From 32aa623effb520111d4598619e425f336e0e78f0 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Fri, 17 Dec 2021 14:45:09 +0100
Subject: [PATCH] Kernel: Fix 4-byte uninitialized memory leak in
 sys$sigaltstack()

It was possible to extract 4 bytes of uninitialized kernel stack memory
on x86_64 by looking in the padding of stack_t.
---
 Kernel/Syscalls/sigaction.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Kernel/Syscalls/sigaction.cpp b/Kernel/Syscalls/sigaction.cpp
index ed25c544e3..0b4ca0db42 100644
--- a/Kernel/Syscalls/sigaction.cpp
+++ b/Kernel/Syscalls/sigaction.cpp
@@ -262,7 +262,7 @@ ErrorOr<FlatPtr> Process::sys$sigaltstack(Userspace<const stack_t*> user_ss, Use
     REQUIRE_PROMISE(sigaction);
 
     if (user_old_ss) {
-        stack_t old_ss_value;
+        stack_t old_ss_value {};
         old_ss_value.ss_sp = (void*)Thread::current()->m_alternative_signal_stack;
         old_ss_value.ss_size = Thread::current()->m_alternative_signal_stack_size;
         old_ss_value.ss_flags = 0;