From efcf24be0c22cba57b298161bf4ab0561fd3c08e Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Fri, 22 May 2020 15:39:29 -0300
Subject: [PATCH] 'luaL_execresult' does not assume -1 status as error

ISO C is silent about the return of 'system'. Windows sets 'errno' in
case of errors. Linux has several different error cases, with different
return values. ISO C allows 'system' to set 'errno' even if there are no
errors. Here we assume that a status==0 is success (which is the case
on several platforms), otherwise it is an error. If there is an error
number, gives the error based on it. (The worst a spurious 'errno'
can do is to generate a bad error message.) Otherwise uses the normal
results.
---
 lauxlib.c | 2 +-
 liolib.c  | 1 +
 loslib.c  | 6 ++++--
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/lauxlib.c b/lauxlib.c
index a5e9e4b5..f2ba704f 100644
--- a/lauxlib.c
+++ b/lauxlib.c
@@ -284,7 +284,7 @@ LUALIB_API int luaL_fileresult (lua_State *L, int stat, const char *fname) {
 
 LUALIB_API int luaL_execresult (lua_State *L, int stat) {
   const char *what = "exit";  /* type of termination */
-  if (stat == -1)  /* error? */
+  if (stat != 0 && errno != 0)  /* error with an 'errno'? */
     return luaL_fileresult(L, 0, NULL);
   else {
     l_inspectstat(stat, what);  /* interpret result */
diff --git a/liolib.c b/liolib.c
index 08d18397..7ac34443 100644
--- a/liolib.c
+++ b/liolib.c
@@ -270,6 +270,7 @@ static int io_open (lua_State *L) {
 */
 static int io_pclose (lua_State *L) {
   LStream *p = tolstream(L);
+  errno = 0;
   return luaL_execresult(L, l_pclose(L, p->f));
 }
 
diff --git a/loslib.c b/loslib.c
index 5e0fafb4..e65e188b 100644
--- a/loslib.c
+++ b/loslib.c
@@ -10,6 +10,7 @@
 #include "lprefix.h"
 
 
+#include <errno.h>
 #include <locale.h>
 #include <stdlib.h>
 #include <string.h>
@@ -138,10 +139,11 @@
 
 
 
-
 static int os_execute (lua_State *L) {
   const char *cmd = luaL_optstring(L, 1, NULL);
-  int stat = system(cmd);
+  int stat;
+  errno = 0;
+  stat = system(cmd);
   if (cmd != NULL)
     return luaL_execresult(L, stat);
   else {