From 532db9f76881b574924b7fb26772cc911e343a5a Mon Sep 17 00:00:00 2001
From: Gunnar Beutner <gbeutner@serenityos.org>
Date: Wed, 12 May 2021 12:14:03 +0200
Subject: [PATCH] Kernel: Treat 0.0.0.0 as a loopback address

This matches what other operating systems like Linux do:

$ ip route get 0.0.0.0
local 0.0.0.0 dev lo src 127.0.0.1 uid 1000
    cache <local>

$ ssh 0.0.0.0
gunnar@0.0.0.0's password:

$ ss -na | grep :22 | grep ESTAB
tcp   ESTAB      0      0   127.0.0.1:43118   127.0.0.1:22
tcp   ESTAB      0      0   127.0.0.1:22      127.0.0.1:43118
---
 Kernel/Net/IPv4Socket.cpp     | 2 ++
 Kernel/Net/NetworkAdapter.cpp | 2 ++
 Kernel/Net/Routing.cpp        | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/Kernel/Net/IPv4Socket.cpp b/Kernel/Net/IPv4Socket.cpp
index 62fd5cec4d..ad039cd4e7 100644
--- a/Kernel/Net/IPv4Socket.cpp
+++ b/Kernel/Net/IPv4Socket.cpp
@@ -139,6 +139,8 @@ KResult IPv4Socket::connect(FileDescription& description, Userspace<const sockad
         return EFAULT;
 
     m_peer_address = IPv4Address((const u8*)&safe_address.sin_addr.s_addr);
+    if (m_peer_address == IPv4Address { 0, 0, 0, 0 })
+        m_peer_address = IPv4Address { 127, 0, 0, 1 };
     m_peer_port = ntohs(safe_address.sin_port);
 
     return protocol_connect(description, should_block);
diff --git a/Kernel/Net/NetworkAdapter.cpp b/Kernel/Net/NetworkAdapter.cpp
index 7a72bcc868..d310912a55 100644
--- a/Kernel/Net/NetworkAdapter.cpp
+++ b/Kernel/Net/NetworkAdapter.cpp
@@ -40,6 +40,8 @@ RefPtr<NetworkAdapter> NetworkAdapter::from_ipv4_address(const IPv4Address& addr
         if (adapter->ipv4_address() == address || adapter->ipv4_broadcast() == address)
             return adapter;
     }
+    if (address[0] == 0 && address[1] == 0 && address[2] == 0 && address[3] == 0)
+        return LoopbackAdapter::the();
     if (address[0] == 127)
         return LoopbackAdapter::the();
     return nullptr;
diff --git a/Kernel/Net/Routing.cpp b/Kernel/Net/Routing.cpp
index e207cd35f4..3c6a6d0aac 100644
--- a/Kernel/Net/Routing.cpp
+++ b/Kernel/Net/Routing.cpp
@@ -141,6 +141,8 @@ RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source, c
         return { adapter, mac };
     };
 
+    if (target[0] == 0 && target[1] == 0 && target[2] == 0 && target[3] == 0)
+        return if_matches(LoopbackAdapter::the(), LoopbackAdapter::the().mac_address());
     if (target[0] == 127)
         return if_matches(LoopbackAdapter::the(), LoopbackAdapter::the().mac_address());