trace: Emit a warning if tracing is built in

Built in tracing should _not_ be run if it was not set on purpose. Warn as
loud as we can in order to inform the user that they are running a version
with tracing capabilities built in.

This commit also adds a subsys stub because utlimately the logging will happen
in the init phase but because the default log file is not set in the
sys_logging init function, the stub is not useful for now.

Signed-off-by: David Goulet <dgoulet@torproject.org>

5 files changed, 56 insertions, 1 deletions

diff --git a/src/lib/trace/include.am b/src/lib/trace/include.am
index 8440331325..6fe1365652 100644
--- a/src/lib/trace/include.am
+++ b/src/lib/trace/include.am
@@ -26,6 +26,10 @@ if USE_TRACING_INSTRUMENTATION_LTTNG
 include src/lib/trace/lttng/include.am
 endif
 
+if USE_TRACING
 src_lib_libtor_trace_a_SOURCES = $(LIBTOR_TRACE_A_SOURCES)
+else
+src_lib_libtor_trace_a_SOURCES = src/lib/trace/trace_stub.c
+endif
 
 noinst_HEADERS+= $(TRACEHEADERS)
diff --git a/src/lib/trace/trace.h b/src/lib/trace/trace.h
index 94cbbc1e48..22589dbe94 100644
--- a/src/lib/trace/trace.h
+++ b/src/lib/trace/trace.h
@@ -9,7 +9,28 @@
 #ifndef TOR_LIB_TRACE_TRACE_H
 #define TOR_LIB_TRACE_TRACE_H
 
+#include "orconfig.h"
+
 void tor_trace_init(void);
 void tor_trace_free_all(void);
 
+#ifdef HAVE_TRACING
+
+#include "lib/log/log.h"
+
+static inline void
+tracing_log_warning(void)
+{
+  log_warn(LD_GENERAL,
+           "Tracing capabilities have been built in. If this is NOT on "
+           "purpose, your tor is NOT safe to run.");
+}
+
+#else
+
+/* NOP it. */
+#define tracing_log_warning()
+
+#endif /* defined(HAVE_TRACING) */
+
 #endif /* !defined(TOR_LIB_TRACE_TRACE_H) */
diff --git a/src/lib/trace/trace_stub.c b/src/lib/trace/trace_stub.c
new file mode 100644
index 0000000000..9043efe360
--- /dev/null
+++ b/src/lib/trace/trace_stub.c
@@ -0,0 +1,19 @@
+/* Copyright (c) 2020, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file trace_stub.c
+ * \brief Stub declaratinos for use when trace library is disabled.
+ **/
+
+#include "lib/subsys/subsys.h"
+
+#include "lib/trace/trace_sys.h"
+
+const subsys_fns_t sys_tracing = {
+  SUBSYS_DECLARE_LOCATION(),
+
+  .name = "tracing",
+  .supported = false,
+  .level = TRACE_SUBSYS_LEVEL,
+};
diff --git a/src/lib/trace/trace_sys.c b/src/lib/trace/trace_sys.c
index d6e59f4c3d..2ba0258407 100644
--- a/src/lib/trace/trace_sys.c
+++ b/src/lib/trace/trace_sys.c
@@ -25,9 +25,12 @@ subsys_tracing_shutdown(void)
 }
 
 const subsys_fns_t sys_tracing = {
+  SUBSYS_DECLARE_LOCATION(),
+
   .name = "tracing",
   .supported = true,
-  .level = -85,
+  .level = TRACE_SUBSYS_LEVEL,
+
   .initialize = subsys_tracing_initialize,
   .shutdown = subsys_tracing_shutdown,
 };
diff --git a/src/lib/trace/trace_sys.h b/src/lib/trace/trace_sys.h
index e9c97c08fb..d4da5a9701 100644
--- a/src/lib/trace/trace_sys.h
+++ b/src/lib/trace/trace_sys.h
@@ -11,4 +11,12 @@
 
 extern const struct subsys_fns_t sys_tracing;
 
+/**
+ * Subsystem level for the tracing system.
+ *
+ * Defined here so that it can be shared between the real and stub
+ * definitions.
+ **/
+#define TRACE_SUBSYS_LEVEL (-85)
+
 #endif /* !defined(TOR_TRACE_SYS_H) */