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[Bug 1818527] Re: Stub resolver cache is corrupted

To: group.of.nepali.translators@xxxxxxxxxxxxxxxxxxx
From: Heitor Alves de Siqueira <1818527@xxxxxxxxxxxxxxxxxx>
Date: Wed, 05 Jun 2019 13:50:29 -0000
Reply-to: Bug 1818527 <1818527@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx
** Description changed:

+ [Impact]
+ systemd-resolved fails to resolve A records
+ 
+ [Description]
+ When systemd-resolve caches a non-existent CNAME record for a specific domain, further attempts at resolving A records for that same domain  fail. This has been fixed upstream in v240.
+ 
+ Upstream commit: https://github.com/systemd/systemd/commit/3740146a4cbd
+ 
+ $ git describe --contains 3740146a4cbd
+ v240~839
+ 
+ $ rmadison systemd --arch amd64
+  systemd | 229-4ubuntu4     | xenial          | source, ...
+  systemd | 229-4ubuntu21.21 | xenial-security | source, ...
+  systemd | 229-4ubuntu21.21 | xenial-updates  | source, ...
+  systemd | 237-3ubuntu10    | bionic          | source, ...
+  systemd | 237-3ubuntu10.19 | bionic-security | source, ...
+  systemd | 237-3ubuntu10.21 | bionic-updates  | source, ...
+  systemd | 237-3ubuntu10.22 | bionic-proposed | source, ...
+  systemd | 239-7ubuntu10    | cosmic          | source, ...
+  systemd | 239-7ubuntu10.12 | cosmic-security | source, ...
+  systemd | 239-7ubuntu10.13 | cosmic-updates  | source, ...
+  systemd | 239-7ubuntu10.14 | cosmic-proposed | source, ...
+  systemd | 240-6ubuntu5     | disco           | source, ...
+  systemd | 240-6ubuntu5.1   | disco-proposed  | source, ...
+  systemd | 240-6ubuntu9     | eoan            | source, ...
+ 
+ Despite the package versions above, only Bionic is affected. Cosmic
+ already includes a backported fix, and Xenial doesn't seem affected due
+ to resolvconf handling DNS resolution.
+ 
+ [Test Case]
+ Flush resolved's caches and try resolving a non-existent CNAME record. Further resolution attempts for the corresponding A record will fail:
+ 
+ $ systemd-resolve --flush-caches
+ $ dig github.com CNAME
+ $ dig github.com A
+ 
+ [Regression Potential]
+ The regression potential for this fix should be very low, as it's a direct cherry-pick from upstream systemd. It has seen extensive testing  in both upstream and other Ubuntu releases, and was verified for Bionic through autopkgtests.
+ 
+ ================================
+ 
+ [Original Description]
+ 
  It seems that when systemd-resolve cache an non-existent CNAME record
  for a domain, any attempt to resolve A record for the same domain fail.
  
  systemd version the issue has been seen with
  Installed: 237-3ubuntu10.13
  Used distribution
  
  Distributor ID: Ubuntu
  Description: Ubuntu 18.04.2 LTS
  Release: 18.04
  Codename: bionic
  
  Expected behaviour you didn't see
  
  Return A record for a domain when it exists.
  
  Unexpected behaviour you saw
  
  Resolution failed.
  
  Steps to reproduce the problem
  
  Whait for 1 minutes (github.com TTL for A record)
  
  Try to resolv github.com CNAME record dig CNAME github.com
  
  This will return an empty result.
  
  Then try to resolve github.com A record dig A github.com.
  
  This will now return empty result unless you restart systemd-resolved or
  wait for cache expiration.
  
  At the same time using another DNS will resolve correctly dig A
  github.com @8.8.8.8.
  
  Exemple :
  
  Wait for 1 minutes to let cache expire, then run
  
  dig CNAME github.com
  dig A github.com
  # no result
  dig A github.com @8.8.8.8
  # ;; ANSWER SECTION:
  # github.com.		59	IN	A	192.30.253.113
  # github.com.		59	IN	A	192.30.253.112
  
  PS: Don't forget to restart systemd-resolve, before trying to post an
  answer.
  
  This bug was first reported in github
  https://github.com/systemd/systemd/issues/11789 but systemd version in
  ubuntu is too  old.

