dnsdist: Lock the Lua context before executing a LuaAction

Otherwise the stack of the Lua context might get corrupted
whenever another Lua function (blockfilter, policy, maintenance or
another LuaAction) is simultaneously called from another thread.

We might be able to use a separate execution stack via
createThread()/lua_newthread(), but if I understand correctly how
it works, we would need to be sure that the Lua function called
does not access the global state at all, which is probably too
restrictive.

This should fix #3374, #3375, #3376, #3377, #3378, #3379, #3383,
and hopefully the random travis failures in our regression tests.

diff --git a/pdns/dnsdist-lua.cc b/pdns/dnsdist-lua.cc
index d83f5866474ff7053e47c7643eb1ff415fc0d6c8..32fc8328216f99660b384d2de2b3cda467c8b141 100644 (file)
--- a/pdns/dnsdist-lua.cc
+++ b/pdns/dnsdist-lua.cc
@@ -22,6 +22,7 @@ public:
 
   Action operator()(DNSQuestion* dq, string* ruleresult) const override
   {
+    std::lock_guard<std::mutex> lock(g_luamutex);
     auto ret = d_func(dq);
     if(ruleresult)
       *ruleresult=std::get<1>(ret);