BUG/MINOR: hlua: Don't rely on top of the stack when using Lua buffers

When the lua buffers are used, a variable number of stack slots may be
used. Thus we cannot assume that we know where the top of the stack is. It
was not an issue for lua < 5.4.3 (at least for small buffers). But
'socket:receive()' now fails with lua 5.4.3 because a light userdata is
systematically pushed on the top of the stack when a buffer is initialized.

To fix the bug, in hlua_socket_receive(), we save the index of the top of
the stack before creating the buffer. This way, we can check the number of
arguments, regardless anything was pushed on the stack or not.

Note that the other buffer usages seem to be safe.

This patch should solve the issue #1240. It should be backport to all stable
branches.

diff --git a/src/hlua.c b/src/hlua.c
index e947370a94f5b3734d363e018ab31da7749c2c8b..2a6528f613982fc4964a9c37a50e2fa8873e11a5 100644 (file)
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -2130,7 +2130,7 @@ __LJMP static int hlua_socket_receive(struct lua_State *L)
 {
        int wanted = HLSR_READ_LINE;
        const char *pattern;
-       int type;
+       int lastarg, type;
        char *error;
        size_t len;
        struct hlua_socket *socket;
@@ -2175,11 +2175,16 @@ __LJMP static int hlua_socket_receive(struct lua_State *L)
        if (lua_gettop(L) != 2)
                lua_replace(L, 2);
 
+       /* Save index of the top of the stack because since buffers are used, it
+        * may change
+        */
+       lastarg = lua_gettop(L);
+
        /* init buffer, and fill it with prefix. */
        luaL_buffinit(L, &socket->b);
 
        /* Check prefix. */
-       if (lua_gettop(L) >= 3) {
+       if (lastarg >= 3) {
                if (lua_type(L, 3) != LUA_TSTRING)
                        WILL_LJMP(luaL_error(L, "Expect a 'string' for the prefix"));
                pattern = lua_tolstring(L, 3, &len);