LUA: Backport CVE-2020-24370's patch

CVE-2020-24370 is a security vulnerability in lua. Although the CVE
description in CVE-2020-24370 said that this CVE only affected lua
5.4.0, according to lua this CVE actually existed since lua 5.2. The
root cause of this CVE is the negation overflow that occurs when you
try to take the negative of 0x80000000. Thus, this CVE also exists in
openzfs. Try to backport the fix to the lua in openzfs since the
original fix is for 5.4 and several functions have been changed.

https://github.com/advisories/GHSA-gfr4-c37g-mm3v
https://nvd.nist.gov/vuln/detail/CVE-2020-24370
https://www.lua.org/bugs.html#5.4.0-11
https://github.com/lua/lua/commit/a585eae6e7ada1ca9271607a4f48dfb1786

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: ChenHao Lu <18302010006@fudan.edu.cn>
Closes #15847

diff --git a/module/lua/ldebug.c b/module/lua/ldebug.c
index 0092474c762d777290f31fc638618066c7d9b488..23e321bb12472d503a63b14a0d00ae42032531ee 100644 (file)
--- a/module/lua/ldebug.c
+++ b/module/lua/ldebug.c
@@ -111,10 +111,11 @@ static const char *upvalname (Proto *p, int uv) {
 
 static const char *findvararg (CallInfo *ci, int n, StkId *pos) {
   int nparams = clLvalue(ci->func)->p->numparams;
-  if (n >= ci->u.l.base - ci->func - nparams)
+  int nvararg = cast_int(ci->u.l.base - ci->func) - nparams;
+  if (n <= -nvararg)
     return NULL;  /* no such vararg */
   else {
-    *pos = ci->func + nparams + n;
+    *pos = ci->func + nparams - n;
     return "(*vararg)";  /* generic name for any vararg */
   }
 }
@@ -126,7 +127,7 @@ static const char *findlocal (lua_State *L, CallInfo *ci, int n,
   StkId base;
   if (isLua(ci)) {
     if (n < 0)  /* access to vararg values? */
-      return findvararg(ci, -n, pos);
+      return findvararg(ci, n, pos);
     else {
       base = ci->u.l.base;
       name = luaF_getlocalname(ci_func(ci)->p, n, currentpc(ci));