Kernel: Add the SO_BINDTODEVICE socket option

This patch adds a way for a socket to ask to be routed through a
specific interface.
Currently, this option only applies to sending, however, it should also
apply to receiving...somehow :^)

Kernel/Net/IPv4Socket.cpp

@@ -210,7 +210,7 @@ ssize_t IPv4Socket::sendto(FileDescription&, const void* data, size_t data_lengt
         m_peer_port = ntohs(ia.sin_port);
     }
 
-    auto routing_decision = route_to(m_peer_address, m_local_address);
+    auto routing_decision = route_to(m_peer_address, m_local_address, bound_interface());
     if (routing_decision.is_zero())
         return -EHOSTUNREACH;
 

Kernel/Net/Routing.cpp

@@ -46,10 +46,22 @@ bool RoutingDecision::is_zero() const
     return adapter.is_null() || next_hop.is_zero();
 }
 
-RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source)
+RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source, const RefPtr<NetworkAdapter> through)
 {
+    auto matches = [&](auto& adapter) {
+        if (!through)
+            return true;
+
+        return through == adapter;
+    };
+    auto if_matches = [&](auto& adapter, const auto& mac) -> RoutingDecision {
+        if (!matches(adapter))
+            return { nullptr, {} };
+        return { adapter, mac };
+    };
+
     if (target[0] == 127)
-        return { LoopbackAdapter::the(), LoopbackAdapter::the().mac_address() };
+        return if_matches(LoopbackAdapter::the(), LoopbackAdapter::the().mac_address());
 
     auto target_addr = target.to_u32();
     auto source_addr = source.to_u32();
@@ -57,17 +69,17 @@ RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source)
     RefPtr<NetworkAdapter> local_adapter = nullptr;
     RefPtr<NetworkAdapter> gateway_adapter = nullptr;
 
-    NetworkAdapter::for_each([source_addr, &target_addr, &local_adapter, &gateway_adapter](auto& adapter) {
+    NetworkAdapter::for_each([source_addr, &target_addr, &local_adapter, &gateway_adapter, &matches](auto& adapter) {
         auto adapter_addr = adapter.ipv4_address().to_u32();
         auto adapter_mask = adapter.ipv4_netmask().to_u32();
 
         if (source_addr != 0 && source_addr != adapter_addr)
             return;
 
-        if ((target_addr & adapter_mask) == (adapter_addr & adapter_mask))
+        if ((target_addr & adapter_mask) == (adapter_addr & adapter_mask) && matches(adapter))
             local_adapter = adapter;
 
-        if (adapter.ipv4_gateway().to_u32() != 0)
+        if (adapter.ipv4_gateway().to_u32() != 0 && matches(adapter))
             gateway_adapter = adapter;
     });
 

Kernel/Net/Routing.h

@@ -37,7 +37,7 @@ struct RoutingDecision {
     bool is_zero() const;
 };
 
-RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source);
+RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source, const RefPtr<NetworkAdapter> through = nullptr);
 
 Lockable<HashMap<IPv4Address, MACAddress>>& arp_table();
 

Kernel/Net/Socket.cpp

@@ -25,6 +25,7 @@
  */
 
 #include <AK/StringBuilder.h>
+#include <AK/StringView.h>
 #include <Kernel/FileSystem/FileDescription.h>
 #include <Kernel/Net/IPv4Socket.h>
 #include <Kernel/Net/LocalSocket.h>
@@ -114,6 +115,16 @@ KResult Socket::setsockopt(int level, int option, const void* value, socklen_t v
             return KResult(-EINVAL);
         m_receive_timeout = *(const timeval*)value;
         return KSuccess;
+    case SO_BINDTODEVICE: {
+        if (value_size != IFNAMSIZ)
+            return KResult(-EINVAL);
+        StringView ifname { (const char*)value };
+        auto device = NetworkAdapter::lookup_by_name(ifname);
+        if (!device)
+            return KResult(-ENODEV);
+        m_bound_interface = device;
+        return KSuccess;
+    }
     default:
         dbg() << "setsockopt(" << option << ") at SOL_SOCKET not implemented.";
         return KResult(-ENOPROTOOPT);
@@ -143,6 +154,19 @@ KResult Socket::getsockopt(FileDescription&, int level, int option, void* value,
         *(int*)value = 0;
         *value_size = sizeof(int);
         return KSuccess;
+    case SO_BINDTODEVICE:
+        if (*value_size < IFNAMSIZ)
+            return KResult(-EINVAL);
+        if (m_bound_interface) {
+            const auto& name = m_bound_interface->name();
+            auto length = name.length() + 1;
+            memcpy(value, name.characters(), length);
+            *value_size = length;
+            return KSuccess;
+        } else {
+            *value_size = 0;
+            return KResult(-EFAULT);
+        }
     default:
         dbg() << "getsockopt(" << option << ") at SOL_SOCKET not implemented.";
         return KResult(-ENOPROTOOPT);

