Relative TFTP path resolution

[Angus Gratton]

Using RTEMS 4.10, it looks like there's no generic filesystem support
for relative paths that include the ".." previous directory signifier.

For instance, if my TFTP filesystem looks like:

        /
        /dirA/
        /dirB/
        /dirB/file.txt
        
and I issue something like

        chdir("/TFTP/HOST/dirA/");
        open("../dirB/file.txt");

then my TFTP server sees a request for "/dirA/dirB/file.txt", which is
not what I expected.


Looking in the code, it's not entirely clear whether the abstraction to
support this should be implemented generally under
rtems_filesystem_evaluate_path(), or be delegated to each filesystem
type, so in this case rtems_tftp_eval_path().

At present the path with "../" prepended makes it all the way to
tftp_eval_path, but then a custom fixPath() function strips it off.


I can see a couple of ways that you could try to implement this, but
none of them seem to fit neatly into the current design around
rtems_filesystem_location_info_t. Which is why I thought I'd ask if
anyone has any tips?

If possible, I'd rather not have a hack that sends my TFTP server
"/dirA/../dirB/file.txt". In my case, atftpd (correctly) does not accept
this kind of path, because the server doesn't run chrooted and therefore
it's a security hole.

Does anyone have any guidance for me? Has this been improved or changed
in more recent versions?

Thanks in advance.

Cheers,

Angus