I have a linux dns server/smtp server that I configured. I would eventually remove the mouse, keyboard and monitor and hide the box somewhere and leave it running all the time. I installed the latest openssl and openssh package by source (I am running Redhat 5.2). I find that I can only remote login if I login as root. If I login as any other user, the connection to the linux box is closed by remote host. This happens even If I try to ssh locally with ssh -l user localhost. If I look at the logs I see password authentication succeeded
channel 0: new [client-session]
channel 0: send open
Entering interactive session
callback start
ssh_session2_setup:id 0
channel 0:request pty-req
channel 0:request shell
callback done
channel 0: open confirm rwindow - rmax 32768
channel_free: channel 0: client-session,nchannels 1
Connection to localhost closed by remote host
Connection to localhost closed.
Transferred : stdin 0, stdout 0, stderr 81 bytes in 0.4 seconds
Bytes per second: stdin 0.0, stdout 0.0, stderr 217.1
Exit status -1

In /var/log/messages I see:
Accepted password for user from 127.0.0.1 port 104 ssh2
fatal : mm_receive_fd : expected type 1 got 10443377

If I login as root, everything is fine loggin in remotely or locally. Thanks for any help you can give.

http://www.der-keiler.de/Mailing-Lis...2-12/0005.html

What happens if you turn off privelege seperation and restart sshd?

Thank You Very Much!
I deleted the sshd priv sep user and group and then disabled it in sshd_config. User can now log on. You just saved me countless hours of figuring out.

I hope you realize privsep makes part of sshd run as root, and part in a chroot. By disabling privsep you're effectively weakening your boxes security posture by making the whole of sshd run as root. IMHO a good way to assess/curb risks would be to review the restrictions you place on remote access (if you can) using the directives in sshd_config, TCP Wrappers and the firewall.

Followint the above link by m0rl0ck, it seems that the problem is with the 2.0.x linux kernel. If so is it even fixable? Thanks

IIRC it's an mmap related issue in 2.2x and below, but you'd better read up on these discussions in any mailinglist archiving site like Neohapsis.com or Der-keiler.de.