lib/util: only close the event_fd in tfork if the caller didn't call tfork_event_fd()

Make closing of the event_fd the global responsibility of the
parent process if it called tfork_event_fd().

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13037

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

2 files changed, 17 insertions, 4 deletions

diff --git a/lib/util/tfork.c b/lib/util/tfork.c
index 71f5e1b6ce9..ca4ab5076ce 100644
--- a/lib/util/tfork.c
+++ b/lib/util/tfork.c
@@ -795,9 +795,14 @@ pid_t tfork_child_pid(const struct tfork *t)
 	return t->worker_pid;
 }
 
-int tfork_event_fd(const struct tfork *t)
+int tfork_event_fd(struct tfork *t)
 {
-	return t->event_fd;
+	int fd = t->event_fd;
+
+	assert(t->event_fd != -1);
+	t->event_fd = -1;
+
+	return fd;
 }
 
 int tfork_status(struct tfork **_t, bool wait)
@@ -857,7 +862,10 @@ int tfork_status(struct tfork **_t, bool wait)
 	} while ((pid == -1) && (errno == EINTR));
 	assert(pid == t->waiter_pid);
 
-	close(t->event_fd);
+	if (t->event_fd != -1) {
+		close(t->event_fd);
+		t->event_fd = -1;
+	}
 
 	free(t);
 	t = NULL;
diff --git a/lib/util/tfork.h b/lib/util/tfork.h
index 1fea2ba4129..89c9f7295a8 100644
--- a/lib/util/tfork.h
+++ b/lib/util/tfork.h
@@ -65,12 +65,17 @@ pid_t tfork_child_pid(const struct tfork *t);
  *
  * @param[in]   t    Pointer to struct tfork returned by tfork_create()
  *
+ * It is the callers responsibility to ensure that the event fd returned by
+ * tfork_event_fd() is closed. By calling tfork_event_fd() ownership of the fd
+ * is transferred to the caller, calling tfork_event_fd() again will trigger an
+ * abort().
+ *
  * @return           An fd that becomes readable when the child created with
  *                   tfork_create() terminates. It is guaranteed that a
  *                   subsequent call to tfork_status() will not block and return
  *                   the exit status of the child.
  **/
-int tfork_event_fd(const struct tfork *t);
+int tfork_event_fd(struct tfork *t);
 
 /**
  * @brief Wait for the child to terminate and return its exit status