From 2bf11b83480975da0e43dcb5726dbd3b9a0c480c Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 25 Jan 2020 14:14:11 +0100
Subject: [PATCH] Kernel: Allow empty strings in
 validate_and_copy_string_from_user()

Sergey pointed out that we should just allow empty strings everywhere.
---
 Kernel/Process.cpp | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index 5ccf2074ec..02f470fb7f 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -1163,13 +1163,10 @@ int Process::sys$execve(const Syscall::SC_execve_params* user_params)
         strings.resize(list.length);
         copy_from_user(strings.data(), list.strings, list.length * sizeof(Syscall::StringArgument));
         for (size_t i = 0; i < list.length; ++i) {
-            if (strings[i].length == 0) {
-                output.append(String::empty());
-                continue;
-            }
-            if (!validate_read(strings[i].characters, strings[i].length))
+            auto string = validate_and_copy_string_from_user(strings[i]);
+            if (string.is_null())
                 return false;
-            output.append(copy_string_from_user(strings[i].characters, strings[i].length));
+            output.append(move(string));
         }
         return true;
     };
@@ -1801,10 +1798,10 @@ bool Process::validate(const Syscall::ImmutableBufferArgument<DataType, SizeType
 
 String Process::validate_and_copy_string_from_user(const char* user_characters, size_t user_length) const
 {
-    if (!user_characters)
-        return {};
     if (user_length == 0)
         return String::empty();
+    if (!user_characters)
+        return {};
     if (!validate_read(user_characters, user_length))
         return {};
     SmapDisabler disabler;