Fix for CVE-2013-4115

Buffer overflow in the idnsALookup function in dns_internal.cc in Squid
3.2 through 3.2.11 and 3.3 through 3.3.6 allows remote attackers to
cause a denial of service (memory corruption and server termination)
via a long name in a DNS lookup request.

See http://www.squid-cache.org/Advisories/SQUID-2013_2.txt

The patch comes from
http://www.squid-cache.org/Versions/v3/3.1/changesets/squid-3.1-10487.patch

--- squid-3.1.23-orig/src/dns_internal.cc	2013-01-08 18:15:21.000000000 -0800
+++ squid-3.1.23/src/dns_internal.cc	2013-12-10 14:09:08.983526000 -0800
@@ -1532,22 +1532,26 @@
 void
 idnsALookup(const char *name, IDNSCB * callback, void *data)
 {
-    unsigned int i;
-    int nd = 0;
-    idns_query *q;
+    size_t nameLength = strlen(name);
 
-    if (idnsCachedLookup(name, callback, data))
+    // Prevent buffer overflow on q->name
+    if (nameLength > NS_MAXDNAME) {
+        debugs(23, DBG_IMPORTANT, "SECURITY ALERT: DNS name too long to perform lookup: '" << name << "'. see access.log for details.");
+        callback(data, NULL, 0, "Internal error");
         return;
+    }
 
-    q = cbdataAlloc(idns_query);
+    if (idnsCachedLookup(name, callback, data))
+        return;
 
+    idns_query *q = cbdataAlloc(idns_query);
     q->id = idnsQueryID();
-
-    for (i = 0; i < strlen(name); i++)
+    int nd = 0;
+    for (unsigned int i = 0; i < nameLength; ++i)
         if (name[i] == '.')
             nd++;
 
-    if (Config.onoff.res_defnames && npc > 0 && name[strlen(name)-1] != '.') {
+    if (Config.onoff.res_defnames && npc > 0 && name[nameLength-1] != '.') {
         q->do_searchpath = 1;
     } else {
         q->do_searchpath = 0;