race-condition safe implementation of test_if_data_home_dir()

don't realpath() twice

sql/mysqld.cc

@@ -7267,7 +7267,7 @@ static int mysql_init_variables(void)
   mysql_home[0]= pidfile_name[0]= log_error_file[0]= 0;
 #if defined(HAVE_REALPATH) && !defined(HAVE_valgrind) && !defined(HAVE_BROKEN_REALPATH)
   /*  We can only test for sub paths if my_symlink.c is using realpath */
-  mysys_test_invalid_symlink= test_if_data_home_dir;
+  mysys_test_invalid_symlink= path_starts_from_data_home_dir;
 #endif
   opt_log= opt_slow_log= 0;
   opt_bin_log= opt_bin_log_used= 0;

sql/sql_parse.cc

@@ -7697,26 +7697,20 @@ bool check_ident_length(LEX_STRING *ident)
   Check if path does not contain mysql data home directory
 
   SYNOPSIS
-    test_if_data_home_dir()
-    dir                     directory
+    path_starts_from_data_home_dir()
+    dir                     directory, with all symlinks resolved
 
   RETURN VALUES
     0	ok
     1	error ;  Given path contains data directory
 */
-C_MODE_START
+extern "C" {
 
-int test_if_data_home_dir(const char *dir)
+int path_starts_from_data_home_dir(const char *path)
 {
-  char path[FN_REFLEN];
-  int dir_len;
-  DBUG_ENTER("test_if_data_home_dir");
+  int dir_len= strlen(path);
+  DBUG_ENTER("path_starts_from_data_home_dir");
 
-  if (!dir)
-    DBUG_RETURN(0);
-
-  (void) fn_format(path, dir, "", "", MY_RETURN_REAL_PATH);
-  dir_len= strlen(path);
   if (mysql_unpacked_real_data_home_len<= dir_len)
   {
     if (dir_len > mysql_unpacked_real_data_home_len &&
@@ -7744,7 +7738,31 @@ int test_if_data_home_dir(const char *dir)
   DBUG_RETURN(0);
 }
 
-C_MODE_END
+}
+
+/*
+  Check if path does not contain mysql data home directory
+
+  SYNOPSIS
+    test_if_data_home_dir()
+    dir                     directory
+
+  RETURN VALUES
+    0	ok
+    1	error ;  Given path contains data directory
+*/
+
+int test_if_data_home_dir(const char *dir)
+{
+  char path[FN_REFLEN];
+  DBUG_ENTER("test_if_data_home_dir");
+
+  if (!dir)
+    DBUG_RETURN(0);
+
+  (void) fn_format(path, dir, "", "", MY_RETURN_REAL_PATH);
+  DBUG_RETURN(path_starts_from_data_home_dir(path));
+}
 
 
 /**

sql/sql_parse.h

@@ -33,7 +33,8 @@ enum enum_mysql_completiontype {
   COMMIT_RELEASE=-1,   COMMIT=0,    COMMIT_AND_CHAIN=6
 };
 
-extern "C" int test_if_data_home_dir(const char *dir);
+extern "C" int path_starts_from_data_home_dir(const char *dir);
+int test_if_data_home_dir(const char *dir);
 
 bool multi_update_precheck(THD *thd, TABLE_LIST *tables);
 bool multi_delete_precheck(THD *thd, TABLE_LIST *tables);