From 9a9c7f2b7c63a9db203084a3485988c07f17b86c Mon Sep 17 00:00:00 2001
From: William Wilgus <me.theuser@yahoo.com>
Date: Mon, 5 Feb 2018 07:28:08 +0100
Subject: Fix lua failure to catch divide by zero and NaN exceptions

I can only assume in the course of the original conversion to fixed point
math in RbLua the fact that division by zero and NaN handling was to be
caught as a graceful exception by the floating point handler was overlooked.

As a result lua doesn't handle these exceptions and instead results in a
panic on the device.

This patch fixes this handling in the lexer for compile time Inf and Nan
results and in the luavm for runtime division by zero (Inf)

I missed the runtime exception of n%0 added checks for that as well..

Change-Id: I7746c087ea93678e5875f15ec6fe3f29f26bdb31
---
 apps/plugins/lua/lcode.c | 13 ++++++++-----
 apps/plugins/lua/lvm.c   | 28 +++++++++++++++++++++++++---
 2 files changed, 33 insertions(+), 8 deletions(-)

(limited to 'apps/plugins/lua')

diff --git a/apps/plugins/lua/lcode.c b/apps/plugins/lua/lcode.c
index cff626b7fa..cc26ac7521 100644
--- a/apps/plugins/lua/lcode.c
+++ b/apps/plugins/lua/lcode.c
@@ -642,26 +642,27 @@ static int constfolding (OpCode op, expdesc *e1, expdesc *e2) {
     case OP_SUB: r = luai_numsub(v1, v2); break;
     case OP_MUL: r = luai_nummul(v1, v2); break;
     case OP_DIV:
-      if (v2 == 0) return 0;  /* do not attempt to divide by 0 */
+      if (v2 == 0) return -1;  /* do not attempt to divide by 0 */
       r = luai_numdiv(v1, v2); break;
     case OP_MOD:
-      if (v2 == 0) return 0;  /* do not attempt to divide by 0 */
+      if (v2 == 0) return -1;  /* do not attempt to divide by 0 */
       r = luai_nummod(v1, v2); break;
     case OP_POW: r = luai_numpow(v1, v2); break;
     case OP_UNM: r = luai_numunm(v1); break;
     case OP_LEN: return 0;  /* no constant folding for 'len' */
     default: lua_assert(0); r = 0; break;
   }
-  if (luai_numisnan(r)) return 0;  /* do not attempt to produce NaN */
+  if (luai_numisnan(r)) return -2;  /* do not attempt to produce NaN */
   e1->u.nval = r;
   return 1;
 }
 
 
 static void codearith (FuncState *fs, OpCode op, expdesc *e1, expdesc *e2) {
-  if (constfolding(op, e1, e2))
+  int resf = constfolding(op, e1, e2);
+  if (resf > 0)
     return;
-  else {
+  else if (resf == 0) {
     int o2 = (op != OP_UNM && op != OP_LEN) ? luaK_exp2RK(fs, e2) : 0;
     int o1 = luaK_exp2RK(fs, e1);
     if (o1 > o2) {
@@ -675,6 +676,8 @@ static void codearith (FuncState *fs, OpCode op, expdesc *e1, expdesc *e2) {
     e1->u.s.info = luaK_codeABC(fs, op, 0, o1, o2);
     e1->k = VRELOCABLE;
   }
+  else
+    luaX_syntaxerror(fs->ls, "Inf or NaN");
 }
 
 
diff --git a/apps/plugins/lua/lvm.c b/apps/plugins/lua/lvm.c
index ee3256ab94..acce53a858 100644
--- a/apps/plugins/lua/lvm.c
+++ b/apps/plugins/lua/lvm.c
@@ -480,13 +480,35 @@ void luaV_execute (lua_State *L, int nexeccalls) {
         continue;
       }
       case OP_DIV: {
-        arith_op(luai_numdiv, TM_DIV);
+        TValue *rb = RKB(i);
+        TValue *rc = RKC(i);
+        if (ttisnumber(rb) && ttisnumber(rc)) {
+          lua_Number nb = nvalue(rb), nc = nvalue(rc);
+          if (nc == 0)
+            luaG_typeerror(L, rc, "divide by zero");
+
+          setnvalue(ra, luai_numdiv(nb, nc));
+        }
+        else
+          Protect(Arith(L, ra, rb, rc, TM_DIV));
+
         continue;
       }
       case OP_MOD: {
-        arith_op(luai_nummod, TM_MOD);
+        TValue *rb = RKB(i);
+        TValue *rc = RKC(i);
+        if (ttisnumber(rb) && ttisnumber(rc)) {
+          lua_Number nb = nvalue(rb), nc = nvalue(rc);
+          if (nc == 0)
+            luaG_typeerror(L, rc, "perform 'n%0'");
+
+          setnvalue(ra, luai_nummod(nb, nc));
+        }
+        else
+          Protect(Arith(L, ra, rb, rc, TM_MOD));
+
         continue;
-      }
+    }
       case OP_POW: {
         arith_op(luai_numpow, TM_POW);
         continue;
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