Basic protection against Lua os.exit() and posix.exec() (ticket #167)

- Track posix.fork() and only allow exit() and exec() if the script
  has forked. There are other questionable items in posix extensions
  too but these are the worst offenders.
- Using Lua registry for tracking forked status might be more Lua-way
  option but this'll do for now.

2 files changed, 38 insertions, 2 deletions

diff --git a/luaext/lposix.c b/luaext/lposix.c
index 5b26e0c8f..3b251571d 100644
--- a/luaext/lposix.c
+++ b/luaext/lposix.c
@@ -42,6 +42,8 @@
 
 #include "modemuncher.c"
 
+static int have_forked = 0;
+
 static const char *filetype(mode_t m)
 {
 	if (S_ISREG(m))		return "regular";
@@ -323,7 +325,12 @@ static int Pexec(lua_State *L)			/** exec(path,[args]) */
 {
 	const char *path = luaL_checkstring(L, 1);
 	int i,n=lua_gettop(L);
-	char **argv = malloc((n+1)*sizeof(char*));
+	char **argv;
+
+	if (!have_forked)
+	    return luaL_error(L, "exec not permitted in this context");
+
+	argv = malloc((n+1)*sizeof(char*));
 	if (argv==NULL) return luaL_error(L,"not enough memory");
 	argv[0] = (char*)path;
 	for (i=1; i<n; i++) argv[i] = (char*)luaL_checkstring(L, i+1);
@@ -335,7 +342,11 @@ static int Pexec(lua_State *L)			/** exec(path,[args]) */
 
 static int Pfork(lua_State *L)			/** fork() */
 {
-	return pushresult(L, fork(), NULL);
+	pid_t pid = fork();
+	if (pid == 0) {
+	    have_forked = 1;
+	}
+	return pushresult(L, pid, NULL);
 }
 
 
@@ -852,3 +863,27 @@ LUALIB_API int luaopen_posix (lua_State *L)
 	lua_settable(L,-3);
 	return 1;
 }
+
+/* RPM specific overrides for Lua standard library */
+
+static int exit_override(lua_State *L)
+{
+    if (!have_forked)
+	return luaL_error(L, "exit not permitted in this context");
+
+    exit(luaL_optint(L, 1, EXIT_SUCCESS));
+}
+
+static const luaL_reg os_overrides[] =
+{
+    {"exit",    exit_override},
+    {NULL,      NULL}
+};
+
+int luaopen_rpm_os(lua_State *L)
+{
+    lua_pushvalue(L, LUA_GLOBALSINDEX);
+    luaL_openlib(L, "os", os_overrides, 0);
+    return 0;
+}
+
diff --git a/luaext/lposix.h b/luaext/lposix.h
index e1e819cb3..1f9afe980 100644
--- a/luaext/lposix.h
+++ b/luaext/lposix.h
@@ -2,5 +2,6 @@
 #define LPOSIX_H
 
 int luaopen_posix (lua_State *L);
+int luaopen_rpm_os (lua_State *L);
 
 #endif