agent: Fix detection of exit of scdaemon.

* agent/call-scd.c (start_scd): Acquire START_SCD_LOCK for
SCD_LOCAL_LIST.  Move common case code to fast path.
Release START_SCD_LOCK before calling unlock_scd.
When new CTX is allocated, clear INVALID flag.
(agent_reset_scd): Serialize the access to SCD_LOCAL_LIST by
START_SCD_LOCK.

--

GnuPG-bug-id: 4377
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

agent/call-scd.c

@@ -303,33 +303,19 @@ start_scd (ctrl_t ctrl)
   if (opt.disable_scdaemon)
     return gpg_error (GPG_ERR_NOT_SUPPORTED);
 
-  /* If this is the first call for this session, setup the local data
+  if (ctrl->scd_local && ctrl->scd_local->ctx)
-     structure. */
-  if (!ctrl->scd_local)
     {
-      ctrl->scd_local = xtrycalloc (1, sizeof *ctrl->scd_local);
+      ctrl->scd_local->in_use = 1;
-      if (!ctrl->scd_local)
+      return 0; /* Okay, the context is fine.  */
-        return gpg_error_from_syserror ();
-      ctrl->scd_local->next_local = scd_local_list;
-      scd_local_list = ctrl->scd_local;
     }
 
-  if (ctrl->scd_local->in_use)
+  if (ctrl->scd_local && ctrl->scd_local->in_use)
     {
       log_error ("start_scd: CTX is in use\n");
       return gpg_error (GPG_ERR_INTERNAL);
     }
-  ctrl->scd_local->in_use = 1;
 
-  if (ctrl->scd_local->ctx)
+  /* We need to serialize the access to scd_local_list and primary_scd_ctx. */
-    return 0; /* Okay, the context is fine.  We used to test for an
-                 alive context here and do an disconnect.  Now that we
-                 have a ticker function to check for it, it is easier
-                 not to check here but to let the connection run on an
-                 error instead. */
-
-
-  /* We need to protect the following code. */
   rc = npth_mutex_lock (&start_scd_lock);
   if (rc)
     {
@@ -338,6 +324,25 @@ start_scd (ctrl_t ctrl)
       return gpg_error (GPG_ERR_INTERNAL);
     }
 
+  /* If this is the first call for this session, setup the local data
+     structure. */
+  if (!ctrl->scd_local)
+    {
+      ctrl->scd_local = xtrycalloc (1, sizeof *ctrl->scd_local);
+      if (!ctrl->scd_local)
+	{
+	  err = gpg_error_from_syserror ();
+	  rc = npth_mutex_unlock (&start_scd_lock);
+	  if (rc)
+	    log_error ("failed to release the start_scd lock: %s\n", strerror (rc));
+	  return err;
+	}
+      ctrl->scd_local->next_local = scd_local_list;
+      scd_local_list = ctrl->scd_local;
+    }
+
+  ctrl->scd_local->in_use = 1;
+
   /* Check whether the pipe server has already been started and in
      this case either reuse a lingering pipe connection or establish a
      new socket based one. */
@@ -522,6 +527,10 @@ start_scd (ctrl_t ctrl)
   }
 
  leave:
+  rc = npth_mutex_unlock (&start_scd_lock);
+  if (rc)
+    log_error ("failed to release the start_scd lock: %s\n", strerror (rc));
+
   xfree (abs_homedir);
   if (err)
     {
@@ -531,11 +540,9 @@ start_scd (ctrl_t ctrl)
     }
   else
     {
+      ctrl->scd_local->invalid = 0;
       ctrl->scd_local->ctx = ctx;
     }
-  rc = npth_mutex_unlock (&start_scd_lock);
-  if (rc)
-    log_error ("failed to release the start_scd lock: %s\n", strerror (rc));
   return err;
 }
 
@@ -554,15 +561,21 @@ agent_scd_check_running (void)
    a cleanup of resources used by the current connection. */
 int
 agent_reset_scd (ctrl_t ctrl)
+{
+  int err = npth_mutex_lock (&start_scd_lock);
+
+  if (err)
+    {
+      log_error ("failed to acquire the start_scd lock: %s\n",
+                 strerror (err));
+    }
+  else
     {
       if (ctrl->scd_local)
         {
           if (ctrl->scd_local->ctx)
             {
-          /* We can't disconnect the primary context because libassuan
+              /* We send a reset and keep that connection for reuse. */
-             does a waitpid on it and thus the system would hang.
-             Instead we send a reset and keep that connection for
-             reuse. */
               if (ctrl->scd_local->ctx == primary_scd_ctx)
                 {
                   /* Send a RESTART to the SCD.  This is required for the
@@ -604,6 +617,11 @@ agent_reset_scd (ctrl_t ctrl)
           ctrl->scd_local = NULL;
         }
 
+      err = npth_mutex_unlock (&start_scd_lock);
+      if (err)
+        log_error ("failed to release the start_scd lock: %s\n", strerror (err));
+    }
+
   return 0;
 }