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().

1 files changed, 22 insertions, 1 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)