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Bug 1745730

Summary: Unable to query TXT records with one or more subdomains when appending the domain to the short name
Product: Red Hat Enterprise Linux 8 Reporter: Lucas Caparelli <lcaparel>
Component: bindAssignee: Petr Menšík <pemensik>
Status: CLOSED NOTABUG QA Contact: qe-baseos-daemons
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 8.0CC: rhayden
Target Milestone: rcFlags: pm-rhel: mirror+
Target Release: 8.0   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2020-03-18 14:43:50 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Lucas Caparelli 2019-08-26 18:41:31 UTC 
Description of problem:

Unable to query TXT records with one or more subdomains (separate from search domains defined in /etc/resolv.conf) when appending the domain to the short name (for example using the "+search" option with dig or simply by running nslookup).

Querying the FQDN resolves successfully, the issue only surfaces when attempting to resolve via short name.

This issue was initially observed on RHEL 7 after patching bind-utils. As RHEL 7 has entered Maintenance Phase I'm filing the BZ against RHEL 8.

Version-Release number of selected component (if applicable): bind-utils-9.11.4-16.P2.el8.x86_64

How reproducible: easily


Steps to Reproduce:
1. Make sure you have a TXT record with one or more subdomains (apart from the actual zone domain), such as the example below from the "lab.com" zone:

  _test._test        IN      TXT      "HEY, YOU RESOLVED ME WITH A SUBDOMAIN"

2. Make sure /etc/resolv.conf has the correct search domain configured:

  search lab.com

3. Query the record while attempting to append the search domain. Example:

  $ dig TXT +search _test._test 

Actual results:

[root@localhost ~]# dig +search TXT _test._test

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-16.P2.el8 <<>> +search TXT _test._test
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 2149
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 0c4043a29fe88f8bf9baaee15d642624a6b53d929486eeeb (good)
;; QUESTION SECTION:
;_test._test.			IN	TXT

;; AUTHORITY SECTION:
.			10555	IN	SOA	a.root-servers.net. nstld.verisign-grs.com. 2019082601 1800 900 604800 86400

;; Query time: 1 msec
;; SERVER: 192.168.121.83#53(192.168.121.83)
;; WHEN: Mon Aug 26 14:34:12 EDT 2019
;; MSG SIZE  rcvd: 143

;; Query time: 1 msec
;; SERVER: 192.168.121.83#53(192.168.121.83)
;; WHEN: Mon Aug 26 14:34:12 EDT 2019
;; MSG SIZE  rcvd: 143


Expected results:

The search domain is appended and the query gets resolved.

Additional info:

Please see below results from testing on RHEL 7. It's possible to see the query actually got resolved as expected on an older version of bind-utils:

---------------------------------------------------------------------
[root@localhost ~]# cat /etc/resolv.conf
# Generated by NetworkManager
search lab.com
nameserver 192.168.121.83
[root@localhost ~]# rpm -q bind-utils 
bind-utils-9.9.4-73.el7_6.x86_64
[root@localhost ~]# dig +search TXT _test

; <<>> DiG 9.9.4-RedHat-9.9.4-73.el7_6 <<>> +search TXT _test
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 33544
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;_test.lab.com.			IN	TXT

;; ANSWER SECTION:
_test.lab.com.		86400	IN	TXT	"HEY, YOU RESOLVED ME"

;; AUTHORITY SECTION:
lab.com.		86400	IN	NS	ns.lab.com.

