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Bug 656014

Summary: nscd host caching does not respect DNS TTLs
Product: Red Hat Enterprise Linux 6 Reporter: Matt Savona <matt.savona>
Component: glibcAssignee: Andreas Schwab <schwab>
Status: CLOSED ERRATA QA Contact: qe-baseos-tools-bugs
Severity: medium Docs Contact:
Priority: low    
Version: 6.0CC: bugzilla, fweimer, juanino, mfranc, mrkfact, pmuller
Target Milestone: rc   
Target Release: ---   
Hardware: x86_64   
OS: Unspecified   
Whiteboard:
Fixed In Version: glibc-2.12-1.15.el6 Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
: 929035 (view as bug list) Environment:
Last Closed: 2011-05-19 13:16:13 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 929035, 962903    
Attachments:
Description Flags
nscd.log - debug 9 none

Description Matt Savona 2010-11-22 21:07:58 UTC 
Description of problem:
---------------------------------------------------------------------
When nscd is enabled and a lookup is performed for a DNS record with a TTL of 0, nscd proceeds to cache the result when it should not. This behavior is seen via lookups initiated by getaddrinfo when it should not.

Version-Release number of selected component (if applicable):
---------------------------------------------------------------------
Tested against RHEL5 and RHEL6, up to versions:
glibc-2.12-1.7.el6.x86_64
nscd-2.12-1.7.el6.x86_64

How reproducible:
---------------------------------------------------------------------
100%

Steps to Reproduce (hostnames and IPs masked):
---------------------------------------------------------------------

# DNS RECORD IS:
;; ANSWER SECTION:
nfs.appliance.company.com. 0     IN      A       1.1.1.55

(where the returned IP may vary based on specific conditions determined by the NFS appliance)

# WITH NSCD ENABLED:
/etc/init.d/nscd start
/etc/init.d/nscd reload
ltrace -f getent ahosts nfs.appliance.company.com 2>&1 | egrep "getaddrinfo|STREAM" | grep -v printf
getaddrinfo("nfs.appliance.company.com", NULL, 0x7fff65794a90, 0x7fff65794b08) = 0
1.1.1.56    STREAM nfs.appliance.company.com
# [ run this as many times as you want, same result ]

# WITH NSCD DISABLED:
/etc/init.d/nscd stop
ltrace -f getent ahosts nfs.appliance.company.com 2>&1 | egrep "getaddrinfo|STREAM" | grep -v printf
getaddrinfo("nfs.appliance.company.com", NULL, 0x7ffff521eb80, 0x7ffff521ebf8) = 0
1.1.1.56    STREAM nfs.appliance.company.com
ltrace -f getent ahosts nfs.appliance.company.com 2>&1 | egrep "getaddrinfo|STREAM" | grep -v printf
getaddrinfo("nfs.appliance.company.com", NULL, 0x7fffb80836b0, 0x7fffb8083728) = 0
1.1.1.53    STREAM nfs.appliance.company.com
ltrace -f getent ahosts nfs.appliance.company.com 2>&1 | egrep "getaddrinfo|STREAM" | grep -v printf
getaddrinfo("nfs.appliance.company.com", NULL, 0x7fff9d6aa5e0, 0x7fff9d6aa658) = 0
1.1.1.57    STREAM nfs.appliance.company.com
# [ run this as many times as you want, different results ]
  
Expected results:
---------------------------------------------------------------------
For DNS records with a TTL of 0, the results with NSCD enabled should be identical to the results seen with NSCD disabled.

Additional info:
---------------------------------------------------------------------

References regarding expected nscd and getaddrinfo behavior here:
http://udrepper.livejournal.com/16362.html
http://sourceware.org/bugzilla/show_bug.cgi?id=4428
Comment 2 Andreas Schwab 2010-11-23 10:38:12 UTC 
Please enable full debug level and attach the nscd log.
Comment 3 Matt Savona 2010-11-23 13:12:26 UTC 
Created attachment 462322 [details]
nscd.log - debug 9
Comment 5 Matt Savona 2011-01-13 15:11:57 UTC 
Will the fix referenced here in glibc-2.12-1.15.el6 for RHEL6 be backported for RHEL5 as well?
Comment 8 errata-xmlrpc 2011-05-19 13:16:13 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHBA-2011-0584.html