IPv4: Add simple pseudorandom ephemeral port allocators for TCP and UDP.

Kernel/IPv4Socket.cpp

@@ -112,11 +112,15 @@ bool IPv4Socket::can_write(SocketRole) const
     return true;
 }
 
-void IPv4Socket::allocate_source_port_if_needed()
+int IPv4Socket::allocate_source_port_if_needed()
 {
     if (m_source_port)
-        return;
-    protocol_allocate_source_port();
+        return m_source_port;
+    int port = protocol_allocate_source_port();
+    if (port < 0)
+        return port;
+    m_source_port = (word)port;
+    return port;
 }
 
 ssize_t IPv4Socket::sendto(const void* data, size_t data_length, int flags, const sockaddr* addr, socklen_t addr_length)
@@ -142,7 +146,9 @@ ssize_t IPv4Socket::sendto(const void* data, size_t data_length, int flags, cons
         m_destination_port = ntohs(ia.sin_port);
     }
 
-    allocate_source_port_if_needed();
+    int rc = allocate_source_port_if_needed();
+    if (rc < 0)
+        return rc;
 
     kprintf("sendto: destination=%s:%u\n", m_destination_address.to_string().characters(), m_destination_port);
 

Kernel/IPv4Socket.h

@@ -45,12 +45,12 @@ public:
 protected:
     IPv4Socket(int type, int protocol);
 
-    void allocate_source_port_if_needed();
+    int allocate_source_port_if_needed();
 
     virtual int protocol_receive(const ByteBuffer&, void*, size_t, int, sockaddr*, socklen_t*) { return -ENOTIMPL; }
     virtual int protocol_send(const void*, int) { return -ENOTIMPL; }
     virtual KResult protocol_connect() { return KSuccess; }
-    virtual void protocol_allocate_source_port() { }
+    virtual int protocol_allocate_source_port() { return 0; }
     virtual bool protocol_is_disconnected() const { return false; }
 
 private:

Kernel/RandomDevice.cpp

@@ -16,12 +16,17 @@ RandomDevice::~RandomDevice()
 static unsigned long next = 1;
 
 #define MY_RAND_MAX 32767
-static int myrand()
+int RandomDevice::random_value()
 {
     next = next * 1103515245 + 12345;
     return((unsigned)(next/((MY_RAND_MAX + 1) * 2)) % (MY_RAND_MAX + 1));
 }
 
+float RandomDevice::random_percentage()
+{
+    return (float)random_value() / (float)MY_RAND_MAX;
+}
+
 #if 0
 static void mysrand(unsigned seed)
 {
@@ -39,7 +44,7 @@ ssize_t RandomDevice::read(Process&, byte* buffer, ssize_t size)
     const int range = 'z' - 'a';
     ssize_t nread = min(size, GoodBufferSize);
     for (ssize_t i = 0; i < nread; ++i) {
-        dword r = myrand() % range;
+        dword r = random_value() % range;
         buffer[i] = (byte)('a' + r);
     }
     return nread;

Kernel/RandomDevice.h

@@ -8,6 +8,9 @@ public:
     RandomDevice();
     virtual ~RandomDevice() override;
 
+    static int random_value();
+    static float random_percentage();
+
 private:
     // ^CharacterDevice
     virtual ssize_t read(Process&, byte*, ssize_t) override;

Kernel/TCPSocket.cpp

@@ -2,6 +2,7 @@
 #include <Kernel/TCP.h>
 #include <Kernel/NetworkAdapter.h>
 #include <Kernel/Process.h>
+#include <Kernel/RandomDevice.h>
 
 Lockable<HashMap<word, TCPSocket*>>& TCPSocket::sockets_by_port()
 {
@@ -173,19 +174,28 @@ KResult TCPSocket::protocol_connect()
     return KSuccess;
 }
 
-void TCPSocket::protocol_allocate_source_port()
+int TCPSocket::protocol_allocate_source_port()
 {
-    // This is not a very efficient allocation algorithm.
-    // FIXME: Replace it with a bitmap or some other fast-paced looker-upper.
+    static const word first_ephemeral_port = 32768;
+    static const word last_ephemeral_port = 60999;
+    static const word ephemeral_port_range_size = last_ephemeral_port - first_ephemeral_port;
+    word first_scan_port = first_ephemeral_port + (word)(RandomDevice::random_percentage() * ephemeral_port_range_size);
+
     LOCKER(sockets_by_port().lock());
-    for (word port = 2000; port < 60000; ++port) {
+    for (word port = first_scan_port;;) {
         auto it = sockets_by_port().resource().find(port);
         if (it == sockets_by_port().resource().end()) {
             set_source_port(port);
             sockets_by_port().resource().set(port, this);
-            return;
+            return port;
         }
+        ++port;
+        if (port > last_ephemeral_port)
+            port = first_ephemeral_port;
+        if (port == first_scan_port)
+            break;
     }
+    return -EADDRINUSE;
 }
 
 bool TCPSocket::protocol_is_disconnected() const

Kernel/TCPSocket.h

@@ -35,7 +35,7 @@ private:
     virtual int protocol_receive(const ByteBuffer&, void* buffer, size_t buffer_size, int flags, sockaddr* addr, socklen_t* addr_length) override;
     virtual int protocol_send(const void*, int) override;
     virtual KResult protocol_connect() override;
-    virtual void protocol_allocate_source_port() override;
+    virtual int protocol_allocate_source_port() override;
     virtual bool protocol_is_disconnected() const override;
 
     dword m_sequence_number { 0 };

Kernel/UDPSocket.cpp

@@ -2,6 +2,7 @@
 #include <Kernel/UDP.h>
 #include <Kernel/NetworkAdapter.h>
 #include <Kernel/Process.h>
+#include <Kernel/RandomDevice.h>
 
 Lockable<HashMap<word, UDPSocket*>>& UDPSocket::sockets_by_port()
 {
@@ -83,17 +84,26 @@ KResult UDPSocket::protocol_connect()
     return KSuccess;
 }
 
-void UDPSocket::protocol_allocate_source_port()
+int UDPSocket::protocol_allocate_source_port()
 {
-    // This is not a very efficient allocation algorithm.
-    // FIXME: Replace it with a bitmap or some other fast-paced looker-upper.
+    static const word first_ephemeral_port = 32768;
+    static const word last_ephemeral_port = 60999;
+    static const word ephemeral_port_range_size = last_ephemeral_port - first_ephemeral_port;
+    word first_scan_port = first_ephemeral_port + (word)(RandomDevice::random_percentage() * ephemeral_port_range_size);
+
     LOCKER(sockets_by_port().lock());
-    for (word port = 2000; port < 60000; ++port) {
+    for (word port = first_scan_port;;) {
         auto it = sockets_by_port().resource().find(port);
         if (it == sockets_by_port().resource().end()) {
             set_source_port(port);
             sockets_by_port().resource().set(port, this);
-            return;
+            return port;
         }
+        ++port;
+        if (port > last_ephemeral_port)
+            port = first_ephemeral_port;
+        if (port == first_scan_port)
+            break;
     }
+    return -EADDRINUSE;
 }

Kernel/UDPSocket.h

@@ -18,7 +18,7 @@ private:
     virtual int protocol_receive(const ByteBuffer&, void* buffer, size_t buffer_size, int flags, sockaddr* addr, socklen_t* addr_length) override;
     virtual int protocol_send(const void*, int) override;
     virtual KResult protocol_connect() override;
-    virtual void protocol_allocate_source_port() override;
+    virtual int protocol_allocate_source_port() override;
 };
 
 class UDPSocketHandle : public SocketHandle {