BUG#32111 - Security Breach via DATA/INDEX DIRECORY and RENAME TABLE

RENAME TABLE against a table with DATA/INDEX DIRECTORY overwrites
the file to which the symlink points.

This is security issue, because it is possible to create a table with
some name in some non-system database and set DATA/INDEX DIRECTORY
to mysql system database. Renaming this table to one of mysql system
tables (e.g. user, host) would overwrite the system table.

Return an error when the file to which the symlink points exist.

mysql-test/r/symlink.result

@@ -84,3 +84,9 @@ t1	CREATE TABLE `t1` (
   `b` int(11) default NULL
 ) TYPE=MyISAM
 drop table t1;
+CREATE TABLE t1(a INT)
+DATA DIRECTORY='TEST_DIR/var/master-data/mysql'
+INDEX DIRECTORY='TEST_DIR/var/master-data/mysql';
+RENAME TABLE t1 TO user;
+Can't create/write to file 'TEST_DIR/var/master-data/mysql/user.MYI' (Errcode: 17)
+DROP TABLE t1;

mysql-test/t/symlink.test

@@ -112,3 +112,15 @@ eval alter table t1 index directory="$MYSQL_TEST_DIR/var/log";
 enable_query_log;
 show create table t1;
 drop table t1;
+
+#
+# BUG#32111 - Security Breach via DATA/INDEX DIRECORY and RENAME TABLE
+#
+--replace_result $MYSQL_TEST_DIR TEST_DIR
+eval CREATE TABLE t1(a INT)
+DATA DIRECTORY='$MYSQL_TEST_DIR/var/master-data/mysql'
+INDEX DIRECTORY='$MYSQL_TEST_DIR/var/master-data/mysql';
+--replace_result $MYSQL_TEST_DIR TEST_DIR
+--error 1
+RENAME TABLE t1 TO user;
+DROP TABLE t1;

mysys/my_symlink2.c

@@ -120,6 +120,7 @@ int my_rename_with_symlink(const char *from, const char *to, myf MyFlags)
   int was_symlink= (!my_disable_symlinks &&
 		    !my_readlink(link_name, from, MYF(0)));
   int result=0;
+  int name_is_different;
   DBUG_ENTER("my_rename_with_symlink");
 
   if (!was_symlink)
@@ -128,6 +129,14 @@ int my_rename_with_symlink(const char *from, const char *to, myf MyFlags)
   /* Change filename that symlink pointed to */
   strmov(tmp_name, to);
   fn_same(tmp_name,link_name,1);		/* Copy dir */
+  name_is_different= strcmp(link_name, tmp_name);
+  if (name_is_different && !access(tmp_name, F_OK))
+  {
+    my_errno= EEXIST;
+    if (MyFlags & MY_WME)
+      my_error(EE_CANTCREATEFILE, MYF(0), tmp_name, EEXIST);
+    DBUG_RETURN(1);
+  }
 
   /* Create new symlink */
   if (my_symlink(tmp_name, to, MyFlags))
@@ -139,7 +148,7 @@ int my_rename_with_symlink(const char *from, const char *to, myf MyFlags)
     the same basename and different directories.
    */
 
-  if (strcmp(link_name, tmp_name) && my_rename(link_name, tmp_name, MyFlags))
+  if (name_is_different && my_rename(link_name, tmp_name, MyFlags))
   {
     int save_errno=my_errno;
     my_delete(to, MyFlags);			/* Remove created symlink */