;; ADDITIONAL SECTION:
ns.lab.com.		86400	IN	A	192.168.121.83

;; Query time: 1 msec
;; SERVER: 192.168.121.83#53(192.168.121.83)
;; WHEN: Qui Ago 22 16:23:45 EDT 2019
;; MSG SIZE  rcvd: 108

[root@localhost ~]# dig +search TXT _test._test
;; Query time: 0 msec
;; SERVER: 192.168.121.83#53(192.168.121.83)
;; WHEN: Qui Ago 22 16:23:59 EDT 2019
;; MSG SIZE  rcvd: 40


; <<>> DiG 9.9.4-RedHat-9.9.4-73.el7_6 <<>> +search TXT _test._test
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41145
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;_test._test.lab.com.		IN	TXT

;; ANSWER SECTION:
_test._test.lab.com.	86400	IN	TXT	"HEY, YOU RESOLVED ME WITH A SUBDOMAIN"

;; AUTHORITY SECTION:
lab.com.		86400	IN	NS	ns.lab.com.

;; ADDITIONAL SECTION:
ns.lab.com.		86400	IN	A	192.168.121.83

;; Query time: 1 msec
;; SERVER: 192.168.121.83#53(192.168.121.83)
;; WHEN: Qui Ago 22 16:23:59 EDT 2019
;; MSG SIZE  rcvd: 131

[root@localhost ~]# yum update bind-utils -y
(output omitted)
[root@localhost ~]# rpm -q bind-utils
bind-utils-9.11.4-9.P2.el7.x86_64
[root@localhost ~]# dig +search TXT _test

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>> +search TXT _test
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42989
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;_test.lab.com.			IN	TXT

;; ANSWER SECTION:
_test.lab.com.		86400	IN	TXT	"HEY, YOU RESOLVED ME"

;; AUTHORITY SECTION:
lab.com.		86400	IN	NS	ns.lab.com.

;; ADDITIONAL SECTION:
ns.lab.com.		86400	IN	A	192.168.121.83

;; Query time: 0 msec
;; SERVER: 192.168.121.83#53(192.168.121.83)
;; WHEN: Qui Ago 22 16:39:16 EDT 2019
;; MSG SIZE  rcvd: 108

[root@localhost ~]#  dig +search TXT _test._test

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>> +search TXT _test._test
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 42397
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;_test._test.			IN	TXT

;; Query time: 4 msec
;; SERVER: 192.168.121.83#53(192.168.121.83)
;; WHEN: Qui Ago 22 16:39:36 EDT 2019
;; MSG SIZE  rcvd: 40

---------------------------------------------------------------------

Strangely, the response code is SERVFAIL instead of the NXDOMAIN observed on RHEL 8 as client.
Comment 1 rhayden 2019-08-28 16:18:43 UTC 
Potentially related bug at https://bugzilla.redhat.com/show_bug.cgi?id=1743572

Discussion on using the "options ndots:3" in /etc/resolv.conf to relax the security stance.
Comment 2 Lucas Caparelli 2019-08-28 16:42:27 UTC 
(In reply to rhayden from comment #1)
> Potentially related bug at
> https://bugzilla.redhat.com/show_bug.cgi?id=1743572
> 
> Discussion on using the "options ndots:3" in /etc/resolv.conf to relax the
> security stance.

That works here too. 

I assumed the issue was exclusive to TXT records due to how the issue was observed on the customer's environment, sorry about that. I just tested for an A record and I see the same behavior (the ndots workaround is also good then).

It seems this bug may be actually a duplicate then.
Comment 3 Petr Menšík 2020-03-18 14:43:50 UTC 
Would close it as a duplicate. However, this issue would be fixed in RHEL 7, since it originally worked there. But such thing never worked in RHEL 8.

We currently do not have plan to fix it in RHEL8, since upstream considers it a bad habbit to include dots in search directive queries. Search was supposed to search bare name without a dot in current set of domains. It would work well with www or ftp, but not www.subdomain or ldap.division.

General recommendation is to use full absolute anywhere and not to rely on search or domain directives in /etc/resolv.conf. They might be reconfigured by DHCP, which is not secured in any way. Full domains are safer in this mode, because it either resolves or fails. It is not passed to every search domain first or as a final try. We would like to keep it so.

It it is important feature you cannot overcome, feel free to reopen the bug. But please explain how you use it and why full name is not possible to use.

Until that, closing as not a bug.