Kernel: Stop modifying peer address/port in sendto on a TCP socket

POSIX (rightfully so) specifies that the sendto address argument is
ignored in connection-oriented protocols.

The TCPSocket also assumed the peer address may not change post-connect
and would trigger a UAF in sockets_by_tuple() when it did.

Kernel/Net/IPv4Socket.cpp

@@ -204,9 +204,11 @@ ErrorOr<size_t> IPv4Socket::sendto(OpenFileDescription&, UserOrKernelBuffer cons
             return set_so_error(EAFNOSUPPORT);
         }
 
+        if (type() != SOCK_STREAM) {
             m_peer_address = IPv4Address((u8 const*)&ia.sin_addr.s_addr);
             m_peer_port = ntohs(ia.sin_port);
         }
+    }
 
     if (!is_connected() && m_peer_address.is_zero())
         return set_so_error(EPIPE);

Tests/Kernel/CMakeLists.txt

@@ -56,6 +56,7 @@ set(LIBTEST_BASED_SOURCES
     TestSigAltStack.cpp
     TestSigHandler.cpp
     TestSigWait.cpp
+    TestTCPSocket.cpp
 )
 
 if (NOT CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64")

Tests/Kernel/TestTCPSocket.cpp

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2023, Idan Horowitz <idan.horowitz@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+#include <netinet/in.h>
+#include <pthread.h>
+#include <sys/socket.h>
+
+static constexpr u16 port = 1337;
+
+static void* server_handler(void*)
+{
+    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
+    EXPECT(server_fd >= 0);
+
+    sockaddr_in sin {};
+    sin.sin_family = AF_INET;
+    sin.sin_port = htons(port);
+    sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    int rc = bind(server_fd, (sockaddr*)(&sin), sizeof(sin));
+    EXPECT_EQ(rc, 0);
+
+    rc = listen(server_fd, 1);
+    EXPECT_EQ(rc, 0);
+
+    int client_fd = accept(server_fd, nullptr, nullptr);
+    EXPECT(client_fd >= 0);
+
+    u8 data;
+    int nread = recv(client_fd, &data, sizeof(data), 0);
+    EXPECT_EQ(nread, 1);
+    EXPECT_EQ(data, 'A');
+
+    rc = close(client_fd);
+    EXPECT_EQ(rc, 0);
+
+    rc = close(server_fd);
+    EXPECT_EQ(rc, 0);
+
+    pthread_exit(nullptr);
+    VERIFY_NOT_REACHED();
+}
+
+static pthread_t start_tcp_server()
+{
+    pthread_t thread;
+    int rc = pthread_create(&thread, nullptr, server_handler, nullptr);
+    EXPECT_EQ(rc, 0);
+    return thread;
+}
+
+TEST_CASE(tcp_sendto)
+{
+    pthread_t server = start_tcp_server();
+
+    int client_fd = socket(AF_INET, SOCK_STREAM, 0);
+    EXPECT(client_fd >= 0);
+
+    sockaddr_in sin {};
+    sin.sin_family = AF_INET;
+    sin.sin_port = htons(port);
+    sin.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    int rc = connect(client_fd, (sockaddr*)(&sin), sizeof(sin));
+    EXPECT_EQ(rc, 0);
+
+    u8 data = 'A';
+    sockaddr_in dst {};
+    dst.sin_family = AF_INET;
+    dst.sin_port = htons(port + 1); // Different port, should be ignored
+    dst.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    int nwritten = sendto(client_fd, &data, sizeof(data), 0, (sockaddr*)(&dst), sizeof(dst));
+    EXPECT_EQ(nwritten, 1);
+
+    rc = close(client_fd);
+    EXPECT_EQ(rc, 0);
+
+    rc = pthread_join(server, nullptr);
+    EXPECT_EQ(rc, 0);
+}