Merge pull request #797 from pi-hole/fix/reacquire_client_pointer_aft…

…er_resolve

Reacquire client and upstream pointers after a name resolution

src/resolve.c

@@ -303,17 +303,17 @@ void resolveClients(const bool onlynew)
  int skipped = 0;
  for(int clientID = 0; clientID < clientscount; clientID++)
  {
- // Get client pointer
+ // Memory access needs to get locked
+ lock_shm();
+ // Get client pointer for the first time (reading data)
  clientsData* client = getClient(clientID, true);
  if(client == NULL)
  {
- logg("ERROR: Unable to get client pointer with ID %i, skipping...", clientID);
+ logg("ERROR: Unable to get client pointer (1) with ID %i, skipping...", clientID);
  skipped++;
  continue;
  }
 
- // Memory access needs to get locked
- lock_shm();
  bool newflag = client->new;
  size_t ippos = client->ippos;
  size_t oldnamepos = client->namepos;
@@ -331,6 +331,18 @@ void resolveClients(const bool onlynew)
  size_t newnamepos = resolveAndAddHostname(ippos, oldnamepos);
 
  lock_shm();
+ // Get client pointer for the second time (writing data)
+ // We cannot use the same pointer again as we released
+ // the lock in between so we cannot know if something
+ // happened to the shared memory object (resize event)
+ client = getClient(clientID, true);
+ if(client == NULL)
+ {
+ logg("ERROR: Unable to get client pointer (2) with ID %i, skipping...", clientID);
+ skipped++;
+ continue;
+ }
+
  // Store obtained host name (may be unchanged)
  client->namepos = newnamepos;
  // Mark entry as not new
@@ -356,7 +368,9 @@ void resolveForwardDestinations(const bool onlynew)
  int skipped = 0;
  for(int upstreamID = 0; upstreamID < upstreams; upstreamID++)
  {
- // Get upstream pointer
+ // Memory access needs to get locked
+ lock_shm();
+ // Get upstream pointer for the first time (reading data)
  upstreamsData* upstream = getUpstream(upstreamID, true);
  if(upstream == NULL)
  {
@@ -365,8 +379,6 @@ void resolveForwardDestinations(const bool onlynew)
  continue;
  }
 
- // Memory access needs to get locked
- lock_shm();
  bool newflag = upstream->new;
  size_t ippos = upstream->ippos;
  size_t oldnamepos = upstream->namepos;
@@ -384,6 +396,18 @@ void resolveForwardDestinations(const bool onlynew)
  size_t newnamepos = resolveAndAddHostname(ippos, oldnamepos);
 
  lock_shm();
+ // Get upstream pointer for the second time (writing data)
+ // We cannot use the same pointer again as we released
+ // the lock in between so we cannot know if something
+ // happened to the shared memory object (resize event)
+ upstream = getUpstream(upstreamID, true);
+ if(upstream == NULL)
+ {
+ logg("ERROR: Unable to get upstream pointer with ID %i, skipping...", upstreamID);
+ skipped++;
+ continue;
+ }
+
  // Store obtained host name (may be unchanged)
  upstream->namepos = newnamepos;
  // Mark entry as not new