Created attachment 335181 [details] netkit-telnet-0.17-reallynodns.patch Description of problem: telnetd exits, closing the incoming connection, when the local host name is not in the DNS. Version-Release number of selected component (if applicable): telnet-server-1:0.17-43.fc10.x86_64 How reproducible: Always Steps to Reproduce: 1. yum install telnet-server 2. vi /etc/xinetd.d/telnet and set disabled=no 3. chkconfig telnet restart 4. sudo hostname this-host-is-not-in-dns 5. telnet localhost Actual results: Connected to localhost. Escape character is '^]'. getaddrinfo: localhost Name or service not known Connection closed by foreign host. Expected results: I expected to get a login prompt. Additional info: This problem was introduced by netkit-telnet-0.17-ipv6.patch, and is somewhat mitigated by netkit-telnet-0.17-nodns.patch. The original netkit-telnet code simply ignores any kind of host lookup failure when trying to canonify the local hostname; the ipv6 patch switches to using getaddrinfo but does not actually use the results other than to exit with an error when the name server is unreachable or the host does not exist. The nodns patch modifies the ipv6 patch to accept the case where the name server is unreachable but still exits if the host does not exist. It retains the ipv6 patch's behavior of not canonifying the hostname. In most modern configurations, the hostname is already canonical, so this code is extraneous. In addition, the local hostname itself is very rarely used, whether it's canonical or not. The name is used in auth_encrypt_init(), which appears to stash it in a global variable and never used again, and is used to substitute for \h or \n in /etc/issue.net. I've attached a patch, netkit-telnet-0.17-reallynodns.patch, which: 1) Adds an argument, -N, to telnetd, to suppress this lookup, for an environment where, e.g., you don't care whether the name is fully canonical and you don't want to pay for the DNS resolution even if everything is OK; and 2) Restores the behavior of canonifying the hostname (e.g., bs23 -> bs23.aristanetworks.com) if -N is not specified (but continuing on with the gethostname() result if the lookup fails for any reason, as the original netkit code did). Since it overlaps with both -ipv6.patch and -nodns.patch, I'd be happy to generate a new version that replaces one or both of those patch files instead of repeatedly patching the same set of lines.
Forgot to demonstrate that the current version does not canonify the hostname. Here is what \h and \n are set to when running telnet-server-1:0.17-42.fc9.x86_64: ~/src/telnet-f11 @bs23> sudo hostname bs23 ~/src/telnet-f11 @bs23> telnet localhost Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. Fedora release 10 (Cambridge) Kernel 2.6.28-0.116026.2006.Arora.fc10.x86_64 on an x86_64 (25) My hostname is bs23 My name is bs23 login: After installing my patched version: ~/src/telnet-f11 @bs23> sudo rpm -U /RPMS/telnet-server.x86_64.rpm ~/src/telnet-f11 @bs23> telnet localhost Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. Fedora release 10 (Cambridge) Kernel 2.6.28-0.116026.2006.Arora.fc10.x86_64 on an x86_64 (25) My hostname is bs23.aristanetworks.com My name is bs23.aristanetworks.com login:
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Sorry for mis-filling the version field. This applies to F10 (I tested against telnet-server-1:0.17-43.fc10.x86_64) and at the time of reporting I downloaded the srpm that was going into F11, and tested that on F10 and the behavior is the same.
Thanks for the patch and detailed inspection about the problem. Fixed in telnet-0.17-45.fc12. If you would like to have this issue fixed in F11 as well please reopen this bug.
Please port this bug fix to F11. Please keep in mind that F11 is the last Fedora to support i586 CPUs. You can install F12 on i586. This means that F11 have to exist as long as i586 class Pentium cpus exist.
(In reply to comment #6) > Please port this bug fix to F11. > > Please keep in mind that F11 is the last Fedora to support i586 CPUs. You can > install F12 on i586. This means that F11 have to exist as long as i586 class > Pentium cpus exist. I meant to say you can't install F12 on i586 class Pentium.
This problem seems to be even greater on networks with consumer grade routers where there is no local DNS.