Bug#39277 - symlink.test fails on Debian

      
When the data directory contained a symbolic link to another
file system, and the DATA or INDEX DIRECTORY clause of a
CREATE TABLE statement referred to a subdirectory of the data
directory, this was accepted.
      
The problem was the use of a table file path name, which included
the table name without an extension, for the comparison against
the data directory path name. This was almost always a
non-existent file. The internal algorithm failed to resolve
symbolic links for non-existent files. So we compared unrelated
path names.
      
Fixed by truncating the table name from the path before resolving
symlinks. If this is also a non-existent path, the creation of
the table will fail anyway.

Backport to 5.6.0.    6.0-codebase revid: 2599.60.1

sql/sql_table.cc

@@ -3934,15 +3934,43 @@ bool mysql_create_table_no_lock(THD *thd,
   create_info->table_existed= 0;		// Mark that table is created
 
 #ifdef HAVE_READLINK
-  if (test_if_data_home_dir(create_info->data_file_name))
   {
-    my_error(ER_WRONG_ARGUMENTS, MYF(0), "DATA DIRECTORY");
-    goto unlock_and_end;
-  }
-  if (test_if_data_home_dir(create_info->index_file_name))
-  {
-    my_error(ER_WRONG_ARGUMENTS, MYF(0), "INDEX DIRECTORY");
-    goto unlock_and_end;
+    size_t dirlen;
+    char   dirpath[FN_REFLEN];
+
+    /*
+      data_file_name and index_file_name include the table name without
+      extension. Mostly this does not refer to an existing file. When
+      comparing data_file_name or index_file_name against the data
+      directory, we try to resolve all symbolic links. On some systems,
+      we use realpath(3) for the resolution. This returns ENOENT if the
+      resolved path does not refer to an existing file. my_realpath()
+      does then copy the requested path verbatim, without symlink
+      resolution. Thereafter the comparison can fail even if the
+      requested path is within the data directory. E.g. if symlinks to
+      another file system are used. To make realpath(3) return the
+      resolved path, we strip the table name and compare the directory
+      path only. If the directory doesn't exist either, table creation
+      will fail anyway.
+    */
+    if (create_info->data_file_name)
+    {
+      dirname_part(dirpath, create_info->data_file_name, &dirlen);
+      if (test_if_data_home_dir(dirpath))
+      {
+        my_error(ER_WRONG_ARGUMENTS, MYF(0), "DATA DIRECTORY");
+        goto unlock_and_end;
+      }
+    }
+    if (create_info->index_file_name)
+    {
+      dirname_part(dirpath, create_info->index_file_name, &dirlen);
+      if (test_if_data_home_dir(dirpath))
+      {
+        my_error(ER_WRONG_ARGUMENTS, MYF(0), "INDEX DIRECTORY");
+        goto unlock_and_end;
+      }
+    }
   }
 
 #ifdef WITH_PARTITION_STORAGE_ENGINE