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Bug 668993 - Xforwarding only works by adding -4 to sshd_config
Summary: Xforwarding only works by adding -4 to sshd_config
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: openssh
Version: 6.0
Hardware: x86_64
OS: Linux
low
low
Target Milestone: rc
: ---
Assignee: Jan F. Chadima
QA Contact: BaseOS QE Security Team
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2011-01-12 11:41 UTC by Andre ten Bohmer
Modified: 2011-05-26 13:19 UTC (History)
1 user (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2011-05-26 13:19:23 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)

Description Andre ten Bohmer 2011-01-12 11:41:25 UTC 
Description of problem:
Connecting from a linux client to an up-to-date Redhat EL 6 server with sshd Xforwarding configured, actually fails to perform Xforwarding. Server only has ipv4 configured, no ipv6.

After adding 
OPTIONS="-4"
to /etc/sysconfig/sshd and a sshd service restart, Xforwarding works.

Version-Release number of selected component (if applicable):
openssh-server-5.3p1-20.el6_0.3.x86_64

How reproducible:

Steps to Reproduce:
1. ssh -X redhat6.server.org

Actual results:
]$ xeyes 
Error: Can't open display: 

Expected results:
Xeyes popping up on Linux client

Additional info:
- sshd debug info
debug1: session_input_channel_req: session 0 req x11-req
Failed to allocate internet-domain X11 display socket.
debug1: x11_create_display_inet failed.
debug1: server_input_channel_req: channel 0 request pty-req reply 1
debug1: session_by_channel: session 0 channel 0
debug1: session_input_channel_req: session 0 req pty-req

- sshd_config
Port 22
ListenAddress 0.0.0.0
Protocol 2
SyslogFacility AUTHPRIV
PasswordAuthentication yes
ChallengeResponseAuthentication no
GSSAPIAuthentication yes
GSSAPICleanupCredentials yes
UsePAM yes
AcceptEnv LANG LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGES
AcceptEnv LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENT
AcceptEnv LC_IDENTIFICATION LC_ALL LANGUAGE
AcceptEnv XMODIFIERS
X11Forwarding yes
Subsystem	sftp	/usr/libexec/openssh/sftp-server
PermitRootLogin no
KeepAlive yes
ClientAliveInterval 15
ClientAliveCountMax 3
AllowGroups sshlogon

- /etc/sysctl.conf
net.ipv6.conf.all.disable_ipv6 = 1
Comment 2 RHEL Program Management 2011-04-04 01:54:06 UTC 
Since RHEL 6.1 External Beta has begun, and this bug remains
unresolved, it has been rejected as it is not proposed as
exception or blocker.

Red Hat invites you to ask your support representative to
propose this request, if appropriate and relevant, in the
next release of Red Hat Enterprise Linux.
Comment 3 Jan F. Chadima 2011-04-07 12:50:14 UTC 
Trying to reproduce... Can tunnel X11 from ipv6 server when X11UseLocalhost is set to yes. Otherwise it does not work and report to syslog:
error: Failed to allocate internet-domain X11 display socket.
Will investigate later.
Comment 4 Jan F. Chadima 2011-04-11 06:23:43 UTC 
Reporter, plase, can you test the last RHEL6.1 package with explicitly enabled X11UseLocalhost yes?
Comment 5 Andre ten Bohmer 2011-04-11 07:33:42 UTC 
Jan, would you be so kind to point me in the right direction to download the RHEL6.1 package? Should I subscribe the system to the RHN RH6 beta channel?
Comment 6 Alexander Boström 2011-04-11 14:49:49 UTC 
I had the same problem but noticed that /etc/hosts was empty (for whatever reason..). Adding

127.0.0.1       localhost.localdomain   localhost
::1             localhost6.localdomain6 localhost6

solved the problem. (Client and server here are dual-stack with A and AAAA records.)

openssh-server-5.3p1-45.el6.x86_64
(yes, subscribed to a beta channel)

X11UseLocalhost was commented out.
Comment 7 Jan F. Chadima 2011-04-12 04:47:48 UTC 
(In reply to comment #6)
> 
> X11UseLocalhost was commented out.
the default value  should be yes
Comment 8 Jan F. Chadima 2011-05-24 18:09:04 UTC 
Have you still the problem?
Comment 9 Andre ten Bohmer 2011-05-26 12:32:50 UTC 
Fresh installed a RHELS 6.1 x64 and X-Forwarding works without having to apply previous modifications. Thanks!
Comment 10 Jan F. Chadima 2011-05-26 13:19:23 UTC 
reporter found that there is no longer the bug
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