svn commit: r318578 - head/usr.sbin/nscd

[Cy Schubert]

Author: cy
Date: Sat May 20 16:58:48 2017
New Revision: 318578
URL: https://svnweb.freebsd.org/changeset/base/318578

Log:
  Fix non-recoverable name resolution failures due to negative cache
  entries never expiring. This patch honours the negative cache timeout.
  
  To test/experience the failure do the following:
  
  1. Edit /etc/ncd.conf to adjust the cache timeouts as follows:
  
  	positive-time-to-live hosts 30
  	negative-time-to-live hosts 1
  
  2. Ensure that nsswitch.conf hosts line contains something like:
  
  	hosts: files cache dns
  
  	Note that cache must be specified before dns.
  
  3. Start nscd.
  
  4. Run the following command:
  
  	while true; do nc -z -w 3 www.google.com 80; sleep 5; done
  
  5. While running the command, remove or comment out all nameserver
     statements in /etc/resolv.conf. After a short while you will notice
     non-recoverable name rsolution failures.
  
  6. Uncomment or replace all nameserver statements back into
     /etc/resolv.conf. Take note that name resolution never recovers.
     To recover nscd must be restarted. This patch fixes this.
  
  PR:		207804
  Submitted by:	Jov <amutu at amutu.com>
  MFC after:	1 week

Modified:
  head/usr.sbin/nscd/query.c

Modified: head/usr.sbin/nscd/query.c
==============================================================================
--- head/usr.sbin/nscd/query.c	Sat May 20 16:47:00 2017	(r318577)
+++ head/usr.sbin/nscd/query.c	Sat May 20 16:58:48 2017	(r318578)
@@ -743,9 +743,14 @@ on_read_request_process(struct query_sta
 				&read_response->data_size);
 
 			if (read_response->error_code == -2) {
-				read_response->error_code = 0;
-				read_response->data = NULL;
-				read_response->data_size = 0;
+				read_response->data = malloc(
+					read_response->data_size);
+				assert(read_response != NULL);
+				read_response->error_code = cache_read(neg_c_entry,
+					read_request->cache_key,
+		    			read_request->cache_key_size,
+		    			read_response->data,
+		    			&read_response->data_size);
 			}
 		}
 		configuration_unlock_entry(qstate->config_entry, CELT_NEGATIVE);