r22714: Prevent DNS lookup storms when the DNS servers are unreachable.
[samba.git] / source3 / libads / dns.c
index f16cea25554ed0e540e2af1786c5e1c560d74b8c..e0e696c99c97c822be95b0c589982d05f18c595e 100644 (file)
@@ -270,45 +270,76 @@ static int dnssrvcmp( struct dns_rr_srv *a, struct dns_rr_srv *b )
  Simple wrapper for a DNS query
 *********************************************************************/
 
+#define DNS_FAILED_WAITTIME          30
+
 static NTSTATUS dns_send_req( TALLOC_CTX *ctx, const char *name, int q_type, 
                               uint8 **buf, int *resp_length )
 {
        uint8 *buffer = NULL;
        size_t buf_len;
        int resp_len = NS_PACKETSZ;     
-       
+       static time_t last_dns_check = 0;
+       static NTSTATUS last_dns_status = NT_STATUS_OK; 
+       time_t now = time(NULL);
+
+       /* Try to prevent bursts of DNS lookups if the server is down */
+
+       /* Protect against large clock changes */
+
+       if ( last_dns_check > now )
+               last_dns_check = 0;
+
+       /* IF we had a DNS timeout or a bad server and we are still 
+          in the 30 second cache window, just return the previous 
+          status and save the network timeout. */
+
+       if ( (NT_STATUS_EQUAL(last_dns_status,NT_STATUS_IO_TIMEOUT) ||
+             NT_STATUS_EQUAL(last_dns_status,NT_STATUS_CONNECTION_REFUSED)) &&
+            (last_dns_check+DNS_FAILED_WAITTIME) > now ) 
+       {
+               DEBUG(10,("last_dns_check: Returning cached status (%s)\n",
+                         nt_errstr(last_dns_status) ));
+               return last_dns_status;
+       }
+
+       /* Send the Query */
        do {
                if ( buffer )
                        TALLOC_FREE( buffer );
                
                buf_len = resp_len * sizeof(uint8);
 
-               if (buf_len) {
+               if (buf_len) {                  
                        if ( (buffer = TALLOC_ARRAY(ctx, uint8, buf_len)) == NULL ) {
                                DEBUG(0,("ads_dns_lookup_srv: talloc() failed!\n"));
-                               return NT_STATUS_NO_MEMORY;
+                               last_dns_status = NT_STATUS_NO_MEMORY;
+                               last_dns_check = time(NULL);
+                               return last_dns_status; 
                        }
-               } else {
-                       buffer = NULL;
                }
 
                if ( (resp_len = res_query(name, C_IN, q_type, buffer, buf_len)) < 0 ) {
                        DEBUG(3,("ads_dns_lookup_srv: Failed to resolve %s (%s)\n", name, strerror(errno)));
                        TALLOC_FREE( buffer );
+                       last_dns_status = NT_STATUS_UNSUCCESSFUL;
+                       
                        if (errno == ETIMEDOUT) {
-                               return NT_STATUS_IO_TIMEOUT;
+                               last_dns_status = NT_STATUS_IO_TIMEOUT;                         
                        }
                        if (errno == ECONNREFUSED) {
-                               return NT_STATUS_CONNECTION_REFUSED;
+                               last_dns_status = NT_STATUS_CONNECTION_REFUSED;                         
                        }
-                       return NT_STATUS_UNSUCCESSFUL;
+                       last_dns_check = time(NULL);
+                       return last_dns_status;
                }
        } while ( buf_len < resp_len && resp_len < MAX_DNS_PACKET_SIZE );
        
        *buf = buffer;
        *resp_length = resp_len;
 
-       return NT_STATUS_OK;
+       last_dns_check = time(NULL);
+       last_dns_status = NT_STATUS_OK; 
+       return last_dns_status;
 }
 
 /*********************************************************************