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

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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.
This commit is contained in:
Christopher Faulet 2021-05-03 10:11:13 +02:00
parent 080347fe2a
commit c31b200872
1 changed files with 7 additions and 2 deletions
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9
src/hlua.c
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@ -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);