From a65e7db533adb567b05859a574042b76e5912a6c Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 14 Nov 2020 11:23:39 +0100
Subject: [PATCH] LibC: Fix OOB access in strerror() with invalid input

Calling strerror() with a negative number should not access below the
error string array.

Found by running GCC in UE. :^)
---
 Libraries/LibC/string.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Libraries/LibC/string.cpp b/Libraries/LibC/string.cpp
index 5bd872d4f8..56eadb2c26 100644
--- a/Libraries/LibC/string.cpp
+++ b/Libraries/LibC/string.cpp
@@ -372,7 +372,7 @@ int sys_nerr = EMAXERRNO;
 
 char* strerror(int errnum)
 {
-    if (errnum >= EMAXERRNO) {
+    if (errnum < 0 || errnum >= EMAXERRNO) {
         printf("strerror() missing string for errnum=%d\n", errnum);
         return const_cast<char*>("Unknown error");
     }