From e1db8094b61aae6493cb10426b09d5f4c7177e8f Mon Sep 17 00:00:00 2001
From: Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
Date: Fri, 12 Feb 2021 18:23:28 +0100
Subject: [PATCH] Kernel: Avoid casting arbitrary user-controlled int to enum

This caused a load-invalid-value warning by KUBSan.

Found by fuzz-syscalls. Can be reproduced by running this in the Shell:

    $ syscall waitid [ 1234 ]
---
 Kernel/Syscalls/waitid.cpp | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/Kernel/Syscalls/waitid.cpp b/Kernel/Syscalls/waitid.cpp
index eeb471f947..d9dc09f509 100644
--- a/Kernel/Syscalls/waitid.cpp
+++ b/Kernel/Syscalls/waitid.cpp
@@ -31,15 +31,6 @@ namespace Kernel {
 
 KResultOr<siginfo_t> Process::do_waitid(idtype_t idtype, int id, int options)
 {
-    switch (idtype) {
-    case P_ALL:
-    case P_PID:
-    case P_PGID:
-        break;
-    default:
-        return EINVAL;
-    }
-
     KResultOr<siginfo_t> result = KResult(KSuccess);
     if (Thread::current()->block<Thread::WaitBlocker>({}, options, idtype, id, result).was_interrupted())
         return EINTR;
@@ -55,6 +46,15 @@ pid_t Process::sys$waitid(Userspace<const Syscall::SC_waitid_params*> user_param
     if (!copy_from_user(&params, user_params))
         return -EFAULT;
 
+    switch (params.idtype) {
+    case P_ALL:
+    case P_PID:
+    case P_PGID:
+        break;
+    default:
+        return EINVAL;
+    }
+
     dbgln_if(PROCESS_DEBUG, "sys$waitid({}, {}, {}, {})", params.idtype, params.id, params.infop, params.options);
 
     auto siginfo_or_error = do_waitid(static_cast<idtype_t>(params.idtype), params.id, params.options);