Author: Alex Rousskov <rousskov@measurement-factory.com>

Bug 3020: Segmentation fault: nameservers[vc->ns].vc = NULL

Prevent idnsVCClosed segfaults during shutdown or reconfiguration (at least).

idnsShutdown() schedules comm_close and then frees nameservers[] by
calling idnsFreeNameservers. The closing handler tried to access freed
nameservers[]. The patch prevents access to the freed nameservers[]
array in idnsVCClosed and other functions.

TODO: Nameservers[] array management should be rewritten. The array
should not be freed while there are nameservers using it. It should be
freed when the last entry is gone.

  From: 3p1-rock r9583

diff --git a/src/dns_internal.cc b/src/dns_internal.cc
index 1713317394ed0e49a3a4aabd6df01dfed8c7d80c..54a9c6713a26d5e3995e555dfe1a5ba0d374eba2 100644 (file)
--- a/src/dns_internal.cc
+++ b/src/dns_internal.cc
@@ -705,13 +705,15 @@ idnsDoSendQueryVC(nsvc *vc)
 }
 
 static void
-idnsInitVCConnected(int fd, const DnsLookupDetails &, comm_err_t status, int xerrno, void *data)
+idnsInitVCConnected(int fd, const DnsLookupDetails &details, comm_err_t status, int xerrno, void *data)
 {
     nsvc * vc = (nsvc *)data;
 
     if (status != COMM_OK) {
-        char buf[MAX_IPSTRLEN];
-        debugs(78, 1, "idnsInitVCConnected: Failed to connect to nameserver " << nameservers[vc->ns].S.NtoA(buf,MAX_IPSTRLEN) << " using TCP!");
+        char buf[MAX_IPSTRLEN] = "";
+        if (vc->ns < nns)
+            nameservers[vc->ns].S.NtoA(buf,MAX_IPSTRLEN);
+        debugs(78, 1, HERE << "Failed to connect to nameserver " << buf << " using TCP: " << details);
         comm_close(fd);
         return;
     }
@@ -727,7 +729,8 @@ idnsVCClosed(int fd, void *data)
     nsvc * vc = (nsvc *)data;
     delete vc->queue;
     delete vc->msg;
-    nameservers[vc->ns].vc = NULL;
+    if (vc->ns < nns) // XXX: idnsShutdown may have freed nameservers[]
+        nameservers[vc->ns].vc = NULL;
     cbdataFree(vc);
 }
 
@@ -737,6 +740,7 @@ idnsInitVC(int ns)
     char buf[MAX_IPSTRLEN];
 
     nsvc *vc = cbdataAlloc(nsvc);
+    assert(ns < nns);
     nameservers[ns].vc = vc;
     vc->ns = ns;
 
@@ -776,6 +780,7 @@ idnsInitVC(int ns)
 static void
 idnsSendQueryVC(idns_query * q, int ns)
 {
+    assert(ns < nns);
     if (nameservers[ns].vc == NULL)
         idnsInitVC(ns);
 
@@ -1279,6 +1284,7 @@ idnsReadVC(int fd, char *buf, size_t len, comm_err_t flag, int xerrno, void *dat
         return;
     }
 
+    assert(vc->ns < nns);
     debugs(78, 3, "idnsReadVC: FD " << fd << ": received " <<
            (int) vc->msg->contentSize() << " bytes via tcp from " <<
            nameservers[vc->ns].S << ".");
@@ -1462,6 +1468,7 @@ idnsShutdown(void)
         }
     }
 
+    // XXX: vcs are not closed/freed yet and may try to access nameservers[]
     idnsFreeNameservers();
     idnsFreeSearchpath();
 }