Kernel/Net/Socket.h

@@ -33,6 +33,7 @@
 #include <Kernel/FileSystem/File.h>
 #include <Kernel/KResult.h>
 #include <Kernel/Lock.h>
+#include <Kernel/Net/NetworkAdapter.h>
 #include <Kernel/UnixTypes.h>
 
 namespace Kernel {
@@ -57,9 +58,9 @@ public:
     bool is_shut_down_for_reading() const { return m_shut_down_for_reading; }
 
     enum class SetupState {
-        Unstarted,  // we haven't tried to set the socket up yet
+        Unstarted, // we haven't tried to set the socket up yet
         InProgress, // we're in the process of setting things up - for TCP maybe we've sent a SYN packet
-        Completed,  // the setup process is complete, but not necessarily successful
+        Completed, // the setup process is complete, but not necessarily successful
     };
 
     enum class Role : u8 {
@@ -118,6 +119,7 @@ public:
     pid_t acceptor_pid() const { return m_acceptor.pid; }
     uid_t acceptor_uid() const { return m_acceptor.uid; }
     gid_t acceptor_gid() const { return m_acceptor.gid; }
+    const RefPtr<NetworkAdapter> bound_interface() const { return m_bound_interface; }
 
     Lock& lock() { return m_lock; }
 
@@ -165,13 +167,15 @@ private:
     bool m_shut_down_for_reading { false };
     bool m_shut_down_for_writing { false };
 
+    RefPtr<NetworkAdapter> m_bound_interface { nullptr };
+
     timeval m_receive_timeout { 0, 0 };
     timeval m_send_timeout { 0, 0 };
 
     NonnullRefPtrVector<Socket> m_pending;
 };
 
-template<typename SocketType>
+template <typename SocketType>
 class SocketHandle {
 public:
     SocketHandle() {}

Kernel/Net/TCPSocket.cpp

@@ -212,7 +212,7 @@ void TCPSocket::send_tcp_packet(u16 flags, const void* payload, size_t payload_s
         return;
     }
 
-    auto routing_decision = route_to(peer_address(), local_address());
+    auto routing_decision = route_to(peer_address(), local_address(), bound_interface());
     ASSERT(!routing_decision.is_zero());
 
     routing_decision.adapter->send_ipv4(
@@ -225,7 +225,7 @@ void TCPSocket::send_tcp_packet(u16 flags, const void* payload, size_t payload_s
 
 void TCPSocket::send_outgoing_packets()
 {
-    auto routing_decision = route_to(peer_address(), local_address());
+    auto routing_decision = route_to(peer_address(), local_address(), bound_interface());
     ASSERT(!routing_decision.is_zero());
 
     auto now = kgettimeofday();

Kernel/Net/UDPSocket.cpp

@@ -92,7 +92,7 @@ int UDPSocket::protocol_receive(const KBuffer& packet_buffer, void* buffer, size
 
 int UDPSocket::protocol_send(const void* data, size_t data_length)
 {
-    auto routing_decision = route_to(peer_address(), local_address());
+    auto routing_decision = route_to(peer_address(), local_address(), bound_interface());
     if (routing_decision.is_zero())
         return -EHOSTUNREACH;
     auto buffer = ByteBuffer::create_zeroed(sizeof(UDPPacket) + data_length);

Kernel/UnixTypes.h

@@ -401,6 +401,7 @@ struct pollfd {
 #define SO_ERROR 4
 #define SO_PEERCRED 5
 #define SO_REUSEADDR 6
+#define SO_BINDTODEVICE 7
 
 #define IPPROTO_IP 0
 #define IPPROTO_ICMP 1