Baffling SSH/SCP problem continues - any gurus around?

From: Steve Linberg (slinberg@crocker.com)
Date: 06/20/02 

From: Steve Linberg <slinberg@crocker.com>
Date: Thu, 20 Jun 2002 03:46:58 GMT

I'm still stuck on a problem I'm having that started about 3 months ago;
I've spent all day working on it today and must wearily confess that I
have no clue what's wrong at this point.

It's the same problem I discussed with Nico in early April (google:
<http://groups.google.com/groups?threadm=slinberg-46446E.10105406042002%4
0netnews.attbi.com>), where I started experiencing corruption when using
scp to transfer files from my RH 6.2 server I had recently upgraded. I
had rebuilt both openssh and openssl from source (as I always had
earlier as well), and scp started breaking.

Nico urged me not to build from source, but to use RPMs instead;
however, the RPMs for Red Hat 6.x are abysmally old, and I also wanted
(and still want) to understand what the nature of the corruption is.
Today I rebuilt them both again (openssl 0.9.6d and openssh 3.2.3p1),
and still, although ssh to the server works fine, scp is still broken.

I have more detail on "broken" as far as scp goes: when I try to scp a
file down from the server (and I've tried on many different clients),
the file transfers never end; from what I can tell, the last 2048 bytes
in the file keep getting sent over and over, and the local file grows
and grows until the local scp process is interrupted (e.g. with
control-C). A cursory glance at scp.c shows that 2048 is a
frequently-used buffer size, so that's got to be a clue.

I've set up another machine (a PIII, like my "real" server, serving as a
testbed) with as close as I could get to the same environment; same
version of Red Hat, same versions of glibc and egcs and zlib (all RPMs),
same partitioning, directory layouts, and everything else I can think
of. With the same compiler flags and the same configure / install /
build steps, openssl and openssh work just fine on the local machine.
scp does too. No problems.

I downloaded the suspect binary of sshd from the "real" server and
installed it on the local version and rebooted, when I tried to scp an
exact copy of the file I've been testing with from the local server
running the sshd from the "real" server, it worked. This seems to me to
rule out any problem with the build of openssh, right? The same binary
worked on my local machine, but not on the remote machine.

Finally, I tried using scp to copy a file on the remote server to
itself, and got the same problem - the last 2048 bytes being resent over
and over. ("scp me@my_server_ip:patch.txt .")

So something else is hideously wrong, perhaps with my live server's
configuration somewhere - but I haven't got a clue where to look at this
point. As far as I can tell, everything's running fine on that server -
apache, mysql, perl, etc - and I can ssh in just fine and do everything
I normally do. No signs of anything abnormal.

If anyone can suggest a next step (that doesn't involve nuking the
server and starting over, it's live and I can't take it down for
rebuilding because I don't have and can't afford a second/backup server
to colocate), I'd be deeply appreciative. I get the feeling that
there's a very important lesson waiting in this one, somewhere deep down.

Cheers,

Steve Linberg

Relevant Pages

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  • Re: Baffling SSH/SCP problem continues - any gurus around?
    ... > scp to transfer files from my RH 6.2 server I had recently upgraded. ... > and still, although ssh to the server works fine, scp is still broken. ... With the same compiler flags and the same configure / install / ... openssl and openssh work just fine on the local machine. ...
    (comp.security.ssh)
  • Re: Baffling SSH/SCP problem continues - any gurus around?
    ... > scp to transfer files from my RH 6.2 server I had recently upgraded. ... > and still, although ssh to the server works fine, scp is still broken. ... With the same compiler flags and the same configure / install / ... openssl and openssh work just fine on the local machine. ...
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