[erlang-questions] SFTPD, directory listing and file attributes

[Karolis Petrauskas]

I have referred to a wrong version of the protocol specification.
https://tools.ietf.org/html/draft-ietf-secsh-filexfer-03 describes
protocol version 4.
The version 3 is described in
https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02.
This explains why the existing code works at all :)

However, I still don't know, why sftp client shows the directory
listing without the attributes.

Karolis


On Thu, Dec 28, 2017 at 12:49 AM, Karolis Petrauskas
<k.petrauskas@REDACTED> wrote:
> Hi all,
>
> I'm trying to use the ssh_sftpd server and found strange behaviour
> when listing files:
>
>     sftp> ls -l /c/
>     data.csv
>     data.txt
>     some.xxx
>
> File permissions and gid/uid are not shown with the -l option.
>
> If listing the files with the -n option the file attributes are shown
> as expected:
>
>     sftp> ls -n /c/
>     -rw-rw-r--    0 1000     1000            0 Dec 27 20:11 /c/data.csv
>     -rw-rw-r--    0 1000     1000            0 Dec 27 20:12 /c/data.txt
>     -rw-rw-r--    0 1000     1000            0 Dec 27 19:12 /c/some.xxx
>
> The attributes are also shown if the files are listed using wildcard:
>
>     sftp> ls -l /c/*
>     -rw-rw-r--    0 1000     1000            0 Dec 27 20:12 /c/data.txt
>     -rw-rw-r--    0 1000     1000            0 Dec 27 20:11 /c/data.csv
>     -rw-rw-r--    0 1000     1000            0 Dec 27 19:12 /c/some.xxx
>
> But in this case, the sftp client asks for file attributes for each
> file explicitly. In the client debug, I see the calls similar to the
> following, repeated three times in this case:
>
>     debug3: Sent message fd 3 T:7 I:20
>     debug3: Received stat reply T:105 I:20
>
>
> I work on linux, Ubuntu xenial.
> I use Erlang/OTP 20.1 for the server.
> The client is openssh sftp, version="OpenSSH_7.2p2 Ubuntu-4ubuntu2.2,
> OpenSSL 1.0.2g  1 Mar 2016".
> The server and the client agrees on the sftp version 3, as the client
> implements it.
>
> I tried to look at the ssh_sftp server sources. It looks like
> ssh_xfer:encode_name/3 is incorrect, because long file name is not
> included in the protocol version 3
> (https://tools.ietf.org/html/draft-ietf-secsh-filexfer-03#page-26, see
> SSH_FXP_NAME).
> As I quick test, I tried to change the Vsn ranges here, but in that
> case the server started to report corrupted frames.
>
> I would be apprieciated for any pointers.
>
> Maybe there is a way to log the sftp messages (decrypted) on the
> client, it would help to compare responses from the erlang server and
> the openssh server (the latter provides the attributes correctly).
>
> --
> Karolis Petrauskas