openssh bugs - Dec 2004 - [Bug 934] Traverse-only directories (e.g. chmod 110) break the cd command in sftp

http://bugzilla.mindrot.org/show_bug.cgi?id=934

djm at mindrot.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|sftp-server                 |sftp
            Version|3.6.1p2                     |-current



------- Additional Comments From djm at mindrot.org  2004-12-06 17:13 -------
Yes, this problem is known (it is actually in the client) but is a little tricky
to fix. 

Basically the sftp client does a realpath() to verify that a path is accessible
and to change relative paths into absolute ones, but realpath breaks on traverse
only directories. 

The solution is to modify the client to fall back to doing a stat() on the path
when the realpath() fails. The client can then just continue, using a relative
path.

This isn't particularly nice either, because it adds another round-trip for
each
"cd" command (only on realpath error though)



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http://bugzilla.mindrot.org/show_bug.cgi?id=934





------- Additional Comments From mgjk at idirect.com  2004-12-12 01:21 -------
That's makes sense, so realpath() breaks in sftp-server because sftp-server
is
running as the user, whereas FTP servers are not quite so diligent about
security?



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------- Additional Comments From djm at mindrot.org  2004-12-12 09:13 -------
Not quite: most ftp server can actually do a chdir() to set the current working
directory. The sftp protocol doesn't even have the concept of a
"current working
directory", so our implementation uses realpath() to convert between the
paths
that the user types (which may be relative) and absolute filesystem paths. 

This conversion isn't 100% necessary, and it may be possible to skip it in
some
cases - e.g. when realpath() fails



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