[Bug 2060150] [NEW] openssh sets PAM_RHOST to UNKNOWN causing slow logins

[Luca Boccassi]

Public bug reported:

When using sshd's -i option with stdio that is not a AF_INET/AF_INET6
socket, auth_get_canonical_hostname() returns "UNKNOWN" which is then
set as the value of PAM_RHOST, causing pam to try to do a reverse DNS
query of "UNKNOWN", which times out multiple times, causing a
substantial slowdown when logging in.

upstream PR: https://github.com/openssh/openssh-portable/pull/388
upstream email: https://lists.mindrot.org/pipermail/openssh-unix-dev/2024-April/041289.html
Fedora backport: https://src.fedoraproject.org/rpms/openssh/pull-request/71
Debian backport: https://salsa.debian.org/ssh-team/openssh/-/merge_requests/25

** Affects: openssh (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2060150

Title:
  openssh sets PAM_RHOST to UNKNOWN causing slow logins

Status in openssh package in Ubuntu:
  New

Bug description:
  When using sshd's -i option with stdio that is not a AF_INET/AF_INET6
  socket, auth_get_canonical_hostname() returns "UNKNOWN" which is then
  set as the value of PAM_RHOST, causing pam to try to do a reverse DNS
  query of "UNKNOWN", which times out multiple times, causing a
  substantial slowdown when logging in.

  upstream PR: https://github.com/openssh/openssh-portable/pull/388
  upstream email: https://lists.mindrot.org/pipermail/openssh-unix-dev/2024-April/041289.html
  Fedora backport: https://src.fedoraproject.org/rpms/openssh/pull-request/71
  Debian backport: https://salsa.debian.org/ssh-team/openssh/-/merge_requests/25

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