MB-35993: Add synchronization to auditHandle

The audit daemon handle (auditHandle) does not have any
synchronization around it, resulting in TSan warnings during shutdown
as the Audit object may have been deleted:

ThreadSanitizer: data race

  Write of size 8 at 0x0000009b0130 by main thread:
    #0 std::swap(cb::audit::Audit*&, cb::audit::Audit*&) /usr/local/include/c++/7.3.0/bits/move.h:199 (memcached+0x0000004f335a)
    #1 std::unique_ptr >::reset(cb::audit::Audit*) /usr/local/include/c++/7.3.0/bits/unique_ptr.h:374 (memcached+0x0000004f335a)
    #2 shutdown_audit() kv_engine/daemon/mcaudit.cc:348 (memcached+0x0000004f335a)
    #3 memcached_main kv_engine/daemon/memcached.cc:2503 (memcached+0x000000435a46)
    #4 main kv_engine/daemon/main.cc:33 (memcached+0x00000042145e)

  Previous read of size 8 at 0x0000009b0130 by thread T8 (mutexes: write M1049192993527234104):
    #0 std::__uniq_ptr_impl >::_M_ptr() const /usr/local/include/c++/7.3.0/bits/unique_ptr.h:147 (memcached+0x0000004f3433)
    #1 std::unique_ptr >::get() const /usr/local/include/c++/7.3.0/bits/unique_ptr.h:337 (memcached+0x0000004f3433)
    #2 std::unique_ptr >::operator->() const /usr/local/include/c++/7.3.0/bits/unique_ptr.h:331 (memcached+0x0000004f3433)
    #3 stats_audit(std::function)> const&, Cookie&) kv_engine/daemon/mcaudit.cc:361 (memcached+0x0000004f3433)
    #4 stat_audit_executor kv_engine/daemon/protocol/mcbp/stats_context.cc:446 (memcached+0x000000528f72)

  Location is global 'auditHandle' of size 8 at 0x0000009b0130 (memcached+0x0000009b0130)

Fix by using folly::Synchronized<> for the auditHandle. Note that
exclusive access is only needed during initialization & shutdown, so
there should be no additional contention for actually adding audit
events (where shared access is sufficient).

Change-Id: I34966f08674c6363fde4592b5c4bede48747fb2f
Reviewed-on: http://review.couchbase.org/114945
Tested-by: Build Bot <[email protected]>
Reviewed-by: Richard de Mellow <[email protected]>
Reviewed-by: Trond Norbye <[email protected]>

daemon/mcaudit.cc

@@ -32,11 +32,12 @@
 #include <memcached/isotime.h>
 #include <platform/string_hex.h>
 
+#include <folly/Synchronized.h>
 #include <nlohmann/json.hpp>
 
 #include <sstream>
 
-static cb::audit::UniqueAuditPtr auditHandle;
+static folly::Synchronized<cb::audit::UniqueAuditPtr> auditHandle;
 
 static std::atomic_bool audit_enabled{false};
 
@@ -113,9 +114,13 @@ static void do_audit(uint32_t id,
                      const nlohmann::json& event,
                      const char* warn) {
     auto text = event.dump();
-    if (!auditHandle->put_event(id, text)) {
-        LOG_WARNING("{}: {}", warn, text);
-    }
+    auditHandle.withRLock([id, warn, &text](auto& handle) {
+        if (handle) {
+            if (!handle->put_event(id, text)) {
+                LOG_WARNING("{}: {}", warn, text);
+            }
+        }
+    });
 }
 
 void audit_auth_failure(const Connection& c, const char* reason) {
@@ -263,7 +268,12 @@ bool mc_audit_event(uint32_t audit_eventid, cb::const_byte_buffer payload) {
 
     cb::const_char_buffer buffer{reinterpret_cast<const char*>(payload.data()),
                                  payload.size()};
-    return auditHandle->put_event(audit_eventid, buffer);
+    return auditHandle.withRLock([audit_eventid, buffer](auto& handle) {
+        if (!handle) {
+            return false;
+        }
+        return handle->put_event(audit_eventid, buffer);
+    });
 }
 
 namespace cb {
@@ -335,28 +345,37 @@ static void event_state_listener(uint32_t id, bool enabled) {
 
 void initialize_audit() {
     /* Start the audit daemon */
-    auditHandle = cb::audit::create_audit_daemon(
+    auto audit = cb::audit::create_audit_daemon(
             Settings::instance().getAuditFile(), get_server_api()->cookie);
-    if (!auditHandle) {
+    if (!audit) {
         FATAL_ERROR(EXIT_FAILURE, "FATAL: Failed to start audit daemon");
     }
-    auditHandle->add_event_state_listener(event_state_listener);
-    auditHandle->notify_all_event_states();
+    audit->add_event_state_listener(event_state_listener);
+    audit->notify_all_event_states();
+    *auditHandle.wlock() = std::move(audit);
 }
 
 void shutdown_audit() {
-    auditHandle.reset();
+    auditHandle.wlock()->reset();
 }
 
 ENGINE_ERROR_CODE reconfigure_audit(Cookie& cookie) {
-    if (auditHandle->configure_auditdaemon(Settings::instance().getAuditFile(),
-                                           static_cast<void*>(&cookie))) {
-        return ENGINE_EWOULDBLOCK;
-    }
-
-    return ENGINE_FAILED;
+    return auditHandle.withRLock([&cookie](auto& handle) {
+        if (!handle) {
+            return ENGINE_FAILED;
+        }
+        if (handle->configure_auditdaemon(Settings::instance().getAuditFile(),
+                                          static_cast<void*>(&cookie))) {
+            return ENGINE_EWOULDBLOCK;
+        }
+        return ENGINE_FAILED;
+    });
 }
 
 void stats_audit(const AddStatFn& add_stats, Cookie& cookie) {
-    auditHandle->stats(add_stats, &cookie);
+    auditHandle.withRLock([&add_stats, &cookie](auto& handle) {
+        if (handle) {
+            handle->stats(add_stats, &cookie);
+        }
+    });
 }