->dl, strlen(udf->dl)))
   {
     my_message(ER_UDF_NO_PATHS, ER(ER_UDF_NO_PATHS), MYF(0));
     DBUG_RETURN(1);