** Changed in: systemd (Ubuntu Xenial)
       Status: New => Invalid

** Changed in: systemd (Ubuntu Xenial)
   Importance: Medium => Undecided

** Changed in: systemd (Ubuntu Xenial)
     Assignee: Heitor Alves de Siqueira (halves) => (unassigned)

** Changed in: systemd (Ubuntu Bionic)
       Status: Confirmed => In Progress

** Patch added: "lp1818527-bionic.debdiff"
   https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1818527/+attachment/5268921/+files/lp1818527-bionic.debdiff

** Tags added: sts sts-sponsor

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https://bugs.launchpad.net/bugs/1818527

Title:
  Stub resolver cache is corrupted

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Xenial:
  Invalid
Status in systemd source package in Bionic:
  In Progress

Bug description:
  [Impact]
  systemd-resolved fails to resolve A records

  [Description]
  When systemd-resolve caches a non-existent CNAME record for a specific domain, further attempts at resolving A records for that same domain  fail. This has been fixed upstream in v240.

  Upstream commit:
  https://github.com/systemd/systemd/commit/3740146a4cbd

  $ git describe --contains 3740146a4cbd
  v240~839

  $ rmadison systemd --arch amd64
   systemd | 229-4ubuntu4     | xenial          | source, ...
   systemd | 229-4ubuntu21.21 | xenial-security | source, ...
   systemd | 229-4ubuntu21.21 | xenial-updates  | source, ...
   systemd | 237-3ubuntu10    | bionic          | source, ...
   systemd | 237-3ubuntu10.19 | bionic-security | source, ...
   systemd | 237-3ubuntu10.21 | bionic-updates  | source, ...
   systemd | 237-3ubuntu10.22 | bionic-proposed | source, ...
   systemd | 239-7ubuntu10    | cosmic          | source, ...
   systemd | 239-7ubuntu10.12 | cosmic-security | source, ...
   systemd | 239-7ubuntu10.13 | cosmic-updates  | source, ...
   systemd | 239-7ubuntu10.14 | cosmic-proposed | source, ...
   systemd | 240-6ubuntu5     | disco           | source, ...
   systemd | 240-6ubuntu5.1   | disco-proposed  | source, ...
   systemd | 240-6ubuntu9     | eoan            | source, ...

  Despite the package versions above, only Bionic is affected. Cosmic
  already includes a backported fix, and Xenial doesn't seem affected
  due  to resolvconf handling DNS resolution.

  [Test Case]
  Flush resolved's caches and try resolving a non-existent CNAME record. Further resolution attempts for the corresponding A record will fail:

  $ systemd-resolve --flush-caches
  $ dig github.com CNAME
  $ dig github.com A

  [Regression Potential]
  The regression potential for this fix should be very low, as it's a direct cherry-pick from upstream systemd. It has seen extensive testing  in both upstream and other Ubuntu releases, and was verified for Bionic through autopkgtests.

  ================================

  [Original Description]

  It seems that when systemd-resolve cache an non-existent CNAME record
  for a domain, any attempt to resolve A record for the same domain
  fail.

  systemd version the issue has been seen with
  Installed: 237-3ubuntu10.13
  Used distribution

  Distributor ID: Ubuntu
  Description: Ubuntu 18.04.2 LTS
  Release: 18.04
  Codename: bionic

  Expected behaviour you didn't see

  Return A record for a domain when it exists.

  Unexpected behaviour you saw

  Resolution failed.

  Steps to reproduce the problem

  Whait for 1 minutes (github.com TTL for A record)

  Try to resolv github.com CNAME record dig CNAME github.com

  This will return an empty result.

  Then try to resolve github.com A record dig A github.com.

  This will now return empty result unless you restart systemd-resolved
  or wait for cache expiration.

  At the same time using another DNS will resolve correctly dig A
  github.com @8.8.8.8.

  Exemple :

  Wait for 1 minutes to let cache expire, then run

  dig CNAME github.com
  dig A github.com
  # no result
  dig A github.com @8.8.8.8
  # ;; ANSWER SECTION:
  # github.com.		59	IN	A	192.30.253.113
  # github.com.		59	IN	A	192.30.253.112

  PS: Don't forget to restart systemd-resolve, before trying to post an
  answer.

  This bug was first reported in github
  https://github.com/systemd/systemd/issues/11789 but systemd version in
  ubuntu is too  old.

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