[Bug 1723956] Re: busybox-static: several network applets segfaulting

[Simon Rettberg]

Sure, here we go. It might be worth to note that this system was
installed as 12.04 or 12.10 and dist-upgraded ever since, so maybe this
would explain some oddities, although in general everything works just
fine.

libc6:
  Installed: 2.24-9ubuntu2.2
  Candidate: 2.24-9ubuntu2.2
  Version table:
 *** 2.24-9ubuntu2.2 500
        500 http://ftp.fau.de/ubuntu zesty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu zesty-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.24-9ubuntu2 500
        500 http://ftp.fau.de/ubuntu zesty/main amd64 Packages


With trial and error I could identify that libnss-resolve seems to be the problem. Removing it from the hosts line in nsswitch fixes the issue. Probably not the best fix but at least it can fall back to the resolver stub via the localhost resolv.conf entry for some caching. Unfortunately I can't upgrade to 17.10 yet until end of January to do additional testing.

** Attachment added: "original (faulty) nsswitch.conf"
   https://bugs.launchpad.net/ubuntu/+source/busybox/+bug/1723956/+attachment/5022596/+files/nsswitch.conf

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https://bugs.launchpad.net/bugs/1723956

Title:
  busybox-static: several network applets segfaulting

Status in busybox package in Ubuntu:
  Incomplete

Bug description:
  On a fully up-to-date Ubuntu 17.04, running most applets from busybox-
  static that are network-related lead to a segfault. Example:

  $ busybox nslookup google.com 8.8.8.8
  Server:    8.8.8.8
  Segmentation fault

  $ busybox        
  BusyBox v1.22.1 (Ubuntu 1:1.22.0-19ubuntu2) multi-call binary.
  [...]

  $ apt-cache policy busybox
  busybox:
    Installed: (none)
    Candidate: 1:1.22.0-19ubuntu2
    Version table:
       1:1.22.0-19ubuntu2 500
          500 http://ftp.fau.de/ubuntu zesty/universe amd64 Packages

  $ dpkg -S /bin/busybox 
  busybox-static: /bin/busybox

  $ apt-cache policy busybox-static
  busybox-static:
    Installed: 1:1.22.0-19ubuntu2
    Candidate: 1:1.22.0-19ubuntu2
    Version table:
   *** 1:1.22.0-19ubuntu2 500
          500 http://ftp.fau.de/ubuntu zesty/main amd64 Packages
          100 /var/lib/dpkg/status


  This even happens when passing invalid domains or DNS servers to use
  that don't actually run any DNS service. (like "busybox nslookup
  google.com 1.2.3.4" or "busybox nslookup bar.foof00 8.8.8.8"), so it
  seems to be early in the network setup.

  I could not reproduce the problem on the very same system when compiling stock busybox 1.22.1 (why even? we're at 1.27.x!) myself, neither with a recent git clone. Also two VMs I had at hand running Ubuntu 14.04 and 16.04 didn't show this problem with busybox-static. Installing the package "busybox" (which removes busybox-static) fixes the problem on 17.04.
  The only thing that might be related in any way about my system is that it has no IPv6 connectivity (apart from the link-local address).

  I also sent a crash report when the apport window popped up, but I
  have no idea where this ends up and how to add further information,
  hence this report here. Please let me know if this seemingly trivial
  bug cannot be reproduced instantly, so I can try to assist with
  further information.

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