openssh bugs - May 2004 - [Bug 861] Swapped parameters of SSH_FXP_SYMLINK packet of SFTP protocol

http://bugzilla.mindrot.org/show_bug.cgi?id=861

           Summary: Swapped parameters of SSH_FXP_SYMLINK packet of SFTP
                    protocol
           Product: Portable OpenSSH
           Version: -current
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: sftp-server
        AssignedTo: openssh-bugs at mindrot.org
        ReportedBy: opensshbugzilla at prikryl.cz


Hello,

I'm developer of WinSCP (SCP/SFTP client for Windows).
I have just realised that my client is probably sending parameters linkpath and 
targetpath of SFTP SSH_FXP_SYMLINK packet in incorrect order. What has 
surprised me is that despite this, it works fine with all OpenSSH SFTP servers. 
Well otherwise I would have noticed earlier :-) This made me believe that 
OpenSSH SFTP server has the same bug.
Ssh.com SFTP server obviously adheres to the standards, so with it my client 
cannot create the links.

Can you confirm this?

http://www.openssh.org/txt/draft-ietf-secsh-filexfer-02.txt

The SSH_FXP_SYMLINK request will create a symbolic link on the
server.  It is of the following format

   	uint32     id
   	string     linkpath
   	string     targetpath

The latest (CVS) sftp-server.c:

873:    oldpath = get_string(NULL);
874:    newpath = get_string(NULL);
875:    TRACE("symlink id %u old %s new %s", id, oldpath, newpath);
876:    /* this will fail if 'newpath' exists */
877:    ret = symlink(oldpath, newpath);

The same bug is obviously even in OpenSSH SFTP client:
The latest (CVS) sftp-client.c:

647:    id = conn->msg_id++;
648:    buffer_put_char(&msg, SSH2_FXP_SYMLINK);
649:    buffer_put_int(&msg, id);
650:    buffer_put_cstring(&msg, oldpath);
651:    buffer_put_cstring(&msg, newpath);

Have a nice day.

Martin Prikryl
http://www.prikryl.cz/
http://winscp.sourceforge.net/



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http://bugzilla.mindrot.org/show_bug.cgi?id=861

dtucker at zip.com.au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED



------- Additional Comments From dtucker at zip.com.au  2004-05-12 12:40 -------
Yep, that looks like a bug to me.  I suspect the confusion is due to
SSH_FXP_SYMLINK having its arguments in the opposite order to the equivalent
Unix "ln" command, whereas other (eg FXP_RENAME) are the same as their
equivalents.

The next question is what to do about it, and when?  AFAIK, sftp doesn't
know
what SSH server is on the other end, except for the SFTP protocol version (it
just runs "ssh -s host sftp").  Maybe fix it next time the protocol
version
supported is bumped?



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------- Additional Comments From opensshbugzilla at prikryl.cz  2004-05-12 17:52
-------
Are there any plans to support newer version of SFTP? You support version 3, 
while there is version 5 draft published already.

BTW: version 5 has mechanism to detect version of SFTP server software (not 
SFTP protocol version).

Possible (maybe dirty) workaround would be to utilize SFTP extension to let the 
client know if the bug is fixed already. But it would not solve problem when 
other vendors's client connects to your server.



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