system.cpp

/* Copyright (c) 2021, 2022, 2023 Vinícius dos Santos Oliveira

   Distributed under the Boost Software License, Version 1.0. (See accompanying
   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) */

#include <csignal>

#include <boost/preprocessor/control/iif.hpp>
#include <boost/vmd/is_number.hpp>
#include <boost/vmd/empty.hpp>

#define LUA_REGISTRYINDEX	(-10000)

struct lua_State;
typedef long lua_Integer;
typedef int (*lua_CFunction) (lua_State *L);

struct vm_context
{
    bool is_master();
};

void lua_newtable (lua_State *L);
void lua_pushliteral (lua_State *L, const char *s);
void lua_pushlightuserdata (lua_State *L, void *p);
void lua_pushinteger (lua_State *L, lua_Integer n);
void lua_pushcfunction (lua_State *L, lua_CFunction f);
void lua_rawset (lua_State *L, int index);

lua_Integer luaL_checkinteger(lua_State*, int);
int luaL_error (lua_State *L, const char *fmt, ...);

vm_context& get_vm_context(lua_State*);

namespace emilua {

static char system_signal_key;

static int system_signal_raise(lua_State* L)
{
    int signal_number = luaL_checkinteger(L, 1);

#define EMILUA_DETAIL_IS_SIG_X_OR(SIG) signal_number == SIG ||
#define EMILUA_IS_SIG_X_OR(SIG) BOOST_PP_IIF( \
        BOOST_VMD_IS_NUMBER(SIG), EMILUA_DETAIL_IS_SIG_X_OR, BOOST_VMD_EMPTY \
    )(SIG)

#define EMILUA_DETAIL_IS_NOT_SIG_X_AND(SIG) signal_number != SIG &&
#define EMILUA_IS_NOT_SIG_X_AND(SIG) BOOST_PP_IIF( \
        BOOST_VMD_IS_NUMBER(SIG), \
        EMILUA_DETAIL_IS_NOT_SIG_X_AND, BOOST_VMD_EMPTY \
    )(SIG)

    auto& vm_ctx = get_vm_context(L);
    if (!vm_ctx.is_master()) {
        // SIGKILL and SIGSTOP are the only signals that cannot be caught,
        // blocked, or ignored. If we allowed any child VM to raise these
        // signals, then the protection to only allow the main VM to force-exit
        // the process would be moot.
        if (
            EMILUA_IS_SIG_X_OR(SIGKILL)
            EMILUA_IS_SIG_X_OR(SIGSTOP)
            false
        ) {
            return luaL_error(L, "EPERM");
        }

        // Unless the main VM has a handler installed (the check doesn't need to
        // be race-free... that's not a problem) for the process-terminating
        // signal, forbid slave VMs from raising it.
        if (
            // Default action is to continue the process (whatever lol)
            EMILUA_IS_NOT_SIG_X_AND(SIGCONT)

            // Default action is to ignore the signal
            EMILUA_IS_NOT_SIG_X_AND(SIGCHLD)
            EMILUA_IS_NOT_SIG_X_AND(SIGURG)
            EMILUA_IS_NOT_SIG_X_AND(SIGWINCH)

            true
        ) {
            // TODO: a Windows implementation that checks for SIG_DFL
            return luaL_error(L, "EPERM");
        }
    }

#undef EMILUA_IS_NOT_SIG_X_AND
#undef EMILUA_DETAIL_IS_NOT_SIG_X_AND
#undef EMILUA_IS_SIG_X_OR
#undef EMILUA_DETAIL_IS_SIG_X_OR

    int ret = std::raise(signal_number);
    if (ret != 0) {
        return luaL_error(L, "raise error");
    }
    return 0;
}

void init_system(lua_State* L)
{
    lua_pushlightuserdata(L, &system_signal_key);
    {
        lua_newtable(L);

        lua_pushliteral(L, "raise");
        lua_pushcfunction(L, system_signal_raise);
        lua_rawset(L, -3);

#define EMILUA_DEF_SIGNAL(KEY, VALUE) do { \
            lua_pushliteral(L, KEY);       \
            lua_pushinteger(L, VALUE);     \
            lua_rawset(L, -3);             \
        } while(0)
#define EMILUA_DEF_SIGNAL2(SIG) EMILUA_DEF_SIGNAL(#SIG, SIG)

        // <signal.h>
        EMILUA_DEF_SIGNAL2(SIGABRT);
        EMILUA_DEF_SIGNAL2(SIGFPE);
        EMILUA_DEF_SIGNAL2(SIGILL);
        EMILUA_DEF_SIGNAL2(SIGINT);
        EMILUA_DEF_SIGNAL2(SIGSEGV);
        EMILUA_DEF_SIGNAL2(SIGTERM);

#define EMILUA_DEF_SIGNAL3(SIG) BOOST_PP_IIF( \
        BOOST_VMD_IS_NUMBER(SIG), EMILUA_DEF_SIGNAL, BOOST_VMD_EMPTY \
    )(#SIG, SIG)

        // Unix
        EMILUA_DEF_SIGNAL3(SIGALRM);
        EMILUA_DEF_SIGNAL3(SIGBUS);
        EMILUA_DEF_SIGNAL3(SIGCHLD);
        EMILUA_DEF_SIGNAL3(SIGCONT);
        EMILUA_DEF_SIGNAL3(SIGHUP);
        EMILUA_DEF_SIGNAL3(SIGIO);
        EMILUA_DEF_SIGNAL3(SIGKILL);
        EMILUA_DEF_SIGNAL3(SIGPIPE);
        EMILUA_DEF_SIGNAL3(SIGPROF);
        EMILUA_DEF_SIGNAL3(SIGQUIT);
        EMILUA_DEF_SIGNAL3(SIGSTOP);
        EMILUA_DEF_SIGNAL3(SIGSYS);
        EMILUA_DEF_SIGNAL3(SIGTRAP);
        EMILUA_DEF_SIGNAL3(SIGTSTP);
        EMILUA_DEF_SIGNAL3(SIGTTIN);
        EMILUA_DEF_SIGNAL3(SIGTTOU);
        EMILUA_DEF_SIGNAL3(SIGURG);
        EMILUA_DEF_SIGNAL3(SIGUSR1);
        EMILUA_DEF_SIGNAL3(SIGUSR2);
        EMILUA_DEF_SIGNAL3(SIGVTALRM);
        EMILUA_DEF_SIGNAL3(SIGWINCH);
        EMILUA_DEF_SIGNAL3(SIGXCPU);
        EMILUA_DEF_SIGNAL3(SIGXFSZ);

        // Windows
        EMILUA_DEF_SIGNAL3(SIGBREAK);

#undef EMILUA_DEF_SIGNAL3
#undef EMILUA_DEF_SIGNAL2
#undef EMILUA_DEF_SIGNAL
    }
    lua_rawset(L, LUA_REGISTRYINDEX);
}

} // namespace emilua