[Bug 1714803] Re: Search list in resolv.conf breaks resolving for that domain

[Matthias Fratz]

I can confirm that the underlying bug still exists in today's artful
nightly CD.

I wasn't able to get a search path to stick in /etc/resolv.conf, but
setting Domains=ubuntu.com in /etc/systemd/resolved.conf triggers the
same bug: It breaks resolution for ubuntu.com and www.ubuntu.com (and
probably all other subdomains as well), and www doesn't resolve either.
nslookup reports SERVFAIL; systemd-resolve reports "No appropriate name
servers or networks for name found".

Testing this on my 17.04, I enabled systemd-resolved logging. The output
for "affected" domains (ie. ones named in the search path) listed
"LLMNR"; for other domains it listed "LLMNR" and "DNS" strategies. I
will try to reproduce this in the artful VM and will hopefully be able
to post the debugging output tomorrow.

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Title:
  Search list in resolv.conf breaks resolving for that domain

Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  Ubuntu 17.04
  systemd 232-21ubuntu5

  Adding a domain to the search list in /etc/resolv.conf breaks
  resolving for that domain. Not only does the search list not get used
  as expected, but host names in the domain cannot be resolved by
  systemd-resolved at all.

  I just ran into this after upgrading from ubuntu 16.04 to 17.04 which
  enabled systemd-resolved. I have for a long time used resolveconf to
  add a 'search my-domain'-line to my /etc/resolv.conf.

  
  Example of expected behaviour. With Googles DNS server (8.8.8.8) and ubuntu.com in the search list in /etc/resolv.conf. Both dig and systemd-resolve can resolve www.ubuntu.com and www:

      $ cat /etc/resolv.conf 
      nameserver 8.8.8.8
      search ubuntu.com
      $ dig +nostat +nocmd www.ubuntu.com
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55037
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
      
      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 512
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A
      
      ;; ANSWER SECTION:
      www.ubuntu.com.		501	IN	A	91.189.89.115
      
      $ dig +search +nostat +nocmd www
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 25772
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
      
      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 512
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A
      
      ;; ANSWER SECTION:
      www.ubuntu.com.		382	IN	A	91.189.89.103
      
      $ systemd-resolve www.ubuntu.com
      www.ubuntu.com: 91.189.89.115
      
      -- Information acquired via protocol DNS in 2.7ms.
      -- Data is authenticated: no
      $ systemd-resolve www
      www: 91.189.90.59
           (www.ubuntu.com)
      
      -- Information acquired via protocol DNS in 3.8ms.
      -- Data is authenticated: no

  Ubuntu 17.04 default config, with the systemd-resolved name server in
  /etc/resolv.conf and no search list. www.ubuntu.com can still be
  resolved correctly:

      $ cat /etc/resolv.conf
      nameserver 127.0.0.53
      $ dig +nostat +nocmd www.ubuntu.com
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 64646
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
      
      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 65494
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A
      
      ;; ANSWER SECTION:
      www.ubuntu.com.		482	IN	A	91.189.89.110
      $ systemd-resolve www.ubuntu.com
      www.ubuntu.com: 91.189.90.58
      
      -- Information acquired via protocol DNS in 18.2ms.
      -- Data is authenticated: no

  Broken behaviour, using the systemd-resolved name server and specify
  ubuntu.com in search list. Resolving fails for www.ubuntu.com and www,
  both using dig (DNS) and using sytemd-resolve:

      $ cat /etc/resolv.conf
      nameserver 127.0.0.53
      search ubuntu.com
      $ dig +nostat +nocmd www.ubuntu.com
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 33334
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
      
      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 65494
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A
      
      $ dig +search +nostat +nocmd www
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 50588
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
      
      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 65494
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A
      
      $ systemd-resolve www.ubuntu.com
      www.ubuntu.com: resolve call failed: No appropriate name servers or networks for name found
      $ systemd-resolve www
      www: resolve call failed: All attempts to contact name servers or networks failed

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