https://bugzilla.redhat.com/show_bug.cgi?id=480420#c17 Here is some background information of how this happened. A long standing bug in NFS since August 2000 is that it did not support tcp wrappers /etc/hosts.deny and /etc/hosts.allow. This was fixed upstream, but then they discovered an issue. /etc/hosts.deny: mountd: badhost.example.com If DNS is down or the source IP address lacks a reverse lookup, then it has no way of knowing that it is meant to be denied. It allows the connection. This was considered to a be an unacceptable bug. If someone specifies a hostname, from a security perspective they expect the failure case to err to the side of caution and deny by default if cannot affirm that the incoming client is not a listed denied hostname. Thus "deny upon reverse DNS failure" became the default behavior in nfs-utils. This manifested in F-9 and F-10 with a many people suddenly unable to NFS mount after nfs-utils update hit mirrors ~January 14th. This is especially problematic in cases where people use caching DNS nameservers, as it is non-trivial to explain to everyone how to setup a proper DNS for arbitrary addresses. These individuals might also have no control over DNS on their network. I believe that "hostname in /etc/hosts.deny fails to deny" should be NOTABUG for several reasons: * BAD POLICY and MISCONFIGURATION. TCP wrappers is behaving exactly how it is defined in policy. Hostname in hosts.deny (itself always a bad idea) is dependent on the DNS server to be properly configured and operating. Failure due to hostnames in /etc/hosts.deny is MISCONFIGURATION. If they are really concerned about unknown clients connecting to that service, then they should use a wildcard like "mountd: ALL" and allow specific hosts or IP ranges in /etc/hosts.allow. * Host names in iptables or tcp wrappers rules are ALWAYS a bad idea because you are relying upon an unreliable and insecure external data source that is DNS. DNS can be too easily spoofed, hijacked, denial of service attacked, and it lacks any semblance of authentication or encryption. * It is wrong for a service wrapped by tcp wrappers to over-engineer itself to workaround misconfiguration on the part of the sysadmin. * It is inconsistent with the behavior of any other service wrapped by tcp wrappers. "sshd: badhost.example.com" allows incoming connections if reverse DNS lookup fails. Does this mean sshd and every other service wrapped by tcp wrappers should also be modified? * This is inconsistent with iptables. "iptables -A INPUT -p tcp --dport 22 -s badhost.example.com -j REJECT" might also fail to reject an incoming connection under similar DNS-related conditions. It would be clearly wrong for sshd to second-guess and parse iptables rules, and make its own decision based its own reverse DNS query matching hostnames found in those iptables rules. Why is it OK to second guess tcp wrappers but not iptables? * Even if we agree that this is a bug that should be fixed and not simply sysadmin misconfiguration, the correct layer to fix it is in tcp wrappers itself, not the individual wrapped services. We had a lengthy discussion and have come to reluctant agreement on how to proceed from here. It was decided by the filesystem people that even if it is only the result of misconfiguration, nfs-utils should protect and deny by default. Steve is working on the next build of nfs-utils with slightly different logic. It will behave exactly as it did before this change (no tcp wrappers or deny on reverse DNS lookup failure). It will only enable tcp wrapper and the new denial behavior if any mountd, statd or wildcard lines appear in /etc/hosts.deny or /etc/hosts.allow. We will hopefully have a new build tomorrow. Workarounds until this is fixed... ================================== 1) Remove tcpwrappers (if you don't need quotas this might be OK) 2) Downgrade nfs-utils to these versions: http://kojipkgs.fedoraproject.org/packages/nfs-utils/1.1.2/7.fc9/ http://kojipkgs.fedoraproject.org/packages/nfs-utils/1.1.4/4.fc10/ 3) For LTSP users, you can opt to stop using NFS entirely. LTSP users can switch to NBD instead, which is a little more work, but clients boot a little faster. https://fedorahosted.org/k12linux/NBDRootConfiguration Warren Togami wtogami@xxxxxxxxxx -- fedora-devel-list mailing list fedora-devel-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/fedora-devel-list
